All language subtitles for English (auto-generated)_en_0_JavaScript Tutorial Full Course - Beginner to Pro(1080P_60FPS)

welcome to the complete JavaScript

course in this course we're going to

learn how to build complex websites

using JavaScript from a beginner to a

professional level and by the end of

this course we're going to build

amazon.com so this is an interactive

multi-page website where we can add

products to our cart create an order and

even track our

order along the way we're also going to

build some smaller projects like a rock

paper scissors game a to-do list and a

calculator now you don't need any

previous coding or technical experience

to follow along this course will cover

everything that you need to learn

JavaScript we're going to start from the

very basics of JavaScript and we're

going to build our way up step by step

we're going to learn the major features

of JavaScript and also how to use

JavaScript together with other

Technologies like HTML and

CSS we're also going to learn more

advanced features like objectoriented

programming backend callbacks promises

and async await and we'll use these

features together to build a complex

project which is the Amazon

Project this will let you practice what

you learn and deepen your

understanding you can find the different

lessons of this course course below the

video

here and

here if you need to you can adjust the

speed of the video

here and after each lesson I'm going to

give you a bunch of exercises that you

can do on your own to practice the

skills that we learned in total this

course will have over

250 exercises so with that said let's

get started

before we begin if something in this

course is not working properly make sure

to check the first comment below the

video for a list of

solutions I'm going to be doing this

course on Windows but the steps are the

same if you're using a Mac we're going

to start from the very basics of

JavaScript and build our way up step by

step first of all what is Javascript

JavaScript is a technology that we use

to create websites a website is like

youtube.com or

amazon.com it's how we access YouTube

and Amazon on our computer if we were

using a phone we usually use an app but

on our computer we use a

website so there's actually three

technologies that we use to create

websites HTML CSS and JavaScript each of

these Technologies has a specific

purpose when creating a website HTML

creates the content of a website it

creates all the buttons the text and the

images CSS changes the appearance of the

website by adding CSS we can make our

website look nice and finally JavaScript

makes our website

interactive so if we only have HTML and

CSS and we click one of these buttons

our website doesn't do anything but once

we add JavaScript we can make our

website do something when we click a

button such as add a product to our cart

or create an

order so this course is focused on

JavaScript if you want to learn HTML and

CSS in more detail I have a full whole

course just like this one that you can

find in the video

description let's get started with

JavaScript the first thing we need to do

is to install a piece of software called

a web browser a web browser lets us view

websites that we create in this course

the most popular web browser for web

development is Google Chrome so I

recommend using that if you don't have

Google Chrome you can open the default

web browser on your computer for windows

it's Microsoft Edge and for Mac it's

Safari type in google.com at the top and

press enter search for Google

Chrome click the result and follow the

instructions to download and install

once we've installed Chrome we're ready

to

begin we're going to start by learning

what exactly is Javascript and how does

it work the easiest way to understand

JavaScript is we're basically giving

instructions to a computer and then the

computer follows our

instructions I find the best way to

learn this is to jump in and give it a

try so first let's open Google

Chrome next we're going to click at the

top

here and type

super

simple

dodev slj

s- Basics and press

enter and now we'll learn how to give

our computer some instructions to follow

to do that we're going to go to a blank

area of the web page we're going to

rightclick click

inspect and then click the console

tab now if your console doesn't show up

at the bottom like this you can click

these three dots here here and then

select this

icon okay so inside the console we can

give some instructions for our computer

let's learn our first instruction we're

going to type here and we're going to

type

alert Open Bracket single quote hello

single quote close bracket and

semicolon make sure to type this out

exactly as I have it here in JavaScript

if you don't type things out correctly

it won't work so this is an instruction

to create a popup with the text hello

inside to get the computer to follow our

instruction we can just press

enter and as you can see the computer

does exactly what we tell it to do it

creates a popup with a text hello

inside now let's press

okay and let's give another instruction

to the computer so we're going to type

here again and we're going to type alert

again Open Bracket single quote but this

time we're going to type a different

message in the

popup good job and single quote close

bracket and

semicolon so this is an instruction to

create a popup again but this time with

a text good job in inside the popup if

we press

enter the computer does exactly what we

tell it to do and it creates a popup

with the text good job inside and that's

basically the main idea behind

JavaScript we're giving instructions to

a computer and then the computer follows

our

instructions so note that we can open

and use this console on any website

we're just using superimple dodev as an

example

let's press

okay and we're going to learn some

terminology or

naming the instructions we give to our

computer these instructions are called

code when we press enter and the

computer follows our instructions this

is called running the code now there are

many different languages we can use to

write code called programming languages

it's similar to how we have many human

Lang languages that we can use to

communicate some examples of programming

languages are JavaScript Python and Java

so here we're writing our code using the

JavaScript programming language so we

call this JavaScript

code now that we understand the basic

terminology let's look at some more

examples of what we can do with

JavaScript code another thing we can do

is

math let's go back to the console and

type here and we're going to type 2 + 2

so this is an instruction or code that

tells the computer to do some math to

calculate 2 + 2 when we press

enter the computer follows our

instruction or runs this code calculates

2+ 2 and gives us the result which is

four let's do another example we're

going to type 10 minus 3 and press enter

to run this code again the computer does

this math calculates the result and

gives us seven so as you can see

JavaScript can do many different things

like create popups and do math let's

look at one more example of what

JavaScript can do we're going to go to

the bottom and type out this code

document.body do inner Capital

HTML equals single quilt hello single

quilt and

semicolon make sure to write this out

exactly as I have it here with the dots

and the capital letters because

JavaScript is case

sensitive let's press enter to run this

code what this code does is that it

removes everything on the page and

replaces it with the text hello in this

example we use JavaScript to modify the

web page modifying the web page is one

of the most important features of

JavaScript and we're going to be using

this feature throughout this course and

that's the basics of JavaScript we're

giving instructions to a computer these

instructions are called code and then

the computer follows our instru

instuctions this is called running the

code and also don't worry about

memorizing all this code you can find a

copy of all the code that we write in

this course in the video

description now that we understand the

basics of JavaScript let's learn more

about the JavaScript language

itself if we take a look at this code

alert and hello you might be wondering

ing what the brackets and the quote mean

all of these characters have a special

meaning in the language this is

something called

syntax syntax are the rules that we have

to follow when using a programming

language like JavaScript this is sort of

like in English we also have rules that

we follow called grammar the difference

is that in English we don't have to

follow the rules of grammar perfectly

people can still understand us but in

programming we have to follow the rules

of syntax exactly otherwise the computer

won't understand our code for example if

we scroll down and we type this code

alert Open Bracket quote hello quote

close bracket and semicolon but this

time we remove the first bracket and

press

enter it will give us a syntax error

we're not following the rules of syntax

so the computer doesn't understand this

code now JavaScript has a lot of syntax

rules and we can't learn them all at

once right now instead we're going to

learn the syntax rules one by one as we

go through the course for now we'll just

learn enough syntax to do the exercises

at the end of this lesson what we need

to know is that if we scroll up

this part of the code tells a computer

to create a popup the text between these

quotes is the text inside the popup if

we change this text we can change the

text inside the popup same thing for

this code down

here if we change the text between the

quotes it will change the text that

appears on the page and that's all we

need to know about JavaScript Syntax for

now we'll learn exact ly what the other

characters like the brackets quotes and

semicolon mean later on in this course

so in this lesson we learned that

JavaScript is basically giving

instructions to a computer we wrote our

first few lines of JavaScript code we

learned how to run our code using the

console in our web browser and we

learned about syntax which are the rules

that we have to follow when writing our

code

thanks for watching this course so far

if you want to support this channel you

can check out the premium version of my

courses just like this one where you can

get a certificate of completion and a

Better Learning platform if you're

interested in extra videos from me more

in-depth videos and behind the scenes

content you can check out these links

here you can also support the channel by

liking the video subscribing and sharing

this video with others

thanks again and let's continue with the

course here are some exercises you can

try on your own to practice what we

learned in this

lesson you can find the solutions to

these exercises in the video

description now that we understand the

basics of JavaScript we're going to

learn about each feature of the language

language in this lesson we're going to

focus on numbers and math first we can

close the console for

now so I've actually prepared a project

that we can use for this lesson to open

this project we're going to go to our

browser click up here and type

super simple

dodev SL

projects SL Amazon

and press

enter so this is actually the final

project we're going to create in this

course this is an e-commerce website

similar to Amazon where we can add

products to our cart and then view our

cart by clicking the top

right and on this page we can see the

products in our cart modify our cart and

create an

order for this lesson we're going to

focus on this right section which

calculates the cost of our cart

including the cost of the products

shipping and

taxes this section is a great way to

learn numbers and math in

JavaScript first let's open the console

again so we can write JavaScript code

we're going to find a blank area of the

web page rightclick click

inspect and then click the

console so we already saw some examples

of math in the previous lesson for

example we wrote the code 2 + 2 if we

press

enter the computer adds these two

numbers and results in

four we also did 10 minus 3 if we press

enter the computer subtracts these two

numbers and gives us

seven in addition to adding and

subtracting we can also multiply and

divide to multiply we're going to type

10 star 3 and press

enter so star is the character for

multiplying to divide we're going to

type

10

slash2 and press enter

so forward slash is the character for

dividing now let's learn the syntax

rules for numbers and math the Syntax

for math is pretty straightforward in

JavaScript we just write it out like

normal math we can also do math with

more than two numbers for example we can

add two plus 2 and then plus another two

if if we press enter the computer will

add these three numbers together and

result in six and finally JavaScript can

handle decimal numbers like

2.2 plus

2.2 if we press enter it will calculate

these decimal numbers and result in

4.4 now let's do some practical examples

we're going to calculate the number

numers here in our final project but

first let's set up our cart so we have

the same products in our cart so make

sure in your cart you have two socks

with free shipping and you have one

basketball with

$4.99 of shipping and nothing else in

your cart if you need to you can modify

your cart by clicking update or delete

or or by going to the homepage by

clicking in the top left and adding any

products that you're

missing once you have the same products

as me in your cart and you have the same

numbers on the right we're ready to

begin let's start by calculating this

number up here this is the cost of the

products before shipping and taxes to

calculate this number using JavaScript

we're just going to add the cost of the

products so in our console we're going

to add the cost of the socks which is

$10 and

90 we have two of them so we're going to

multiply this by

two and then we're going to add the cost

of the basketball so plus

$20.95 if we press

enter the computer will do this math

calculation

and give us this number and if we scroll

to the top of our

project you'll see that the number that

we got matches what we have on the page

so that's how we use JavaScript to

calculate this number here let's do

another example we're going to calculate

this third number which is the cost of

the products plus shipping feel free to

pause the video if you want to try it

yourself first otherwise we'll do it

together let's go back to our

console and we're going to add the cost

of the products again which is

$10.90 * 2 plus

$20.95 but this time we're going to add

the cost of shipping which is

$4.99 so

4.99 and press and

enter the computer will do this

calculation and give us this number

which matches what we see in the final

project next we're going to learn a very

important feature of math called the

order of

operations adding subtracting

multiplying and dividing these are

called operations and the characters in

the middle are called

operators now there's a certain order

that we do these operations for example

if we go back to our console and type

the calculation 1 + 1 * 3 and press

enter notice that it multiplies 1 * 3

first which equals 3 and then adds 1

which equals

4 notice that it does not add 1 + 1

first

which equal 2 and then 2 * 3 =

6 the way math normally works is that

multiply and divide are done first add

and subtract are done after this is

called the order of operations and

JavaScript follows the same rules

multiply and divide are done first add

and subtract are done after the order of

operations is also called operator

precedence in

JavaScript one thing to note is that

multiply and divide have the same

priority so if we have both in a

calculation it will calculate from left

to right add and subtract also have the

same priority if we have both in the

calculation it will also calculate from

left to right another feature of the

order of operations is that we can use

brackets to control which part of the

calculation gets done first for example

let's type out this calculation again 1

+ 1 * 3 but this time we're going to add

an Open

Bracket and a Clos bracket around 1 + 1

if we press

enter now the calculation inside the

brackets will be done first so it will

add 1 + 1 = 2 and then 2 * 3 = 6 so when

we use brackets JavaScript will always

do the calculation inside the brackets

first and then do the rest of the

calculation brackets have the highest

priority in the order of

operations now let's learn the syntax

rules for brackets

so we just have to have a matching Open

Bracket and close bracket so something

like this doesn't work because we have

two Open brackets and no Clos bracket we

also need to have a complete calculation

in the brackets so this also doesn't

work because 1 + 1 multiply is not a

complete

calculation now let's do some practical

examples using the order of

operations first we're going to do some

more setup in the final project so we're

actually going to remove all the

products in our

cart and then once our cart is empty

we'll go to the homepage by clicking the

top

left and this time we're going to add

some new products so we'll add one

basketball and two T-shirts

now let's go back to our cart by

clicking the top

right we'll scroll down and we're going

to calculate the numbers in this section

again let's calculate this number at the

top which is the cost of the products

we'll go back to our

console and add the cost of the

basketball which is

$20.95 Plus the cost of the

t-shirts which is

$799 and we have two of them so we'll

multiply this by two if we press

enter this will give us the number that

we see in the final project here notice

that in this calculation we're taking

advantage of the order of

operations even though multiply is

written last

we still multiply these two numbers

first so we calculate the cost of two

T-shirts first and then we add the cost

of the basketball

after okay now let's try something a

little more difficult we're going to

learn how to calculate this 10% tax here

so how do we calculate 10% of something

unfortunately we can't just multiply by

10% in JavaScript instead

we have to calculate the percent

manually so how do we do that 1% is

actually equal to 1 / 100 that's what

percent means so 10% is equal to 10 /

100 which equals

0.1 so to calculate 10% manually we just

multiply this number by

0.1 so we'll type 30 3

6.93 multiplied by 10% or

0.1 if we press

enter it will give us a number that is

close to what we have in the final

project it's the same amount of money

but our number is more accurate than we

need so later in this lesson we'll learn

how to round this number down to exactly

what we have on the web page for now

let's do some more practice with the

order of

operations let's calculate the tax again

except instead of using the final number

36.9 3 Let's calculate this number

individually like here so at the bottom

we're going to add the cost of the

basketball

20.95% 2 and then multiply this by the

tax percent time

0.1 and press

enter unfortunately this number doesn't

match what we got up here and that's

because if we look at this calculation

according to the order of operations

multiply is done first so it will

multiply these three numbers first and

then add 20.95%

after however this is not what we want

we actually want to calculate this

number first this is the cost of the

products so how do we get the computer

to calculate this first and then

multiply by the tax percent

0.1 to do this we can use brackets to

control which part of the calculation

gets done first so let's create this

calculation again 20

.95 +

7.99 * 2 but this time we're going to

add brackets around this part of the

calculation to make sure that this gets

calculated first and then at the end

we'll multiply it by the tax percent

0.1 and now if we press

enter we will get the same number that

we had before

so that's how we use math and the Order

of Operations to calculate the numbers

in this section of the final project so

don't worry you don't have to be good at

math to learn JavaScript this is just to

show you how math Works in

JavaScript in the rest of this lesson

we're going to learn some more details

about numbers and math the first detail

we're going to learn is a weird behavior

of math in JavaScript

first we'll need to learn some

terminology in programming whole numbers

like 2 3 and 4 are called integers

decimal numbers like

2.2 and 2.5 are called floating Point

numbers or floats and unfortunately

computers have a problem working with

floats for example if we go back to our

console and type the calculation

0.1 plus

0.2 and press

enter it will give us this weird number

here that's close to 0.3 but a little

bit

inaccurate so this problem is not

specific to JavaScript many programming

languages also have this problem the

reason this happens is because of how

computers store numbers I'll give a

simplified explan

computers can only store zeros and ones

while humans can count from 0 to 9 so

there's sort of a mismatch between our

number systems for integers this is not

a problem the computer can just use a

bunch of zeros and ones to store it

however for decimal numbers or floats

sometimes the computer can't store the

number properly for example here's how

the computer computer tries to store

0.2 using only zeros and ones at the top

is what the computer stores at the

bottom is what this is equal to in human

numbers we can see that the computer

gets closer and closer to 0.2 but never

actually reaches it and this is why we

get these inaccuracies when calculating

with floats because computers can't

store some floats properly note that

this doesn't happen with all floats for

example computers can store

0.25 without any problems so these

inaccuracies only happen with some

floats but not all of them however when

calculating money we definitely want to

avoid any inaccuracies so let's learn

how to do that first we're going to set

up our cart again so make sure in your

cart you have one basketball with free

shipping and this time you have one

t-shirt so we're going to click

update change this to one and click

save and this t-shirt also has free

shipping now let's scroll up and we're

going to calculate this number at the

top again which is the cost of the

products let's go into our

console and we're going to add the cost

of the basketball

$20.95 plus the cost of the

t-shirt which is

$7.99 if we press

enter calculating with these floats

causes the inaccuracies that we saw

earlier so how do we avoid this problem

the best practice when calculating money

is to calculate in cents instead of

dollars so instead of

$20.95 we're going to calculate

2,95 plus

$7.99 notice we're not using floats

anymore so we avoid the

inaccuracies but now this number is in

cents so we need to convert back to

Dollars to do that we'll surround this

calculation with brackets to make sure

we calculate this first and then at the

end we'll divide by 100 to convert back

to dollars because there are 100 cents

in each dollar if we press

enter and scroll

up that's how we get the exact number

that we see on the page so remember in

programming calculations with floats are

sometimes inaccurate and when working

with money the best practice is to do

the calculation in cents and then

convert back to dollars at the

end the next detail we're going to learn

is how to round a number in JavaScript

rounding just means taking a number and

moving it to the nearest integer to

round a number we can use this

code capital m

math. round Open Bracket close bracket

so make sure you use a capital M because

JavaScript is case

sensitive now between the brackets we

can put a number that we want to round

like

2.2 if we press enter it will round this

number down to

two if we do capital M math do round

Open Bracket close bracket and between

the brackets we put

2.8 and press

enter it will round 2.8 up to three now

let's do a practical example with

math.round we're going to calculate the

tax again but this time we're going to

round the result to exactly this number

on the page so first let's calculate the

tax we'll go into our

console and add the cost of the product

products in cents so

2,95 for the

basketball and plus the cost of the

t-shirt which is

$7.99 and we'll surround this in

Brackets to make sure we calculate this

first and then we're going to multiply

this by the tax percent or

0.1 and finally we'll convert this back

to dollars so let's surround this in

Brackets as well to make sure we

calculate this first and at the end

we'll divide by 100 to convert back to

dollars so notice here we can have

brackets inside brackets in this

situation JavaScript will calculate the

inner brackets first and then the outer

brackets and then everything else if we

press enter

here this gives us

2.89 which is close to the number on the

page it's the same amount of money but

our number is more accurate than we need

so now let's learn how to use math.round

to round this number to exactly

2.89 first let's create a copy of this

calculation so we'll select it right

click copy

and down here right click and

paste by the way if you paste in the

console you might see this warning

message to fix this you can type allow

pasting and press enter and now you can

paste so let's continue and we were

trying to round 2.89 4 to exactly

2.89 so one thing we might try to do is

to round this entire

calculation however this will round 2.89

4 to 3 because it rounds to the nearest

integer instead what we want to round is

this number here so remember that this

number is the result in cents which is

289.50

if we round this number it will round

down to

289 which is exactly

$289 so to round this calculation at the

front we'll type capital M

math.round so we already have brackets

around this so we don't need extra

brackets so this this will round to

289 and finally we'll convert this back

to dollars at the End by dividing by 100

if we press

enter that's how we rounded this

calculation to get the exact number on

the

page so to summarize we first calculate

the result in cents and then we round

this to the nearest scent and then at

the end and we convert back to

Dollars again don't worry you don't have

to be good at math to learn JavaScript

these examples are just for learning

almost all the math we do in JavaScript

is more simple than this I'll give you

some exercises at the end of this lesson

to help you get more practice the last

thing we're going to learn in this

lesson is how to use Google when you're

learning to code so far I've been giving

you different pieces pces of code like

alert and

math.round you might be wondering where

do I find this code these pieces of code

are features of JavaScript and I find

this code by searching on Google so

we're going to learn how to use Google

to learn new features of JavaScript on

our own let's go to our browser and

create a new tab at the

top and we'll click here and type

google.com and press

enter and we'll search in Google so the

trick to searching in Google is to

search for what we are trying to do for

example if we want to round a number we

would search for

JavaScript how to round a

number if we press enter

sometimes you might get the code right

away in the first result and sometimes

you might have to go into the other

results to find the code that you need

in my example I see the code math.round

in the first result so I can click into

this result read about what this code

does and also see some examples of how

to use it one thing to keep in mind is

that when you're searching in Google you

might not understand understand all the

code that you get in your results for

example here there's a lot of code that

we haven't learned yet and actually

that's okay we just need to look for the

pieces of code that look familiar to us

like this part of the code we can then

use this part of the code in our own

code we don't have to understand every

bit of code that we get from Google and

don't worry as we move through this

course we we will understand more and

more of this code that we get from

Google

results these days we also have some

artificial intelligence or AI tools that

can help us search for code I'll provide

links to some of these tools in the

video

description by the way to find the links

mentioned in each lesson you can click

here in the

description and this page contains all

the links mentioned in each

lesson and that's the end of this lesson

in this lesson we learned how to work

with numbers and math we learned the

order of operations and brackets we

calculated the numbers in the final

Amazon Project we learned that

calculations using floats can be

inaccurate and how to avoid this problem

when working with money we learned how

to round numbers using

math.round and we learned how to search

for code on our own here are some

exercises to help you practice numbers

and math

in the previous lesson we learned how to

work with numbers and math in this

lesson we're going to learn how to work

with text and we're going to create the

text in this section of the final

project first make sure you have the

final project open and you're on the

checkout page also make sure you have

the console open on this page if not you

can go to a blank area

right click click

inspect and then click the

console now we're going to learn a

feature of JavaScript called strings a

string represents text let's go to our

console and create our first string

we're going to type single quote hello

and single quote and press

enter this is a string and it represents

the text hello and we've actually seen

this code before in the first lesson the

first piece of code that we learned was

alert Open Bracket single quote hello

single quote close bracket and

semicolon this code creates a popup on

the page if we press

enter it creates a popup now in inside

these brackets we actually created a

string this string is the text that

appears in the popup so as you can see a

string represents

text let's press

okay and now let's learn the syntax

rules for strings to create a string we

just write some text like hello and then

surround this text with single quotes

one at the beginning and one at the end

we can also add strings together for

example let's type the string

sum plus the string

text and press

enter when we add two strings it

combines the strings together into a

bigger string and this makes sense we're

adding two pieces of text together we

can also add more than two strings at a

time

for example we can type the string

sum plus the string

more plus the string

text if we press

enter the computer will combine all

three strings into one big string by the

way this is called concatenation when we

combine strings together now in in the

previous lesson we learned about numbers

numbers and strings are two different

types of values in JavaScript they

represent different things and we can

actually check what type of value

something is using this code type of and

then space and then a value like the

number two if we press

enter type of will tell us that two

is a number if we do type of quote hello

quote and press enter it will tell us

that hello is a

string now what if we added a string and

a number together for example let's type

the string

hello plus the number three and press

enter

so when we add a string and a number

JavaScript will automatically convert

this number into a string so this gets

converted into the string hello plus the

string

three and then it combines them together

into the string hello 3 this feature is

called type coersion or automatic type

conversion okay now that we understand

understand the basics of strings let's

do some practical examples we're going

to use strings and numbers to create the

text in this section of the project

first make sure that in your cart you

have one basketball with free shipping

and you have one t-shirt also with free

shipping and you have no other

products let's scroll up and we'll start

by creating this text in the top right

so this is the cost of the products but

this time we're going to have a dollar

sign so instead of just a number this

will be

text so one thing we can do to create

this text is just type out the string

directly like quote doll

28.94 and

quote however let's actually calculate

this number using math

remember the advantage of JavaScript is

that it's able to do

calculations so instead of typing out

28.94 we're just going to create the

string Dollar Sign Plus and we're going

to calculate this number using math so

we're going to add the cost of the

basketball which is

$2.95

plus the cost of of the t-shirt which is

$7.99 if we press

enter unfortunately this doesn't look

right instead of doing math and adding

these two numbers together it just sort

of put the numbers one after another

into the string so why is this happening

JavaScript adds from left to right so

the first step is to add these two

values and as we learned if we add a

string and a number JavaScript will

automatically convert this number into a

string so the result of this calculation

will be the string doll

2.95 and

quote the next step is to add

7.99 so it will add

7.99 and now we're adding again a string

and a number

so JavaScript will automatically convert

this number into a string and combine

them together that's why it puts

7.99 at the end of this string instead

of doing

math so what we actually want to do here

is to add these two numbers first and

then combine the total with the string

so how do we do this the solution is

that strings also follow the order of

operations just like numbers and

remember in the order of operations we

can use brackets to control which part

of a calculation gets done first so

let's type this calculation out again

the string Dollar Sign Plus 20.95%

close bracket around this

calculation this tells the computer to

calculate this number first using math

and then combine this result with the

string after if we press

enter now this is doing math and it

solves our original problem

unfortunately now we have another

problem this math is inaccurate so

remember from the previous lesson doing

calculations with floats can sometimes

cause

inaccuracies and the best practice when

calculating money is always calculate in

cents and then convert back to dollars

at the end so at the bottom here we're

going to add the string

Dollar Plus open bracket and instead of

$20.95 we're going to add

2,95 Plus

$7.99 and close bracket and then at the

end we're going to convert this number

back to Dollars by dividing by 100 if we

press

enter this will give us the text that we

see in the final

project again strings follow the same

order of operations as numbers brackets

are always calculated first multiply and

divide are done next and add and

subtract are done after so adding this

result to the string is the last

step now let's do a more complicated

example let's use strings and numbers to

create this entire line of text not just

the dollar text to create this we're

going to go from left to right let's go

back in our console and we're going to

start with the string

items Open Bracket and here we could

just type two and close bracket but

let's actually calculate this number as

well using math so this number is the

quantity or the number of products in

our cart let's go back to our console

we're going to end the string here and

we're going to add and we're going to

calculate the quantity

so we have one basketball plus one

t-shirt again we run into the same

problem as before this gets calculated

first and results in a string and then

it will just combine the one at the end

of the string instead of doing math to

solve this we're going to use brackets

again so around the 1 + 1 we're going to

add Open Bracket and close

bracket this tells the computer to add

the numbers first and then combine it

with a

string all right let's keep going from

left to right we're going to add the

rest of the string quote close bracket

colon and let's just use a space to

represent the space between these two so

we'll type a space dollar sign and then

we're going to calculate this number

again and add it to the string so we'll

end the string and then plus and we

already did this calculation up here so

we can select this and then

rightclick

copy and here right click and

paste and press

enter by the way if you paste in the

console you might see this warning

message

to fix this you can type allow

pasting and press

enter and now you can

paste and that's how we create this

first line of text using strings and

numbers we break up the string into

Parts calculate the numbers and then add

the parts back

together all right now let's take these

strings that we created Creed and do

something with them let's create a popup

and display this first line of text

inside the popup we'll go back to our

console and type the code for creating a

popup

alert Open Bracket close bracket

semicolon and then inside the popup

we're going to display this string so

let's just make a copy of this code

we'll select it right click

copy and between the brackets right

click and

paste if we press

enter the computer displays a popup with

the first line of text of the final

project

inside so that's how we use strings to

create the text in the final project and

once we create the strings we can use

them in other JavaScript

code in in the rest of this lesson we're

going to learn more details about

strings in JavaScript there are actually

three ways to create a string the first

way is to use single quotes which we

already learned for example we can type

single quote hello and single quote and

press

enter the second way to create a string

is to use double quotes for example

double quote hello and double quote and

press

enter this creates the exact same string

as single quotes so which one should we

use to create a string single quotes or

double quotes in JavaScript I recommend

using single quotes by default they're a

little easier to read and type there is

one situation where double quotes might

be useful and that is is if we have a

single quote inside the string for

example if we type the

string I'm

learning

JavaScript and single quote and press

enter this doesn't work because there's

a single quote inside the string and

this single quote will end the string

early to solve this we can create the

string using double quotes for example

double quote I'm

learning

JavaScript and double quote and press

enter so now this works because we

created the string using double quotes

the single quote no longer has a special

meaning and it will no longer end the

string early so this is a situation

where double quotes might be useful

otherwise we use single quotes by

default now there's actually another

solution to this problem other than

using double quotes and that's by using

an escape character so a character is

one letter number or symbol in a piece

of textt for example the text hello has

five characters h e l l

o a character can be a letter in number

or also a symbol these are all

considered

characters now in addition to these

characters we have a special set of

characters we can also use in a string

called Escape characters an escape

character looks like this a backslash

and then another character like single

quote this combination actually counts

as one character in a string this

character creat creat a single quote

that is just text it doesn't have a

special meaning and it doesn't start or

end strings for example we can create

this string with single quotes again so

single quote I and this time we'll use

the Escape character back slash single

quote and then M

learning

JavaScript and single quote and press

enter and now this works because the

Escape character back SL single quote

creates a single quote that is just text

it doesn't start or end the

string another Escape character that's

useful to know is back SL double quote

this creates a double quote that is just

text it doesn't start or end a

string the last Escape character we'll

learn in this lesson is back

sln this is called the new line

character this Escape character doesn't

create the letter N anymore it creates a

new line of text for example let's

create a popup using

alert Open Bracket close bracket and

semicolon and then inside the brackets

we're going to create a string sum and

then back

sln text and single quote if we press

enter you'll notice that this Escape

character created a new line of text in

the popup and that's why we call this

the new line character so that's how

Escape characters work they are a set of

special characters that start with back

slash and we can use them in a

string now let's press okay

and we're going to learn the Third Way

of creating a string in JavaScript which

is using back ticks for example let's

type in our console and we'll type

backtick hello and backtick and press

enter this creates the same string as

single quotes and double quotes strings

created with backx actually have a name

we call these template strings and they

have a name because they have some

special features the first special

feature of template strings is called

interpolation interpolation lets us

insert a value directly into a string

for example let's say we want to create

the first line of text in our project

earlier in this lesson we created this

text with concatenation which means we

broke it up into parts and added them

back together in interpolation gives us

a much easier way to do this we'll go to

our console and we'll create this text

using a template string because

interpolation is only a feature of

template strings so we'll type backtick

items Open Bracket close bracket and

back tick and now between these brackets

we want to insert the quantity or the

number of products in our cart to insert

this with interpolation we're going to

type Dollar open curly bracket close

curly bracket so this combination of

characters allows us to insert values

directly into the string between these

curly brackets we can calculate the

quantity which is one basketball plus

one

t-shirt this will add 1 + 1 which equals

2 and then insert it directly into the

string

let's keep going and create the rest of

this line so we're going to type at the

end a Colin space and dollar and now

we're going to insert another value into

the string which is the cost of the

products to insert another value we're

going to type Dollar open curly bracket

close curly bracket again in between the

curly brackets we're going to calculate

the cost of the products

which is

2,95

plus

$7.99 and we'll surround this in

Brackets to make sure we calculate this

first and at the end we're going to

convert back to Dollars by dividing by

100 if we press

enter this creates the first line of

text again in our final project

if we compare this code which uses

interpolation to our previous code which

uses concatenation you can see that

interpolation is a much cleaner way of

inserting values into a string so

interpolation is a recommended

solution next template strings have

another special feature called

multi-line strings let's go to our

console and we're going to type a

backtick

sum and then press

enter and text and back tick notice that

this string is on multiple lines so we

call this a multi-line string and this

feature is only available for template

strings if we press

enter you can see that the new line in

the string just creates the new line

Escape character that we learned earlier

so that's the multi-line string feature

of template strings we're going to use

multi-line strings a lot later in this

course but for now I just wanted to

introduce you to this feature now you

might be wondering again what should we

use to create a string single quotes or

template strings even though template

strings have more features I find that

most JavaScript code still uses single

quotes by default so my personal

recommendation is to use single quotes

by default and if we need to insert a

value into the string or type the string

on multiple lines then use template

strings and that's the end of this

lesson in this lesson we learned about

strings a string represents text we

learned how to use strings and numbers

to create the text in our final project

we learned three different ways of

creating a string single quotes double

quotes and back ticks or template

strings we learned about Escape

characters and we learned two useful

features of template strings

interpolation and multi-line

strings here are some exercises to help

you practice working with strings

so far in this course we've learned some

basic features of JavaScript like

numbers and strings in this lesson we're

going to learn how to use HTML CSS and

JavaScript together because as I

mentioned at the beginning of this

course we use all three Technologies to

build build a full

website HTML creates the content of a

website like the buttons and the text

CSS changes the appearance of the

website and JavaScript makes the website

interactive the first thing we're going

to do is review the basics of HTML and

CSS that we will need for the rest of

this

course now in order to write HTML and

CSS code we need to install another

piece of software called a code editor a

code editor helps us write and organize

our code the most popular code editor

for web development is called vs code or

Visual Studio code to install vs code

you can go to google.com in your

browser search for VSS

code click the result

and follow the instructions to download

and

install once we've installed VSS code

we're ready to review the basics of HTML

and

CSS we'll start with

HTML HTML stands for hyper text markup

language and just like JavaScript HTML

is also giving instructions to a

computer now unlike JavaScript we can't

use the console to write and run HTML

code instead we write HTML code inside a

file using our code editor let's do that

right now we'll start by going to our

desktop so I'm going to close my browser

to go to my

desktop and then we're going to create a

new folder so we can right click new

folder this folder is going to contain

all the code that we write in this

course let's name this folder JavaScript

dasc next we're going to open this

folder in our code editor so let's open

vs

code and then we'll click

file open

folder and find the folder that we just

created for me it's on the

desktop and it's this folder right right

here so we're going to select the folder

and then click select

folder now we can close this startup

message and we're going to create an

HTML file we're going to click this icon

to create a new

file and we're going to name this file

website do

HTML and press

enter ending the file name name with

HTML tells a computer that this file

contains HTML code rather than just

text now let's review some basic HTML

code we're going to type the code less

than button greater than and we also

need to type less than slash button

greater than but our code editor might

autocomplete this for us so this code

tells a computer to create a button and

inside the button we're going to have

the text

hello now let's save this file by

clicking

file

save or by typing contrl s on Windows or

command s on

Mac now to run this HTML code we're

going to open this file in our browser

let's go back to our desktop

we're going to open the folder that we

created find the HTML file select it and

then right click open with Google

Chrome as you can see we have a website

and we created a button with the text

hello inside and if we look back at our

code that's exactly what we told the

computer to do

so just like JavaScript HTML is also

giving instructions to a

computer let's review some more HTML

code first I'm just going to rearrange

my windows here so that it's easy to see

the website side by

side next we're going to click the end

of the first line and press enter to

create a new line and we're going to

type the code less than P greater than

and we also need to type less than SLP

greater than so this code creates a

paragraph and inside the paragraph we're

going to put some text for example

paragraph of text now let's save our

file by typing contrl s on Windows or

command s on

Mac and to update our website to the new

code we're going to go to our website

and click refresh or typ controlr on

Windows or command r on

Mac and now you can see that the

computer created a paragraph of text

just like we told it to do and that's

the basics of HTML the computer reads

our code and then follows our

instructions one by one first it creates

a button and then it creates a paragraph

of text

now let's review the syntax rules for

HTML each of these things that were

displaying on a web page these are

called HTML elements so a button is a

type of HTML element and a paragraph is

another type of HTML element to create

an element we start with a less than

symbol and then the element name like a

button and then the greater than symbol

so this whole thing is called an HTML

tag this tells a computer to create a

button

element every HTML tag needs a matching

tag the matching tag follows the same

syntax except it has a slash in front of

the element name so this is called the

opening tag and this is called the

closing tag you can think of the opening

tag as the start of the button and the

closing tag tag as the end of the button

and in between we have the contents

inside the button in this case it's the

text

hello in addition to text we can also

have elements inside an element for

example we can go to our paragraph

element and we can add a button inside

so less than button greater than and we

also need less than SL button greater

than and then inside the button we'll

also have the text

hello if we save this file and refresh

the

page now our paragraph element has a

button element

inside by the way this is called nesting

when we have an element inside another

element the last syntax rule we have to

review is that in HTML if we have

multiple spaces for example if we go

here and type multiple

spaces multiple spaces are combined into

one space on the web page so if we save

this code and

refresh you'll notice that all of the

spaces that we added only show up as one

space on the web page in addition in

HTML new lines also count as spaces so

if we go back to our

code and we type here and press enter to

create a new line and then save and

refresh notice that the new line doesn't

appear on the web page and that's

because this new line here is the same

as spaces in HTML so all of these get

combined into one space on the web

page at first this might seem a little

weird but this feature gives us a lot of

flexibility when organizing our h ml

code for example we can go into our code

and add a new line here to separate

these two elements and make our code

easier to read another thing we usually

do to make our code easier to read is to

put the contents of an element on its

own line for example we're going to type

here and press enter and here and press

enter

again to put the contents of the button

Buton on its own line now it's a lot

easier to see where this button starts

and where it ends we can do the same

thing with the paragraph We can type

here and press enter and type here as

well and press enter and then remove

some of the Extra

Spaces to put the content of the

paragraph on its own line and now if we

save our

file and refresh

you notice that none of the new lines

that we added appear on the web page by

the way a web page is a single page like

the homepage or the cart page together

we call this a

website so that's the basics of HTML and

HTML

syntax now let's review CSS CSS stands

for cascading style sheets and CSS

changes the appearance of our website

let's review some CSS code we're going

to write our CSS code inside our HTML

file first let's type here and create

some new lines at the top and then at

the top we're going to create a special

HTML element called the style element so

let's type less than style greater

than and we also need the closing tag

less than SL style greater than so the

style element is unique because it

doesn't appear visibly on the page

instead the purpose of the style element

is that it lets us write CSS code

inside so inside here let's press enter

to create a new line and we're going to

type

button open curly bracket close curly

bracket and then inside the curly

brackets we're also going to press enter

to create a new line so this is CSS code

and this code tells a computer to change

the appearance of all buttons on the

page and then inside these curly

brackets we can tell the computer how to

change the appearance for example we can

type

background- color colon red and

semicolon if we save

and

refresh you can see that this CSS code

changes the appearance of all buttons on

the page and changes their background

color to

Red let's do another example we're going

to go back to our CSS code going to type

here and press enter to create a new

line and we're going to add color colon

white and semicolon let's save

and

refresh and this CSS code changes the

text color of all buttons on the page to

White let's do one more example we're

going to type the

code order Colon none and

semicolon let's save this and

refresh and this CSS code removes the

border for all buttons on the page

and that's how CSS works we tell the

computer which elements we want to

change and then how to change the

appearance of these

elements now let's review the syntax

rules for

CSS this part of the CSS code is called

the CSS selector it tells a computer

which elements we want to change in

other words it selects which elements to

change inside the curly brackets we have

some CSS Styles this tells a computer

how to change the

appearance for each style the left side

is called the CSS property this tells a

computer what we're changing the right

side is called the CSS value this tells

a computer what we're changing the

property to for example this style

changes the background color to

Red we use a colon to separate the

property and the value and a semicolon

at the end to tell the computer that

this is the end of a style so that's the

basic syntax of CSS we tell the computer

which elements we want to change and

then how to change the appearance of

these

elements the next thing we're going to

review is HTML

attributes right now this CSS selector

changes the appearance of all but

buttons on the page however what if we

only want to change the appearance of

this one button and we want to style the

other button differently how do we do

that we're going to review a feature of

HTML called attributes attributes change

the behavior of an element for example

we're going to go to the opening tag of

the first button and then here we're

going to add an HTML attribute by typing

space

title equals double quotes and then in

between the double quotes we're going to

type tool

tip so this is an HTML attribute and

this attribute adds a tool tip to this

button if you're wondering what a tool

tip is if we hover over some code in our

code editor it'll show us this sort of

popup with more

information this is called a tool tip

when we hover over something and this

shows up so if we save our

file and refresh the web page and now we

hover over our button we can see that

the HTML attribute added a tool tip to

our button and then inside the double

quotes is the text inside the tool tip

for example we can actually change this

to good

job and if we save save and

refresh and hover over our button the

text between the double quotes is what

shows up in our tool tip so that's an

example of an HTML

attribute now let's review the syntax

rules for

attributes we always put attributes on

the opening tag and we add a space

between the element name and the

attribute to separate them on the left

side is the attribute name this tells

the computer what we're changing about

this element on the right side is the

attribute value this tells a computer

what we're changing this attribute to

for example here we're changing the tool

tip of this element to good job we

separate the name and value with an

equal sign and make sure there are no

spaces around the equal sign and we

surround the value with double quotes

now let's go back to the original

problem how do we style these buttons

differently we can do this using a very

important attribute called the class

attribute let's review that right now

we're going to go back to our button and

then here we're going to type space

class equals double quotes and then

inside the double quotes we're going to

type red Das

button so the class attribute sort of

adds a label to an element so here we

labeled this button as a red button and

now that we labeled this element we can

select it in

CSS to do that we're going to go to our

CSS code we're going to remove the

button

selector and replace it

witht

red-

button when we start the selector with a

DOT this means that now we're looking

for a class so here we're going to look

for all elements with the class red dash

button which is only this element if we

save and

refresh now only the elements with the

class red button gets these Styles we

can also add the same class to multiple

elements for example we can go to to our

other

button and add the class equals

red-

button if we save and

refresh now these Styles get applied to

both buttons again because they both

have the class red-b button if we want

to style this button differently we just

give it a different class for example we

can change this to Yellow yellow dash

button and then in our CSS we can add

another selector so we can type dot this

means we're going to select a class and

we're going to select the yellow Das

button class open curly bracket close

curly bracket and then inside here we

can add some styles for the yellow

button for

example background Das color colon

yellow and

semicolon now let's save and

refresh and that's how we use the class

attribute in HTML to modify specific

elements the final thing we need to

review is something called the HTML

structure let's go back to our website

we're going to find a blank area and

then

rightclick and then click inspect

so we already learned about the console

tab here we can write and run JavaScript

code now we're going to go to the

elements tab which is for HTML and CSS

so in the elements tab we can see all

the HTML on the page as well as all the

CSS on the page and we can play around

with the CSS if we

want now if we go back to to the

HTML you'll notice that our web page has

some elements that we didn't add before

the HTML element the head element and

the body

element so this is the structure that

we're supposed to follow when writing

HTML in our code we didn't follow the

structure so the browser actually adds

it for us

automatically however it's still best

practice to follow this structure in our

code because it gives us access to some

more features of

HTML let's review the HTML structure and

add it to our

code we're going to type up here and

we're going to create some new

lines and now every HTML file is going

to start with less than

exclamation dock type in capitals and

then space

HTML and greater

than this is not an HTML element it's a

special line of code that tells a

browser to use a modern version of

HTML if we don't have this the browser

might fall back to an older version of

HTML that has less

features next we're going to create an

HTML element so less than

HTML and greater

than the HTML element represents the

entire web page

so everything on the web page should go

inside this

element and then inside the HTML element

we're also going to split it up into two

sections the head

element and the body

element so the body element is supposed

to contain everything that is visible on

the page in our example that would be

the buttons and the parag graph so let's

actually select this

code and we're going to

rightclick and

cut and then inside the

body we're going to right click and

paste the head element contains

information about the page in general

everything that is not visible on the

page goes inside the

head in our examp example that would be

the style element so let's select this

as

well we're going to rightclick and

cut and then inside the

head we're going to right click and

paste and at the bottom let's just clean

up by removing all of the extra new

lines so this is a structure that we're

supposed to follow in all of our HTML

files as you can see this structure uses

a lot of nesting or elements inside

elements to organize our

code okay so what are the benefits of

following this structure one benefit is

that there are other elements that we

can use inside the head for example

let's type here press enter and we're

going to add the title element so the

title element sets the text in the

tabs inside we can type HTML CSS review

if we save and refresh the title will

show up in the

tab so this is an example of an element

that we can now add in the

head another benefit that we get from

this structure is the ability to

automatically refresh our web page when

we change our code

so far every time we change our code we

have to save and then manually refresh

the web page we can actually automate

this by following the structure and then

installing a VSS code

extension so let's click the extension

area and we're going to search for the

extension live

server and click install

once we have that installed we're going

to change a

setting let's open the settings by

clicking this icon in the bottom left

and then click

settings at the top we're going to

search for live

server and we're going to look for a

setting called live server custom

browser and we're going to change this

to

Chrome now now if Google Chrome is

already your default web browser you

don't need to do this step but it's nice

to

know now let's close the

settings and go back to our

code next instead of opening this file

directly in the browser like before

we're going to use live server to open

this file to do that we're going to

rightclick this file in our code editor

and then click open open with live

server if we open a file with live

server this web page will automatically

refresh when we change our

code for example we can go here and

change the background color to Green if

we save live server will automatically

refresh the web page so we don't have to

do that back and forth

anymore let's just change it back to Red

so that the class last name makes sense

and

save and we can also close the previous

tab so this is the HTML structure it

gives us access to more features of

HTML and this is all we need to review

about HTML and CSS for now if you want

to learn more you can check out my HTML

and CSS full course in the video

description by the way to find the links

mentioned in each lesson you can click

here in the

description and this page contains all

the links mentioned in each

lesson before we add JavaScript to our

website we're going to review some VSS

code

setup so you'll notice that many of

these lines have spaces at the front

these spaces are called in indents and

indents make our code easier to read for

example we can easily tell that this

code is inside the brackets because it

has an extra indent in the

front if we didn't have indents here's

what the code would look like it's a lot

harder to

read to add an indent we can type at the

beginning of the line and press

tab to remove an indent we can press

shift tab or just use

backspace now by default VSS code uses

four spaces per indet however in HTML

CSS and JavaScript we usually use two

spaces per indet so we're going to

update this setting let's go to our

settings by clicking this icon in the

bottom

left and then click

settings and at the top we're going to

search for tab

and we're going to change the tab size

from 4 to

2 now let's close the

settings and we're also going to change

the indents for this file we're going to

go down here and click select

indent and we're going to choose indent

using

spaces and then click

two and now if we type at the start of a

line and press tab it will only add two

spaces per

indent so let's reformat our code to use

two spaces per indent instead of four

first we're going to remove all the

indents in our code a shortcut for this

is to select all of these

lines and press shift tab to remove one

indent for each line so we're going to

keep pressing shift tab until we remove

all the

indents next next we're going to add the

indents back using a similar shortcut

we're going to select the head

element and press tab to add one indent

for each line and then select everything

inside the head and press tab to add

another indent and then select

everything inside style and press Tab

and then inside each of these brackets

we're going to select the lines press

Tab and then here press tab we'll do the

same thing for the body element we'll

select all these lines and press tab

we'll select everything inside the body

press Tab and then inside each of these

elements we're going to press Tab and

press

tab now if we save our website will look

the same because all we did was adjust

the

indents so there's one other setting in

vs code that we're going to set up which

is line wrapping if you look at this

line of code you can see that it's

really long and we need to scroll

horizontally to see the rest of the line

instead we're going to make this line

wrap around if it gets too long let's go

back into our settings by clicking here

and then click the

settings and then up here we're going to

search for

wrap and we're going to look for editor

word wrap and we're going to turn this

on now if we close our settings and go

back to our

code this line which is really long will

wrap around to the next line instead of

us having to horizontally

scroll so that's the vs code setup that

we need two spaces per indent and line

wrapping finally we're going to add

JavaScript to this website so we learned

that we can use the console to write and

run JavaScript well there's actually

another way to run JavaScript which is

inside an HTML file let's learn how to

do that so we learned that HTML has a

special element that runs CSS code

called the style element while HTML has

another special element that runs

JavaScript code and this element is

called the script

element so inside

body at the bottom of the body we're

going to add less than script greater

than and the closing tag less than SL

script greater than and inside the

script element we can put some

JavaScript code we're going to add the

code alert Open Bracket quote hello

quote close bracket and semicolon if we

save

live server will refresh the page and

now you notice that the computer now

runs our JavaScript code just like it

did in the console it creates a popup

with the text hello

inside and we usually put the script

element at the bottom of the body

because we want the web page to be

created first and then we use JavaScript

to make it

interactive for the rest of this course

we're going to run our JavaScript code

using using an HTML file the console

that we used in the previous lessons is

more of a way to try out JavaScript code

we wouldn't use a console for a real

website in addition to the script

element we have another way to run

JavaScript code inside HTML and that's

by using an attribute let's go back to

our first button and here we're going to

add another attribute so let's type

space and this time we're going to add

the

onclick attribute equals double

quotes So this attribute will run

JavaScript code whenever we click this

button that's what onclick means between

the double quotes we can write some

JavaScript for example let's press enter

enter and then here we're going to type

alert

Open Bracket

quote good job quote close bracket and

semicolon now if we

save live server will refresh the page

and run this line of JavaScript code

let's press okay and now if we click

this

button it will run this line of

JavaScript code and create a popup with

a text good job inside

so those are two places where we can run

JavaScript code the script element and

the onclick attribute the code in the

script element runs first when the page

is loaded the code in the onclick

attribute runs after when we click the

button on the

page and that's how we use HTML CSS and

JavaScript together on a website

notice that everything starts from

HTML HTML first creates the website and

then inside the HTML we can run CSS code

to change the appearance and we can run

JavaScript code to make the website

interactive now let's learn some new

features of JavaScript that we haven't

seen yet in this course the next feature

we're going to learn is called comments

comments are pieces of code that the

computer ignores so let's create our

first comment we're going to go down to

the script element

here and type forward slash forward

slash so this is a comment anything

after the double slash will be ignored

by the computer so we can type anything

we want like this is a

comment if we save it ignores this line

and creates the popup in the next

line now let's close this popup and

learn why we use

comments comments are useful for

providing more information for people

reading our code for example we can

create a comment above this code like

this code creates a

popup this comment helps others and

ourselves understand what this code does

so that's one way we use

comments another way we use comments is

if we don't want to run some code

anymore but we also don't want to delete

it for example this code creates a popup

every time we refresh the page and this

can be

annoying so I want to stop running this

code but I also don't want to delete it

because you might want to review this

code

later so what we can do here is to add a

double slash in front of this line to

turn this code into a

comment now if we save the computer will

ignore this line of code and not create

the

popup this is called commenting out the

code it's useful if we don't want to run

some code anymore but we also don't want

to delete it for informational purposes

so JavaScript has another Syntax for

writing comments and that syntax is

slash star and star

slash here anything between the stars is

a comment this is called a multi-line

comment because between the Stars we can

write a comment on multiple lines for

example we can type multi enter line

Line enter

comment on the other hand double slash

is known as a single line

comment now just like JavaScript HTML

and CSS also have comments but they use

a different

syntax if we scroll up to our

HTML here we can type less than

exclamation

d-h and we also need dh- greater than so

anything between these double dashes is

a comment for example this is a

comment in CSS to create a comment we

can type slash star star slash so it's

the same multi-line comment as

JavaScript between the Stars we can add

a comment so this

is a

comment if we save our

file nothing changes on our web page

because comments are ignored by the

computer the last feature of JavaScript

we're going to learn is called

console.log let's go back to our

code and at the bottom in the script

element we're going to type the code 2 +

2 so we learned that this code in Java

script does some math however if we save

this

file where is the result of this math so

we might think that the result will show

up in the console but if we

rightclick click

inspect and then click the

console you'll notice that the result

doesn't show up here either and that's

because before we were running 2 + 2

inside the console so the result shows

up in the console but now we're not

running this code in the console anymore

we're running this code on the web page

so how do we see this

result the solution is we're going to

redirect this result back to the console

to do that we're going to use this piece

of

code

console.log Open Bracket close bracket

and

semicolon console.log will display

whatever's between the brackets back in

the console so if we move this code

between the brackets so we select this

and then right click cut and then

between the brackets right click paste

and

save the result of this code is

displayed back in the console

and console.log works for any code that

we learned so far for example we can use

strings so let's create a new line and

type

console.log Open Bracket close bracket

semicolon and then between the brackets

let's type some

strings quote Su quote plus quote text

quote

and save this

file again it will display the result of

whatever's between the brackets back in

the

console so that's how we see the result

of JavaScript code that is running in a

file we use

console.log and that's the end of this

lesson in this lesson we reviewed the

basics of HTML and CSS we set up our

code editor vs code we learned how to

load JavaScript inside an HTML file

using the script element and the onclick

attribute we learned how to create

comments and we learned how to use

console.log thanks for watching this

course so far if you want to support

this channel you can check out the

premium version of my courses just like

this one where you can get a certificate

of completion and a learning platform if

you're interested in extra videos from

me more in-depth videos and behind thes

scenes content you can check out these

links here you can also support the

channel by liking the video subscribing

and sharing this video with others

thanks again and let's continue with the

course here are some exercises you can

try on your own to practice what we

learned in this lesson

in this lesson we're going to learn the

next feature of JavaScript called

variables and we're going to use

variables to build a simple version of

the cart quantity feature of the final

project

first let's create a new HTML file just

for learning variables we're going to go

to our code editor and click this icon

to show our files and then click this

icon to create a new

file and we're going to name this file

05-

variables.

HTML and press

enter so the 05 just means that this

file is for lesson

five let's also add the lesson number to

website.

HTML we'll select this file and then

rightclick

rename and then at the front We'll add

04- and press

enter next we're going to copy all the

code in website. HTML to variables.

HTML so let's click in this file and

we're going to select all of this code

by typing control a on Windows or

command a on

Mac and then we're going to

rightclick

copy and then inside variables.

HTML rightclick and

paste let's click this icon to hide our

files for now and we'll prepare this

file for this lesson so let's scroll up

to the top and first we're going to

change the title to

variables next we're going to delete all

the CSS because we're going to start

over and we're going to delete all the

HTML except for the script

element and let's delete all the

JavaScript from the previous

lesson and finally let's save

and we'll open this file in our browser

by right clicking and then open with

live

server and now we can close the previous

tab and the previous code for

now now we're ready to learn

variables first of all what is a

variable a variable is like a container

we can save a value like a number or a

string inside a variable and then then

use it later Let's do an example and

create our first

variable inside the script element we're

going to type the code let and space the

word let creates a new variable and now

we're going to choose a name for our new

variable let's name this variable

one so this creates a variable or a

container named variable one and now we

can save a value inside this variable to

do that we're going to type space equals

space and then a value like a number or

a string so let's save the number three

inside and we'll type a semicolon at the

end so here we use the let to create a

new variable we named this variable

variable one and we saved the value

three inside this

variable now that we saved this value we

can use it later for example let's type

a new line and type the code

console. log Open Bracket close bracket

and

semicolon remember from the previous

lesson that this code displays

whatever's inside the brackets in the

console so far we put a value inside

like the number

two if we save and then go to our

website and open the console so right

click

inspect and then click the

console we can see that the number two

was displayed in the

console so now let's try replacing this

value with the variable that we created

above so instead of two we're going to

console.log variable one

if we

save notice that it now displays three

so it's displaying whatever value is

saved inside the variable as you can see

we can save a value inside a variable

and then use that variable later

on let's do another example we're going

to create another variable so we're

going to create some new lines and we'll

type

let and this time let's name this

variable

calculation and we're going to type

space equals space to save a value

inside this new variable and this time

instead of just a number we're going to

save a

calculation 2 + 2 and semicolon so this

will calculate 2 + 2 and then save the

result which is four into the

variable if we call

console. log Open

Bracket

calculation and semicolon and

save it will show us that the value for

is saved inside

calculation now let's try this code

we're going to type a new line and then

console. log Open Bracket and

calculation again

and plus 2 and

semicolon so here we're using a variable

inside a

calculation what this does is that it

takes whatever value is saved inside the

variable right now it is four and then

substitutes that value into the

calculation so this will be 4 + 2 which

equals

six if we

save we can see that in the console it

display blade

six so we can use a variable wherever we

use a value and JavaScript will

substitute whatever is inside the

variable into the

code let's do another example we're

going to type some new lines and create

a new variable again using

let and we're going to name this

variable

result and we're going to make it equal

to calcul

ation plus 2 and

semicolon so this does the same thing as

a code before it will take whatever

value is inside calculation which is

four and substitute it into this code so

we get 4 + 2 =

6 but this time we have an extra step

we're going to save this result which is

six into another

variable so so if we

console.log

result and

save we can see that six was saved into

the result

variable again we can use a variable

wherever we use a value now in addition

to numbers we can save any type of value

in a variable including

strings for example let's create a new

variable using

let and let's name this

message and we're going to save inside

this variable a string this time so

quote hello quote and

semicolon again we're going to

console.log this variable so

console.log and

message and a semicolon at the end if we

save

it will show us that the string hello is

saved inside this

variable okay now that we learned how

variables work let's learn the syntax

rules for

variables the word let creates a new

variable and then we give the variable a

name so we can name variables almost

anything we want except for a few

restrictions number one we can't use

special words like let as a variable

name

that's because let already has a special

meaning in JavaScript it creates a

variable so let is a reserved word

however we can use let one or let two as

variable names we just can't use

let number two we can't start a variable

name with a number if we start with a

number JavaScript will think this is a

number instead of a variable name

however we can use numbers in the middle

or the

end lastly we can't use most special

characters like these or a space in a

variable name however there are two

special characters we can use dollar and

underscore so those are the rules for

naming

variables and then to save something

inside a variable we just use the equal

sign and then the value we want to save

and that's it after we create a variable

we can start using it in the rest of our

code now there's one last part of the

syntax that we haven't learned which is

the semicolon we've seen semicolons in

many places already in JavaScript a

semicolon means this is the end of an

instruction it's similar to a period in

English in English a period means this

is the end of a

sentence so here this semicolon tells

Java script that this is the end of an

instruction and now after this we can

add another instruction like

console. log Open Bracket and then the

string semicolon and a semicolon at the

end if we

save it will run these two instructions

one after another without any

problems so if we didn't have the

semicolon here and and we save it

wouldn't work because JavaScript thinks

that this entire line is one

instruction so we need semicolons to

separate different instructions in

JavaScript if we

save everything goes back to

normal so JavaScript is a little special

because it has a feature called

semicolon

insertion that means it will try to

insert the last semicolon in a line of

code automat automatically for example

if we removed the last

semicolon and

save this code will work without that

semicolon and that's because JavaScript

inserts the last semicolon

automatically however a lot of companies

still prefer to use semicolons in their

JavaScript code because semicolon

insertion can sometimes put the

semicolon in the wrong place for this

reason we're also going to use sem

colons in this course to help you get

used to JavaScript code with

semicolons next we're going to learn how

to change the value that is saved inside

a variable for example here we save the

number three inside variable one now

we're going to change the value saved

inside variable one to do that we're

going to go to the bottom and create

some new

lines and we're going to type the

variable name again so

variable one and now to change the value

saved inside we're just going to type

the equal sign and then a different

value like five and

semicolon and now if we console.log this

variable

console.log variable 1 and semicolon and

save it will show us that five is now

now saved inside variable

one notice also that if we scroll up to

the top the first console.log still

displays the value three and that's

because at this point in the code

variable one still contained three we

didn't update the variable yet so when

we first saved a value inside this

variable this is called assigning a

value to a

variable then when we change the value

inside this varable iable this is called

reassigning a value to a

variable now let's learn the syntax

rules for reassigning a value notice

that we don't use the word let when

reassigning that's because let creates a

new

variable so if we try to use let again

it would try to create a new variable

named variable one however variable one

already exists and we can't create two

VAR variables with the same name so this

would cause an error instead to reassign

a variable we just type out the variable

name and make it equal to something else

so that's the Syntax for reassigning a

variable now we're going to do one last

example before working on the project

let's go to the end of our code we're

going to type some new

lines and this time we're going to re

reassign variable one again so we can

reassign a variable as many times as we

want so let's type variable 1 and then

equals and we're going to type variable

1 + 1 and

semicolon so we learned earlier that we

can use a variable inside a calculation

and it will substitute whatever value is

inside the variable

here we're also using a variable inside

the calculation but we're using this

variable

itself so it's essentially taking this

variable increasing it by one and then

saving it

back if we

console.log this variable variable

one and

save variable one now contains six so it

took the previous value in variable one

which was five added one and then saved

it

back so this is how we increase the

value of a variable by a certain

number okay now that we know how to

create and reassign variables we're

ready to work on a project so I actually

prepared a project that we can do for

this lesson and we can see this project

by going to our browser clicking at the

top and and typing

super simple

dodev SL projects SLV

variables and press

enter so we're going to work on the cart

quantity feature of the final project so

in the final project we have a number in

the top right corner that shows how many

products are in our cart when we click

the add to cart button this quantity

will increase

so what you see here is a simple version

of the cart quantity feature that we can

create right now let's go over how it

works first make sure you have the

console open on this page now when we

click the show quantity button it will

show us that there are zero products in

our cart if we click the add to cart

button it will increase the quantity by

one and display it in the console

if we click add to cart again it will

increase the quantity by one again now

in the final project we can also add

more than one product at a time using

this

drop-down for now we're going to build a

simpler version of that we're going to

use the plus two and plus three buttons

to add multiple products so when we

click the plus two button it will

increase the quantity by two and display

it in the console

and when we click the plus three button

it will increase the quantity by

three and finally when we click the

reset cart button it will reset the

quantity back to zero and display this

message in the

console so now that we understand how

this project Works let's build this step

by step first let's create a new HTML

file just for this project we're going

to go to our code editor and click this

icon to show our files and then click

this icon to create a new

file let's name this file 05

dcart D

quantity.

HTML and press

enter next let's open variables. HTML

and we're going to copy all the code

here into our new

file let's type control a on Windows or

command a on Mac to select all this code

and then

rightclick

copy and then in our new

file right click and

paste let's close this for

now and in the new file we're going to

change the title to cart quantity

and let's remove all of our JavaScript

code but keep the script element because

we're going to write new JavaScript

code now we're ready to begin let's

start by creating these

buttons let's go to the body element

going to create a new

line and here as we learned in the

previous lesson we can create a button

using this HTML code less than button

greater than and the closing tag less

than SLB button greater

than inside this button we're going to

have the text show

quantity and let's

save now let's open this file in live

server by right clicking and then open

with live

server and we can see that we created

the first button now let's create the

other buttons here feel free to pause

the video if you want to try it

yourself we're going to go back to our

HTML and create another

button inside this one we're going to

have the text add to

cart let's create another

button this one is going to have the

text plus

two and we'll create another

button this one is going to be + 3 and

finally we'll create the last

button and this one is

reset

cart and now let's

save and if we go back to our

tab we've created all the

buttons now let's make this web page

interactive with

JavaScript first of all we need

somewhere to save the cart quantity so

as we learned in this lesson variables

are the perfect solution for this

variables let us save a value so let's

go into the script element and we're

going to create a variable by typing

let and this variable is going to save

the cart quantity so let's just name it

cart capital Q

quantity so the card quantity will start

out at zero so we're going to type equal

Z and

semicolon next when we click the show

quantity button we want to display the

quantity in the console to do this we

learned a special HTML attribute in the

previous lesson called the onclick

attribute so we're going to type in this

opening tag here space

onclick equals and double quotes So the

onclick attribute run some JavaScript

when we click this

button and between the double quotes we

can write JavaScript code so let's press

enter

enter And now when we click this button

we want to display the card quantity in

the console so let's type

console.log Open Bracket close bracket

semicolon and then between the brackets

we're going to display a message

now if we go back to Super

simple. and we click show

quantity we want to display this message

in the

console so in our code between the

brackets we're going to type the string

quote cart

quantity colon

0 now let's save and go back to our tab

to try it

out so we're going to open the console

first by right clicking and then click

inspect and then click the

console and now when we press the show

quantity button it should display that

message in the

console okay so we just made our project

interactive however we obviously don't

want to display zero every time we want

to display the value inside cart

quantity so we need to insert this value

in inside this

string remember from the strings lesson

when we want to insert a value into a

string we're going to use a template

string so let's switch the single quotes

to back

ticks to create a template

string and now instead of zero we're

going to insert a value using Dollar

open curly bracket and close curly

bracket and in between these brackets

we're going to insert this

variable

cart capital Q

quantity remember that JavaScript is

case sensitive so make sure you type the

variable name exactly the

same now let's

save and click show quantity

again and now it displays the value

inside card quantity in the console so

notice that variables also work with

string

interpolation again we can use a

variable wherever we use a value and it

will just substitute whatever value is

saved inside this variable into the

code now let's make the rest of the

buttons

interactive so when we click the add to

cart button we're going to add one to

this cart quantity and display it in the

console so again we're going to type

here and type space

on click equals double quotes and

between the double quotes we're going to

add

JavaScript let's also add some new lines

here to make our code easier to

read okay so in the onclick attribute

we're going to do two things the first

one is increase the card quantity by

one we can do that by reassigning the

card quantity variable

so we're going to type just the variable

name cart

quantity and we're going to make it

equal to

itself plus one and

semicolon next we're going to display

the updated quantity in the console so

let's press

enter and we're going to display this

message again so we can actually just

copy this code so we'll select it and

then right click and

copy and then

here right click and

paste now if we

save and click the add to card

button we'll see that it increased the

quantity by one and displayed the

updated quantity in the console let's

press it again to make sure it

works so it increases it by one again

and then displays it in the console

so that's basically how the cart

quantity feature works in the final

project first we need a variable to save

the quantity and then when we click a

button we're going to update the

quantity so now let's make the rest of

these buttons interactive feel free to

pause the video if you want to try it

yourself for the plus two button we're

going to add the onclick attribute again

onclick equals double quote

and inside we're going to increase the

cart quantity by two so cart quantity

and then we'll just make it equal to

itself plus two and

semicolon and again we're going to

display the updated quantity in the

console so we can create a new line and

just copy this code so select it right

click

copy and here right click and

paste let's save and click plus two a

few times and we can see that it adds

two to the card quantity and displays it

in the

console for the plus three button we'll

do the

same let's type an onclick

attribute click equals double

quotes and here we're going to increase

the card quantity by three three so cart

quantity equals

itself plus 3 and

semicolon and we're going to display

this in the console again so we'll

select this right click copy and here

rightclick and paste let's save again

and try it out to make sure it works so+

three +

three and finally let's do the reset

card

button so we'll add the onclick

attribute again on click equals double

quotes and inside the double quotes

we're going to do something a little

different this time instead of

increasing the cart quantity we'll set

it back to

zero to do this we can just reassign the

cart quantity variable so cart

quantity and just make it equal to Z and

semicolon now if we go back to

superimple

dodev and try out this reset cart

button you'll notice that it displays

two messages the first message is cart

was reset so we're going to display that

message in our code

first

console.log and the string cart was

reset

and the second message is the same

message as the other buttons so we can

just select

this and then right click

copy and then here right click and

paste and now let's save and go back to

our Tab and give this a

try so the cart quantity starts at zero

when we press add to cart increase in es

by one this increases by two this

increases by three and when we click

reset cart it'll display cart was reset

and reset the cart quantity back to

zero and that's it we just created a

simple version of the cart quantity

feature of our final project using

everything that we learned in this

course so

far now we're going to learn some

shortcuts for reassigning

variables so if we look at this line of

code here we're increasing the value of

this variable by two and then saving it

back well there's actually a shortcut

for this and that shortcut is cart

quantity plus equal 2 and

semicolon so this does the same thing as

the line above but it's just shorter the

plus means we're going to add two to

cart quantity

and equals means we're going to save

that result back to card quantity so we

can actually delete this

line and the code will work the same way

if we

save and try it

out it will still add a two and then

save it back in card

quantity let's scroll up and practice by

using this shortcut for card quantity +

one so instead of this line we can type

cart

quantity plus equal 1 and

semicolon so it turns out that in

programming plus equals 1 is so common

that we have an even shorter shortcut

for plus equals 1 and that shortcut is

cart

quantity plus plus and

semicolon so this is the same thing as

plus equal 1

and all three lines do the same

thing so we can remove these

lines and the code will work the same

because it's just a

shortcut if we

save so if we click add to

cart it will add one every

time so those are some shortcuts for

reassigning

variables we also have these shortcuts

for the other operators like minus

equals multiply equals divide equals and

minus minus I'll leave some exercises

for these other shortcuts at the end of

this

lesson next we're going to learn some

best practices for naming variables so

if we scroll

down notice that our variable cart

quantity has two words in it cart and

quantity we learned earlier that we

can't have spaces in a variable name so

if we want to have multiple words we

have to combine them together like this

now you might be wondering why we wrote

it this way with a lowercase c and a

capital

Q This is actually a naming convention

called cam case in cam case we combine

the words together and capitalize every

word except the first

word so for cart quantity we capitalize

quantity but we keep cart lowercase

because it's the first

word cam case is actually the standard

naming convention for JavaScript all of

our variable names should use cam

case now in programming there are other

naming conventions that exist another

one is called Pascal case Pascal case is

the same as camel case except we

capitalize the first word so for cart

quantity Pascal case would be Capital

cart and capital quantity in JavaScript

there is one feature where we use Pascal

case which we'll learn later in this

course for everything else we use camel

case another naming convention is Kebab

case here we keep the words lowercase

and combine them with a dash like cart

Dash

quantity Kebab case doesn't work in

JavaScript because the dash is already a

minus symbol however we use Kebab case

in HTML and CSS and also in our file

names as you can see

here and finally we have snake case

where we keep the words lowercase and

combine them with underscores snake case

is used in other languages but it's not

really used in

JavaScript so those are the common

naming conventions that we use in

programming now one more thing I want to

note is that when we name our variables

try to pick a name that is not too short

or too long for example instead of cart

quantity we could have named this

variable

C but this name is too short it's hard

to understand what c means we could also

use a name like this quantity of

products in the cart but this name is

too long it's hard to read this in the

code so try to have a balance between a

name that is understandable but not too

long like cart

quantity the last thing we're going to

learn in this lesson is there are three

ways to create variables in JavaScript

let's go back to our variables. HTML

file and we're going to learn those

three

ways so the first way is to use let

which we already learned the second way

to create a variable is to use the word

const so at the bottom we can type const

space and then a variable name like

variable 2 and make it equal to

three so const creates a variable just

like let except we can't change its

value later this value stays constant

that's why it's called const if we try

to change its value like variable 2 = 5

and then and we save this and we open

this file in the browser by right

clicking and then open with live

server and then open the console so

rightclick

inspect and then click the

console it will give us an error when we

try to change this variable so this

doesn't work let's remove this line and

Save

so why would we ever use const instead

of let well const makes our code safer

and easier to understand when we create

a variable with const we know for sure

that this variable will always contain

three for let however if we create a

variable it's hard to know what value is

inside this variable because later on we

can change this value in our

code so in order to keep our code safer

it's actually a best practice to use

const by default and only use let when

we know that we need to change the

variable so here it's actually best

practice to use const to create this

calculation variable because we're not

changing it later same thing for the

result

variable and the message

variable now for variable one we have to

use let because we're changing it later

in this code

so that's const it creates a variable

that can't be changed

later finally the Third Way of creating

a variable is to use another word VAR so

at the bottom we can type VAR space and

then a variable name like variable 3 and

make it equal to

three so VAR creates a variable just

like let and this variable can be

changed

later VAR is actually the original way

to create variables in JavaScript VAR

means

variable however VAR has some issues

that we'll learn later in this course

and because of these issues we don't use

VAR in new JavaScript code you might see

VAR in older JavaScript code so it's

still useful to know so those are three

ways to create variables in JavaScript

let constant and VAR we use const by

default and if we have to change a

variable then use

let so one more thing we're going to

learn is that we can use type of with

variables so remember that type of tells

us what type a value is for example if

we

wrote

console.

log type of

three and

save type of will tell us that three is

a

number well we can actually use type of

with a

variable so if we change this to

variable 2 and

save type of will tell us the type of

value inside the variable which is a

number and that's what we see in the

console

now let's check the type of this

variable message so message contains a

string and if we do

console.log type of

message and

save this will tell us that the value

inside the message variable is a string

so we can use type of to check the type

of value that is saved inside a variable

and that's the end of this lesson in

this lesson we learned about variables

which are a way to save values and use

them later we learned how to reassign a

variable we created the cart quantity

feature of the final project we learned

some shortcuts for reassigning a

variable we learned some naming

conventions and best practices for

variable names and we learned learned

three ways to create a variable let

const and

VAR here are some exercises to help you

practice using variables

in this lesson we're going to learn two

more features of JavaScript called

booleans and if statements and we're

going to use these features to build

this rock paper scissors

project let's start by creating a new

HTML file for this lesson we're going to

go to our code editor and click this

icon to show our files and then click

this icon to create a new file we're

going to name this file

06-

booleans

HTML and press

enter let's open variables.

HTML and we're going to copy all this

code into our new file let's select the

code using control a on Windows or

command a on Mac and then

rightclick

copy and in

here rightclick and

paste let's close this for now and

prepare this file for this lesson so

we'll scroll to the top and change this

to

booleans and then remove all the

JavaScript code but keep the script

element

now let's

save and open this file in live server

by right clicking and then open with

live

server and we can close the previous

tabs as well as the previous code for

now we'll start by learning what are

booleans so far in this course we learn

two types of values in JavaScript

numbers and strings booleans are another

type of value in JavaScript but booleans

are special because there are only two

Boolean values true and

false let's click in the script element

and type true press enter and type

false so these are the only two Boolean

values that exist true and false so

what's the purpose of Boolean values a

Boolean value represents whether

something is true or

false for example in JavaScript we can

compare two numbers let's create some

new lines and type the code 3 less than

5 so this code checks whether the number

three is less than five and of course

this is true so if we console.log this

code console.log

and

save and then go to our website and open

the console rightclick

inspect and

console it will show us that the result

of this code is the Boolean value

true let's try another

example let's delete this less than

symbol and replace it with a greater

than symbol so now this code checks

whether three is greater than five

and we know that three is not greater

than five so if we

save the computer will tell us that the

result of this comparison is the Boolean

value false so as you can see a Boolean

value represents whether something is

true or

false now let's learn the syntax rules

for booleans to create a Boolean we just

type true or false note that we don't

surround these with quotes like this if

we surround them with quotes this is now

a string not a

Boolean we can use type of to check this

so at the front we can type

console.log type of

true if we

save this will tell us that this is a

string now if we remove the

quotes and Save

this will tell us that this is now a

Boolean so when creating a Boolean don't

put quotes around true or

false let's

save now one way to create a Boolean is

to compare two numbers for example 3

greater than 5 so this greater than

symbol is called a comparison operator

and there are many other comparison

operators we can use

we saw less than earlier and we also

have greater than or equal to less than

or equal to Triple equals which checks

if two values are equal to each other

and exclamation double equals which

checks if two values are not equal to

each other now JavaScript is a little

special because it has two ways to check

if two values are equal triple equals

and double equals the difference is that

double equals tries to convert both

values into the same type for example in

our code let's create some new lines and

console.

log and let's check if the number five

is equal to the string

5. if we

save it will tell us that these two

values are equal to each other even

though one of of them is a number and

the other is a string and that's because

the double equals converts both values

into the same type so converts both of

these into the number five and then

Compares them so that's why they are

equal however this is not a good idea

because this value is a number and this

value is a string it's a piece of text

so they shouldn't really be equal to

each other that's why in JavaScript we

always use the triple equals to check if

two values are the same so that we avoid

the conversion behavior of double equals

so if we

save now it will tell us that these two

values are not equal to each other

because one value is a number and the

other value is a

string so this rule also applies to not

equal to in JavaScript we always use

exclamation double equals instead of

exclamation equals to avoid the

conversion

Behavior All right so those are

comparison operators in the order of

operations comparison operators have a

lower priority than math so if we did

something like 5 and then minus

5 this would calculate 5 - 5 first which

is zero and then compare the two numbers

so three is now greater than zero so if

we

save the first comparison will now be

true so comparison operators have a

lower priority than math

operators now that we know what Boolean

values are we're going to combine them

with a really useful feature called if

statements an if statement lets us write

multiple groups of code and then decide

which code to run Let's do an example

and create our first if statement we're

going to go to the the

bottom and create some new

lines and type if and Open Bracket Clos

bracket and open curly bracket closed

curly

bracket between these round brackets

we're going to put a Boolean value like

true and in between the curly brackets

we're going to put some code to run for

example console.log

hello so the way that an if statement

works is that if this Boolean value is

true then we're going to run the code in

the curly brackets if this Boolean value

is false then we're not going to run the

code if we

save the value between the brackets is

true so we're going to run this code and

display

hello now if we change this to false and

save it will not run this

code so an if statement lets us decide

whether or not to run some code based on

this Boolean

value now if statements have another

useful feature called

else let's go to the end of this if

statement and

type

else open curly bracket close curly

bracket and then inside these curly

brackets we're going to put some

different code like

console.log

else the way else works is if this

Boolean value is true the computer will

run this code otherwise we will run the

code inside

else let's give it a try we'll change

this Boolean value to true and

save and because it is true it will run

this code

and display

hello now if this Boolean value is false

and

save because it is false it will not run

this code and it will run the code

inside else and display

else so using IF and else we can write

two groups of code and then decide which

code to

run now let's do a practical example

we're going to write some code to check

if someone is old enough to

drive let's go to the bottom and create

some new

lines and we're going to type if

brackets and curly

brackets and inside here we're going to

compare two numbers the first number is

a person's age let's pretend we have a

person who is 30 years old so we're

going to type

30 then we're going to check if this age

is greater than or equal to the legal

driving age Let's Pretend the legal

driving age is

16 notice that between the brackets we

don't have to just put a Boolean value

we can put any code that results in a

Boolean

value so this comparison results in the

Boolean value true that means the

computer will run the code between the

curly brackets so in here let's type

console

.

log you can

drive now if this is not true let's run

some different code at the bottom we'll

type

else and curly brackets and then inside

these brackets we'll type

console.log you canot drive

now let's

save and it will tell me that this

person who is 30 years old can

drive if we go back and change this to a

person that is 15 years old and

save this comparison will result in

false so it will display you cannot

drive so that's how we use if statements

we can write multiple groups of code for

different situations and then decide

which Cod code to

run now let's learn the syntax rules for

if statements to create an if statement

we type if and then round brackets with

a Boolean value inside this is called

the condition if this condition is true

we will run the code inside the curly

brackets we can also add an else

statement this code will run if the

condition is false the else statement is

optional we don't have to have

one so these curly brackets and the code

inside these are called branches because

it's like a tree branch the code is

splitting off into two directions and we

either run this code or we run this

code one more thing to know is in a

branch if we only have one line of code

the curly brackets are actually optional

so we can delete these and the code will

still work

however if we have more than one line of

code in this Branch for example if we

add another line

console.log

congrats now this branch has two lines

of code so the curly brackets are

mandatory so we have to add them

back now we're going to learn another

feature of if statements which is we can

have more than one condition for example

we're going to go to the end of this if

branch and type else if and then

brackets and curly

brackets else if lets us add another

Branch to our if

statement between these round brackets

we can add another condition for example

if a person is almost old enough to

drive let's display a different message

so inside this condition

let's check if this person's age which

is 15 is greater than or equal to 14 so

we're checking if they are almost old

enough to drive and now inside the curly

brackets we're going to display a

different

message

console.log almost

there so the way this works is that the

if statement checks the condition one by

one first it checks if this is true if

it is it will run this Branch then it

checks if this is true if it is it will

run this branch and if none of the

conditions are true it will run the else

Branch so here this condition is false

so we're not going to run this code but

now the second condition is true so

we're going to run this code if we

save we display almost there

in the

console so using else if branches we can

add as many conditions as we want to an

if

statement the next thing we're going to

learn is that we can combine if

statements with variables from the

previous

lesson for example here we wrote the

person's age two times so we can

actually save this age in a variable and

then reuse that

value so above the if statement

let's create a variable using const and

let's name this variable H and we'll

make it equal to

15 remember the best practice for

creating a variable is to use const by

default and only use let if we're going

to change this value

later and now that we saved this number

in a variable we can use the variable

inside the if statement so we'll replace

15 with age and here as well with

age so this will take whatever value is

inside the variable and substitute it

into the

code if we

save the if statement works the same way

as before and we run this

line okay now we're ready to use

booleans and if statements to do a

project we're going to build a rock

paper scissors gate G first let's take a

look at the project we're going to go to

our browser and at the top create a new

tab and we're going to type here

superimple dodev SL

projects SL

booleans and press

enter here we can see a simple version

of a rock paper scissors game and if we

click this link it will take us to the

final version of this game so in this

game we can pick a

move and then the computer will pick a

random move and it will show us the

result and we also have a score of how

many times we won lost and tied so we're

going to build this as we go through the

course but for now let's go

back and we're going to start by

building this simple version of the game

so how this simple version works is we

click one of these buttons to pick a

move so let's pick

Rock then the computer will randomly

pick a move in this case it's paper but

for you it might be different and it

will compare the two moves and display

the results in this

popup so the rules of rock paper

scissors are rock beats scissors paper

beats Rock and scissors beats

paper let's press okay and we'll get

started on this

project first we'll create a new HTML

file just for this project let's go to

our code editor and click here and

create a new file and we're going to

name this file

06-

rock-paper-scissors HTML and press

enter next let's copy all the code from

booleans HTML into this new file so

we'll open this again and then control a

or command a to select all the code and

then right click

copy and in here right click and

paste let's close this and prepare this

file so we'll change this to rock

paper

scissors and remove all of the

JavaScript code that we had

before finally let's save and open this

file in the browser by right clicking

and then open with live

server let's take a look at the project

again so we're going to start by

creating the text first because this

text is in the final version of the

project so in our

HTML we're going to create a paragraph

element for this text so less than P

greater than and the closing tag less

than /p greater than inside our

paragraph we're going to have the text

rock paper

scissors next let's create the

buttons so we'll go to our

HTML and create a

button and inside this first button

we'll have the text

Rock Let's create another

button this one will be

paper and we'll create the last

button this one will be

scissors now let's save and check our

new

tab and now we created all the elements

that we

need next let's make these elements

interactive with Javas JavaScript so

when writing JavaScript a good strategy

is to think about what steps we need to

do and then convert those steps into

code so here when we click a button the

first step is the computer will randomly

select a move and then we're going to

compare the moves to get the result and

finally we'll display the result in a

popup by the way this is called an

algorithm an algorithm is a set of steps

to complete delete a task or to solve a

problem now that we know what steps we

need to do we're going to convert these

steps or this algorithm into

code first we're going to run some

JavaScript when we click these buttons

so let's use the onclick attribute again

we'll go to the opening tag of the

button and type

onclick equals double

quotes and then inside these double

quotes we can add our JavaScript

so now we have to figure out how to

randomly select a move for the computer

to do this we need to learn a new piece

of JavaScript

code so here we're going to type capital

m

math.random Open Bracket close bracket

math.random generates a random number

between 0o and 1 so if we console.log

this console

log and

save and click this

button and then check in our console by

right-clicking

inspect and the

console it will display a random number

between Z and 1 if we click this button

again it will generate a different

random number so every time we run MTH

random it generates a different random

number between 0 and one now to be more

precise it actually generates a number

greater than equal to zero and less than

one now let's save this random number in

a variable so we can use it later so

we'll replace the

console.log with

const and then a variable name let's

just name it random capital N number

and then

equals so we saved this random number

inside this

variable next we need a way to convert

this random number into a move like rock

paper or scissors to do this let's

imagine the space between 0 and 1 and

then divide the space into three equal

parts each part represents a move if we

generate a random number and it's

between 0 and 1/3 the move will be Rock

if it's between 1/3 and 2/3 the move

will be paper and if it's between 2/3

and one the move will be scissors this

is how we can convert the random number

into a move and this will give the

computer an equal chance of picking rock

paper or

scissors now let's convert these steps

into code and an if statement is the

perfect solution for this this already

looks like an if statement so in our

onclick attribute let's add some new

lines and type if brackets and curly

brackets for this first condition we're

going to check if the random number is

between 0 and 1/3 so let's check if

random number is greater than or equal

to

zero but in this case we also need to

check that random number is less than

1/3 because we're checking if the number

is between 0 and 1/3 but how do we do

this how do we check that two

comparisons are both true to do this

we're going to learn another type of

operator in JavaScript called logical

operators logical operators let us

combine Boolean values which is what we

need to do here let's go back into

booleans

HTML and we're going to learn logical

operators so first let's open the tab

for this

file and we're going to comment out all

the previous code so our console doesn't

get too messy

slashstar and then at the

bottom star

slash now let's create some new

lines and the first logical operator

we're going to learn is called the and

operator

let's type

console. log a Boolean value

true and another Boolean value

true so this is the and operator and it

checks if two Boolean values are both

true so it checks if the left side is

true and the right side is true that's

why it's called the and operator so here

the left side is true and the right side

is also true so the and operator will

result in true if we

save this displays true now if one of

these sides is false for example if we

change this to

false now let's check is the left side

and the right side both true in this

case no so and will now result in false

if we save it now displays false

so that's the logical and operator it

checks if the left side is true and the

right side is also true so this is

exactly what we need for our project for

example let's create a new line and type

console.log and let's say that we

generated a random number like

0.2 and we want to check if it's between

0 and 1/3 so we can do

0.2 is greater than or equal to 0 and

we're also going to check if

0.2 is less than

1/3 so we're using the logical and

operator to check if the left side is

true and the right side is also true so

in this example both sides are true 0.2

is between 0 and 1/3 so if we save

this whole thing will display true now

in the order of operations logical

operators like and have a lower priority

than math and comparisons so in this

example it will calculate the math first

and then it will calculate the

comparison on the left and then the

comparison on the right and then at the

end the and operator checks if both

sides result in

true now let's use the and operator in

our project let's go back to the file

for our

project and then inside this first

condition we're going to check if the

random number is greater than or equal

to zero and at the same time is the

random number less than 1/3 so this is

how we check if a number is between 0

and

1/3 in this case the computer will pick

Rock so between the curly brackets let's

just type con

cons. log

Rock let's get some practice and create

the other two branches for picking paper

and scissors feel free to pause this

video if you want to try it yourself

first so here we're going to type else

if to add another branch and then

brackets and curly brackets and in this

condition we're going to check if random

number is greater than or equal to

1/3

and

random number is less than

2/3 so if this random number is between

1/3 and 2/3 inside here we're going to

console do log

paper and finally let's create another

Branch using else

if random

number greater than or equal to

2/3 and random number less than

1 and

console.log

scissors if we

save and then go back to our rock paper

scissors tab

and then click the rock button a few

times it will pick some random moves for

the

computer so that's how we generate the

computer's move one thing I want to

point out is that I use the less than

comparison instead of less than or equal

to I just did this so that the

comparisons don't

overlap before we continue in the

project we're going to learn two other

logical operators we can use let's go

back to booleans

HTML and let's also open the tab for

this

file the next logical operator is called

the or operator for example let's type

some new lines and type

console.log true or

false so this is the logical or operator

it checks if at least one side is true

so it checks if the left side is true or

the right side is true that's why it's

called the or

operator so here one of these sides is

true so the or operator will result in

true if we

save this displays

true if both sides are true it will also

result in true because at least one side

is

true the last logical operator we're

going to learn is called the not

operator for example let's create a new

line and type

console. log exclamation

true so the exclamation is called the

not operator the not operator only uses

one Boolean value and it flips it into

the opposite value so if this value is

true the not operator will flip it into

false so if we

save this will result in false now if

you think about it if we say that

something is not true that's the same

thing as saying that it is false so

that's why this is called the not

operator now if we change the value to

false again the not operator will flip

this into true so if we

save this will now result in true

so those are the logical or and not

operators we don't need to use these in

our project right now but I'll leave

some exercises for these at the end of

this lesson now let's go back and

continue the project let's open the code

and open the

tab the next step is to compare the

computer's move to our move which is

Rock so first let's save the computer's

move in a variable so we can compare it

later so instead of

console.log we're going to create a

variable with

const

computer capital M move and make it

equal to the string

Rock and we'll do the same thing

here const computer move equals

paper and

here const comp futter move equals

scissors and now at the bottom let's

console.log the computer move variable

to make sure that it

worked if we save and then click our

Rock

button unfortunately it gives us an

error telling us that computer move is

not defined even though we created it

right here so what is happening here if

statements have a special feature they

create something called a scope a scope

limits where a variable exists basically

whenever we have these curly brackets

like this any variable we create inside

the curly brackets will only exist

inside the curly brackets and we can't

use these variables outside the curly

brackets so this is called a scope

Scopes are a feature of many programming

languages and they help us avoid naming

conflicts for example if I create a

variable here called random number

equals

0.5 and this didn't create a scope so if

I delete these curly

brackets this variable name will now

conflict with the variable name up here

because we can't have two variables with

the same name so you can imagine that if

we didn't have scope and we had hundreds

or even thousands of lines of code we

would quickly start to run out of

variable names so by creating a new

scope here all the variable names inside

the scope only exist between the curly

brackets and it won't affect anything

outside in the code so Scopes help us

avoid naming

conflicts okay so I'll delete this

example and we'll learn how to access

this variable

outside of this scope so to access this

variable outside of the if statement we

have to create this variable outside of

the if statement so above

here we can create this

variable

const

computer move and let's just make it

equal to the empty string for

now so this variable was not created

inside any curly brackets so it's

accessible from all of this code inside

the onclick attribute including inside

the if

statement and then inside the if

statement instead of creating a new

variable we're just going to save the

move inside this variable up here

because we can access this variable

anywhere else in the

code so instead of using const we're

just going to reassign computer move and

we're going to move it here as well and

here as

well and remember when we reassign a

variable we have to switch from const to

let and now if we

save and then click the rock

button we're able to console.log

computer move because computer move is

no longer inside this scope it's up here

so we can access it in this line of code

so that's how scope Works any variable

that we create inside the curly brackets

will only exist inside the curly

brackets so remember in the previous

lesson we learned a third way of

creating variables called VAR the issue

with VAR is that it doesn't really

follow the rules of scope for example

here if we create a variable with VAR

like VAR and

random number

equals

0.5 this variable will conflict with the

variable up here with the same name even

though it's inside a scope so that's why

we don't use VAR anymore and we just use

const and let because of VAR doesn't

really follow the rules of scope so we

can remove this for now and move on to

the next

step so we generated a random move for

the computer

now we have to compare our move which is

Rock to the computer's move to get the

result and see who wins to do that we'll

use another if statement so at the

bottom here let's type if and then

brackets and curly

brackets and then inside this condition

let's check if the

computer move is equal to rock

so remember in JavaScript we always use

triple equals instead of double equals

to avoid the conversion

behavior and now if the computer's move

is rock and our move is Rock then inside

the curly brackets the result is going

to be a

tie and let's save the string in a

variable so we can use it later again we

have the same situation as before we

don't want to create the variable inside

here because then it only exists in this

scope between the curly brackets instead

we're going to create the variable above

outside the if statement so we'll use

let to create this variable because

we're going to reassign it in the if

statement let's name this variable

result and just make it equal to the

empty string at the top and then in the

if statement we'll save the result into

this variable

so

result equals

tie now let's create the other branches

of this if statement so here we'll add

else if brackets and curly

brackets and we'll check if the

computer move is equal to paper this

time if the computer move is paper and

we picked Rock

then we lose so the result is equal to

you

lose and finally we'll add another else

if brackets and curly brackets and we'll

check if the

computer move is equal to

scissors and if the computer picked

scissors and we pick Rock the result is

is that you

win so that's how we compare our move to

the computer's random move using an if

statement the last step is to display

this result in the

popup so at the bottom let's create a

popup using alert Open Bracket close

bracket and let's go back to super

simple Dev to see the message in the

popup so we'll click this and in the

popup it shows our move the computer's

move and then the result so we can

actually just copy

this rightclick

copy and then in here right click and

paste so obviously the computer is not

going to pick this move every time and

this is not going to be the same result

every time instead we want to insert

computer move into here and we want to

insert result into here so because we

want to insert values we're going to

turn this into a template string using

back

ticks and now instead of paper we're

going to insert a value using dollar and

curly brackets and we're going to insert

the variable

computer

move and instead of this text every time

we're going to

insert the variable

result and now if we

save and we can click okay to close this

and go back to our Tab and click the

rock

button we're going to pick Rock the

computer will pick a random move and it

will show us the result in a

popup so that's how we create this

simple version of rock paper scissors in

our code we did things step by step

first we generated a random number we

converted it into a move for the

computer and then we compared our move

to the computer move and we displayed

the result in a

popup so as you can see when we're

writing JavaScript we first figure out

what steps we need to do this is called

an algorithm and then we convert these

steps or this algorithm into

code so now now we can actually remove

this console.log because we don't need

it

anymore and the last step is to make the

other buttons here interactive so feel

free to pause this video if you want to

try it yourself

first for the paper button let's add

some new lines to make it a little

easier to read and again we'll add the

onclick

attribute and then inside here we can

actually make a copy of all the

JavaScript we wrote so we can select all

of

this and then write click

copy and then in here right click and

paste if the formatting doesn't look

right we can select all of these

lines and press tab to add indents until

the formatting looks good

the one thing we have to change here is

that now we picked paper so the result

is going to be different if the computer

picks Rock and we pick paper that means

you

win if the computer picks paper now it

means that we tie and if the computer

picks scissors that means you

lose and here what will also change up

pick Rock to

paper and that's

it the last step is to make the scissors

button interactive so again

onclick equals double

quotes and then we'll make a copy of the

code so I already have it so just write

click and

paste and then again select the code

that we need to fix the formatting for

and press

Tab and here we pick scissors so if the

computer picks Rock then the result is

you lose if the computer picks paper the

result is you win and if the computer

also picks scissors the result is a

tie and we'll change you pick Rock to

scissors

now if we save and try out our game if

we click Rock we're going to pick Rock

computer picks a random move and it will

show us the result here let's press okay

and try

paper this also works correctly let's

press

okay and click

scissors and this also works

correctly and that's it we just finished

creating a simple version of this rock

rock paper scissors

game in the rest of this lesson we're

going to learn more details about

booleans and if

statements let's go back to booleans

HTML and open the tab for this

file and let's comment out the previous

code using

slashstar and star slash and create some

new

lines the next thing we're going to

learn is called truthy and and falsy

values so if statements don't just work

with Boolean values like true and false

they actually work with any type of

value including numbers and strings for

example let's type if brackets and curly

brackets and inside this condition

instead of putting a Boolean value we're

going to put a number like five and then

in inside the curly brackets let's

console.log the string

truthy if we

save the number five behaves just like

true it causes the if statement to run

this code so we call this value a truthy

value because it behaves just like true

now let's change this value to a

different number zero if we say

the number zero behaves just like false

it causes the if statement to not run

this code we call this value zero a

falsy value because it behaves just like

false so how do we know if a value is

truthy or falsy in JavaScript the list

of falsy values are false the number

zero the empty string Nan undefined and

null

any value that is not on this list is a

truthy

value so why do we use truthy and falsy

values one way we use them is like a

shortcut in our code for example let's

create a variable at the bottom using

const and let's call it cart

quantity and make it equal to

five next let's create an if statement

if brackets and curly brackets and

inside the curly brackets let's type

console.log the string cart has

products now let's say that we only want

to display this message if our cart has

products usually inside this condition

we would check if cart quantity

is greater than zero but now instead of

doing this comparison we can actually

just type cart quantity and it will

behave the same way if the card quantity

is not zero they will both behave like

true if the card quantity is zero they

will both behave like false so here the

card quantity is five which is a truthy

value if we

save this caus the if statement to run

this code as you can see instead of

doing comparisons we can use truthy and

falsey values as

shortcuts truthy and falsy values also

work with logical operators for example

if we

console.log the not operator and the

number

zero zero is a falsy value it behaves

just like false so the not operator will

flip it into true if we

save this will display

true now that we understand truthy and

falsy values let's go over the list of

falsy values because there are some that

we haven't learned yet we already

learned false zero and the empty string

the next falsy value is Nan which means

not a

number we get Nan if we do some invalid

math for example at the bottom let's

type

console.log the string

text divided by the number

five so obviously this is not valid math

if we save JavaScript will tell us that

the result of this calculation is not a

number or

Nan the next falsy value is undefined

undefined represents that something

doesn't have a value for example at the

bottom if we create a variable with

let variable one and we don't give it a

value and then we

console. log this

variable and we

save it will show us that variable one

contains the value undefined so

undefined represents that this variable

doesn't have a

value one thing to note with undefined

is that we can only use this syntax with

let we can't use it with

const if we really want to use this with

const we have to type out equals

undefined

directly the last faly value is null

we'll need some extra knowledge to

understand null so we'll learn about

null later in in this

course the last thing we're going to

learn in this lesson are some shortcuts

for if statements called the Turner

operator the guard operator and the

default

operator first let's comment out this

code so our console doesn't get too

messy SL star and then at the bottom

star

slash and let's scroll down and we'll

start by learning the Turner operator

we're going to type a Boolean value like

true and question mark another value for

example the string

truthy and then colon and another value

like the string

falsy so this is the Turner operator

this is similar to an if else statement

the first value is like the condition if

it's truthy the result of this code is a

value after the question mark if the

first value is falsy the result of this

code is the value after the colon so you

can think of the question mark as the if

branch and the colon as the else Branch

this is sort of like a shortcut for an

if statement like

this now an advantage of the Turner

operator over an if statement is that we

can save a tary operator in a variable

so at the front

we can do

const result

equals and now if we

console.log the

result and

save the first value is true so the

value after the question mark gets saved

in the

variable as always we can use truthy and

falsy values instead of just true and

false so here if we change the first

value to a falsy value like zero this

will cause the value after the colon to

get saved inside the variable if we

save that's exactly what happens so this

is the turnery operator it's sort of a

shortcut for an if else statement like

this the next shortcut is called the

guard operator earlier in this lesson we

learned the and operator which checks if

two sides are both

truthy the and operator has a special

feature let's say we have an and

operator and the left side is

false in this situation we already know

it's impossible for both sides to be

truthy so we don't even need to check

the right side so the and operator

actually stops early and doesn't even

run the code on the right this is called

a shortcircuit

evaluation for example let's go into our

code and create some new lines and we'll

type

false

and

console.

log

hello if we

save the left side is falsy so the and

operator stops early or short circuits

and it doesn't even run the code on the

right so as you can see we can use the

value on the left to block or guard the

code on the right so when we use the and

operator like this we call it the guard

operator this is sort of like a shortcut

for an if statement like

this and just like the Turner operator

we can save the guard operator in a

variable for example let's create a

variable const

message and make it equal to

false and the string

hello if the first value is falsy the

guard operator will stop early and the

result will be the first value if we

console. log this

message and

save the value f false will be saved

inside this

variable now let's change this value to

a truthy value like the number five now

it will not stop early and it will give

us the second value as the result if we

save the string hello is now saved

inside this

variable this is sort of like a shortcut

for an if statement like this so don't

worry if it's a bit confusing all of

these are just shortcuts for an if

statement they're sort of like an if

statement that we can write on a single

line the last shortcut is called the

default operator which is similar to the

guard operator but uses

or earlier in this lesson we learned the

or operator which checks if at least one

side is truthy let's imagine we have an

or operator and the left side is

true in this situation we already know

the result of the or operator because

the left side is already truthy we don't

even need to check the right side so the

or operator also stops early or short

circuits if the first value is truthy

for example let's create some new lines

and let's say that in our final Amazon

Project we can choose a currency to pay

for our order let's create a variable

with

const currency and make it equal to the

string e or

Euros now let's say that choosing a

currency is optional if we don't choose

a currency we'll use a default value of

USD or United States dollars to create a

default value we can go to the end and

type or the string

USD so here

the left side is truthy so the or

operator will stop early and it will

result in the value on the

left if we

console. log the

currency and

save it will display

Euros now let's say that we didn't

choose a currency because it's optional

so let's go here and we're going to

change this currency to

undefined now the left side is falsy so

the or operator does not short circuit

it will continue and the result will be

the value on the right if we

save now the string USD is saved inside

currency as you can see we can use the

or operator to set a default value so

when we use the or operator like this we

call it the default operator

the default operator is sort of a

shortcut for an if statement like

this so don't worry remember that

everything that we learned in this last

section are basically some shortcuts for

if statements we don't have to use them

but they can save us some

typing and that's the end of this lesson

in this lesson we learned about booleans

and if statements Boolean values

represent whether something is true or

false we learned how to use if

statements to make decisions in our code

we learn how to use comparison and

logical operators we learned about

algorithms and created a simple version

of rock paper scissors we learned about

truthy and falsey values and we learned

some shortcuts for if statements the

turnery operator the guard operator and

the default operator here are some

exercises to help you practice booleans

and if

statements in this lesson we're going to

learn the next feature of JavaScript

called functions and we're going to use

functions to improve our rock paper

scissors project first let's create a

new file for this lesson we'll go to our

code

editor and create a new

file and let's name this file

07-

functions.

HTML and press enter

next let's copy booleans HTML to

functions. HTML so we'll click this file

and then select all this code using

control a or command

a and then right click

copy and in

here rightclick and

paste and we'll hide our files and

prepare this file for this lesson

so at the top we'll change the title to

functions and we'll remove all the code

in the script

element and let's

save and we'll open this file in live

server by

right-clicking open with live

server and we're going to open the

console as well so right

click inspect

and then click the

console and finally we can close the

previous

tabs as well as the previous

code okay now we're ready to learn

functions first of all what is a

function a function lets us reuse code

let's create our first function we're

going to go to the script element

and type the word

function and

space so this creates a new function and

then we're going to give a name to our

function we can name it almost anything

we want but for now let's just name it

function one and then we're going to

type round brackets and curly

brackets then inside these curly

brackets we're going to create a new

line

and we're going to type some code so

console.log the string

hello and we'll also type

console.log 2 +

2 and

save so this creates a function now

let's learn how to use this function

we're going to type at the bottom

the function name so

function one and then Open Bracket close

bracket and

semicolon when we type the function name

with brackets this will run the code

inside the function if we

save notice that it runs the code inside

the function and displays the two lines

in the

console so why do we use functions a

function lets us reuse code so if we

wanted to run both these lines of code

again all we have to do is type the

function name again with brackets so

function one and brackets again if we

save this will run the code inside the

function two times and we can reuse this

code as many times as we want by typing

the function name with brackets so

that's what a function is it lets us

reuse code now let's learn the syntax

rules for functions the word function

creates a new

function and then we choose a name for

our function the rules for function

names are the same as variable names we

can't use special words like function we

can't start with a number and we can't

use special characters although dollar

sign and underscore are allowed and just

like variable names the best practice is

to use camo case for function

names and inside these curly brackets we

put the code that we want to run when we

use the function this is called the

function body now one very important

thing to remember is that this code only

creates a function it doesn't run the

code in the function or do anything else

in order to actually run the code we

have to use the function like below by

typing the function name with

brackets this is known as calling the

function it's also known as running the

function or executing the

function now that we learned the syntax

rules for functions let's do a practical

example we're going to use functions to

improve the code of our rock paper

scissors project first let's click here

to show our files and we're actually

going to make a copy of the project just

for this lesson so we're going to

rightclick this

file

copy and then at the bottom right click

and

paste and we're going to rename this

file so rightclick

rename remove copy at the end and then

at the beginning we'll change this to

07 and press enter

next we're going to open this file in

live server by right clicking and then

open with live

server and let's also open the console

on this page we'll right click

inspect and then click the

console all right now if we look at the

code for generating a computer move

you'll notice that this code is the same

for all three

buttons so this is a perfect situation

to use a function because a function

lets us reuse code so let's scroll down

to the script element and we're going to

make a function here so let's type

function and then a function name let's

name this function

pick

computer move and then brackets and

curly brackets so one recommendation for

function names is to use a verb or an

action in the name such as

pick so next we're going to move all the

code for picking a computer move into

our new function so let's create a new

line here and we'll scroll up to the

scissors button because it's the closest

one and we'll select all of this code

for picking a computer move and then

rightclick

cut and inside the

function right click and

paste if we need to fix the formatting

we can select these lines and press tab

to add

indents so the reason we created this

function in the script element is

because remember that the script element

runs when the page is loaded so we want

to make sure that we create the function

first and then we use it in the buttons

after now remember this code just

creates a function it doesn't actually

run the code inside to run the code

inside we're going to call this function

so let's scroll up to the scissors

button and we're going to call this

function by typing the function name

pick computer move Open Bracket close

bracket ET and

semicolon if we

save and then click the scissors

button unfortunately it now gives us an

error saying computer move is not

defined now this might seem weird

because down here we actually create the

computer move so what's going on the

reason this happens is because functions

create a scope in the previous lesson we

learned about Scopes which limit weight

where a variable exists we learned about

if statements and that if statements

create a scope between the curly

brackets this means that any variable

created between the curly brackets only

exist between the curly

brackets functions also create a scope

any variable that is created between

these curly brackets only exists inside

the curly brackets and we can't use it

outside the curly Brack ETS like we do

here so that's why we're getting this

error so how do we solve this problem

remember that with if statements we

solve this by creating the variable

outside of the if statement like this we

can use a similar solution with

functions to make this variable exist

outside the function we just have to

create it outside the function so let's

select this code we're going to

rightclick

and

cut and remove these lines and then

outside the function we're going to

rightclick and

paste so now this variable is no longer

inside the function's scope and it can

be used anywhere else in the code so

variables like this that can be accessed

anywhere are called Global

variables if we save

and now click the scissors

button everything is working again

because this code above can now access

this

variable now let's press

okay and let's use this function to

reuse this code so we'll scroll up to

the paper

button and now instead of all this code

again we're just going to remove it and

call the function pick

computer move Open Bracket close bracket

semicolon and also with the rock button

we'll select all this

code and remove it and just call the

function

pick

computer move brackets and

semicolon now if we

save and click the rock

button it works just like before

we'll press okay and click the paper

button it also works just like before so

as you can see functions let us reuse

code and they make our code a lot

cleaner by removing all the duplication

that we had another benefit of removing

duplication is that before if we ever

wanted to update the code for picking a

computer move we had to update it in

three places in each of the buttons but

now if we scroll

down we only have to update it in one

place inside this function so functions

also make our code easier to update in

the

future next we're going to learn a

feature of functions called a return

statement a return statement lets us get

a value out of a function so at the end

of this function let's type some new

lines and we're going to type type

return and then a value like the number

five and

semicolon now whenever we call this

function it will result in a value the

number five so up

here when we call this function this

will result in the number five so we can

actually console.log this console.log

and then

save and click the scissors

button and it will show us that calling

the function now results in the number

five and we display it in the

console so that's how a return statement

works it lets us get a value out of this

function let's press okay and do another

example we'll scroll

down and this time let's change CH this

value to the string

Rock now whenever we call this function

it will result in the string Rock if we

save and then click

scissors and scroll up

here calling this function now results

in the string Rock and then we display

it in the

console so now let's press okay and

we'll learn the syntax rules for a

return

statement so we just have to type the

word return and then a value and it will

get this value out of the function now

instead of just a value we can also

return a calculation or a variable or

anything that results in a

value so this is known as returning a

value from a function and this value is

known as the return value we also Al

don't have to return anything from a

function if a function doesn't have a

return statement or we return without a

value like this this will return the

value

undefined so if we

save and then click scissors

again the function will return

undefined and lastly when we use a

return statement it ends the function

immediately so after the the return

statement if we type

console.log the string

after and press okay here and save this

file and then click the scissors

button notice that it doesn't run this

code and that's because once we return

the code returns back to where we called

the function that's why it's called a

return statement so it's not going to

run anything after the return so we can

remove this

code and press

okay so now that we understand return

statements we're going to learn a better

way of getting the computer move out of

this function so first let's actually

move this variable back into the

function so we right click and

cut and then in

here right right click and

paste and delete these

lines so now we're back to the original

problem how do we access computer move

outside of the function so another

solution is to return this variable

because remember a return statement lets

us get a value out of the function so

down

here we're going to return the

computer

move so this will take whatever value is

saved inside computer move which is one

of these values and return it out of the

function if we

save and then click these scissors

button we were able to get the move

scissors outside of this function so

what happened here is that we return

this move and then up

here we took the move and displayed it

in the console to get

scissors so that's another way of

getting the computer move out of a

function using the return

statement however now we're back to this

problem with computer move not being

defined because we moved it back into

the function's scope so let's scroll up

and remember that this return value is

just a value we can use it like any

other value for example we can

console.log it or we can also save this

in a variable so let's do that right now

we're going to remove

this and create a new variable with

const and let's just name this variable

computer move to match what we use down

here and we use equals to save the

return value inside inside this

variable so note that even though we use

computer move here as well as here

there're different variables this one is

inside the function's scope so it

prevents it from conflicting with

variables outside the function's scope

that's one of the main benefits of

Scopes so now that we saved the return

value into this variable and we're using

this variable down here the code should

now work work if we

save and click

scissors everything is back to

normal and let's press okay so don't

worry functions can be a little

confusing at first because the code is

no longer simply going from top to

bottom it sort of jumps around a little

bit so let's go through this step by

step when we click this button we're

going to run this function so the code

is going going to jump down here and

then it's going to run all of this code

from top to

bottom at the end we're going to return

whatever is inside computer move back to

where we called this function so we're

going to return all the way back here

and then we're going to save that return

value into a new variable computer move

and then use computer move down

here so following the code line by line

like this is called tracing the code

it's a useful technique to understand

exactly what the code is

doing now let's compare the two

solutions that we used a global variable

and returning a

variable so returning a variable like

this is actually preferred over using a

global variable and that's because a

scope can help us prevent naming

conflicts so all the variables inside

here will not conflict with anything

outside the scope so generally it's a

best practice to keep things inside a

scope if we

can now let's move on and use this

function in the other buttons feel free

to pause the video if you want to try it

yourself

first so we'll scroll up to the paper

button and then here we're going to save

The Returned computer move into a

variable so

const

computer move so that it matches the

code down here make it equal to whatever

is returned and then same thing for the

rock button we're going to save the

return value in a variable const

computer move

equals if we

save and click the rock button

it

works let's press okay and click the

paper button and this also works and

let's press okay so that's how we use a

return statement to take advantage of

the benefits of

scope next if we look at the rest of

this code where we compare our move and

display the result you'll notice that

this code is very similar for each of

the buttons you the only thing that's

different is the result and the message

that we display so we can actually use

functions here as well to reuse code

that has small differences to do this

we're going to need another feature of

functions called

parameters so let's go back into

functions.

HTML and let's open the tab for this

file and let's also comment out the

previous code by typing

slash star and at the bottom star

slash and create some new

lines and now we're ready to learn

parameters so parameters are sort of the

opposite of a return statement a return

statement gets a value out of a function

a parameter puts a value into a function

so let's do an example let's say that

we're working on the final Amazon

Project

and we need to calculate the tax for our

order let's create a function to

calculate the tax so

function let's name it

calculate tax brackets and curly

brackets and then inside the curly

brackets let's say that the cost of our

products is

1,000 or $10 and the tax is

10% to calc calculate the tax we can do

1,000 *

0.1 which is

10% let's also display this number in

the console so at the front we'll type

console.log and

brackets now let's save and remember

this code only creates a function it

doesn't run the code inside to run this

code we're going to call this function

so down here we're going to type the

function name calculate tax and then

brackets if we

save it runs this code and then it

displays the tax which is 100 cents or

$1 however right now this function only

calculates the tax for

1,000 what if we want to calculate the

tax for a different amount how would we

modify this function to work with any

number to do this we're going to learn a

feature of functions called parameters a

parameter lets us put a value into a

function so let's finally create our

first parameter so inside these round

brackets we're going to choose a name

for our parameter so let's just name

this

parameter

1 a parameter one works the same way as

a variable we can save a value inside

this parameter and then use it just like

a

variable so first let's save a value

inside the parameter to do that we're

going to go to where we call the

function and then inside these brackets

we're going to put a value for example

2,000 this will save this value into

this parameter

and now we can use it just like a

variable so instead of

1,000 we're going to type

parameter 1 and it will take whatever

value is inside parameter 1 in this case

2,000 and substitute it into the code if

we

save it now calculates 2,000 *

0.1 to give us 200 cents as the tax

now every time we call the function we

can save a different value into the

parameter for example let's create a new

line and call the function

calculate

tax and this time we're going to save

the value

5,000 into parameter 1 if we

save this line of code will calculate

the tax for 5,000

and result in 500 cents so as you can

see a parameter lets us put values into

a function and this allows our function

to work with any

value now let's learn the syntax rules

for parameters to create a parameter we

just type the parameter name between the

brackets parameter names follow the same

rules as variable names we can't use

special words we can't start with a

number and we can't use special

characters other than dollar sign and

underscore and the best practice is to

use cam

case let's actually change this

parameter name to cost so the code makes

more

sense and

save next when a function has a

parameter we usually say this function

takes a parameter if this parameter

should be a number we say this function

takes a

number when we put a value into the

function like this we call this passing

a value into the function another name

for this value is called the

argument and believe it or not we've

actually used functions and parameters

this whole time the first code that we

learned in this course was alert alert

is actually a function you can tell it's

a function because of the round brackets

and between the brackets we put a string

so this is an example of a

parameter and lastly a parameter only

exists inside the function's scope so we

can only use this parameter between the

curly brackets we can't use it outside

the

function next a function can actually

have more than one parameter for example

right now our calculate TX function can

only calculate a 10% tax but what if

we're in a different country and we want

to calculate a different tax percent to

solve this we can add a second parameter

by typing after the first parameter a

comma and then another parameter name

let's name this tax

percent and now to save a value into the

second parameter we'll go go to where we

call this function and also type a comma

and a second value like

0.2 or a 20% tax so the first value gets

saved in the first parameter and the

second value gets saved in the second

parameter and now we can use our second

parameter just like a variable so

instead of 0.1 every time we're going to

calculate it with tax

percent and it will substitute whatever

value is inside tax percent into the

code if we

save this first line will multiply 2,000

by

0.2 and give us 400 cents as the

result so we can have as many parameters

as we want in a function we just have to

separate them with a

comma Now notice that the second time we

call this function we didn't give a

value for the second parameter if we

don't save a value into the parameter

the parameter will get the value

undefined so here if we

console. log the second parameter tax

percent and

save it will show us that the second

time tax percent is

undefined and then multiplying the cost

time undefined is not valid math so we

get the result Nan or not a number so

now let's remove the

console.log and we'll learn how to fix

this so to fix this we can either pass a

second value into the function like this

line or we can also set a default value

for the parameter to set a default value

we can just type after the parameter

and then add equal sign and a default

value like

0.1 if we

save the second function call Will

multiply 5,000 by the default value

0.1 and give us

500 so that's how we add a default value

for a

parameter all right now that we learned

parameters we're going to go back to the

rock paper scissors project and reuse

even more code so let's go back to the

file for the project and also the tab

for this

project and now if we look at the code

inside each of the buttons you'll notice

that the code is basically the same for

all three buttons the only small

difference is the move that we picked so

this is a perfect situation to use a

parameter so so inside the script

element let's create a new function to

reuse all of this code we'll type

function and let's name this function

play game brackets and curly

brackets next let's move all of this

code inside the function so we can reuse

it we'll select this

code and then

rightclick

cut and inside the

function right click and

paste and if we need to reformat we can

select these lines and press

tab so the value that is different for

each button is the move that we picked

so we're going to turn this move into a

parameter so at the top between the

brackets we're going to create a new

parameter let's name it Player

move and now let's save a value into

this parameter so inside our scissors

button we're going to call this function

and run all this code so let's type play

game and call this function and for the

scissors button let's save the string

scissors into Player move to do that

we'll type between the brackets here and

type the string

scissors so as we learned this will save

scissors into Player move and now we can

use Player move just like a variable in

the

function now let's modify the code based

on the parameter so here this code

calculates the result however this only

works if the player move is scissors so

we're going to put this in an if

statement so we'll type

if

Player move equals

scissors and curly brackets inside this

if statement we're going to put this if

statement so let's select this and then

right click

cut and then inside

here right click click and

paste and select these lines and press

tab so notice that we can put an if

statement inside another if statement

and we did this because this code only

makes sense if the player move is

scissors and finally let's modify the

code that displays the message so here

instead of displaying scissors every

time we're going to display whatever is

saved inside Player

move so we'll replace it with Dollar

open curly bracket close curly bracket

and in between we'll insert Player

move and that's it we modify this

function to use a parameter instead of

always using

scissors now let's save and click the

scissors

button and you'll notice that it works

we displayed the move scissors and we

calculated the result

correctly let's press okay and we're

going to use this function to reuse the

code for the other buttons so we'll

scroll up and for the paper button we're

going to use a different if statement to

calculate the result so let's actually

copy this into the function we're going

to

rightclick click copy

and then inside the

function we're going to create another

Branch if the player move is paper so

here let's type else if brackets and

curly

brackets inside this condition we're

going to check if the

player move is equal to paper this time

and then inside these curly brackets

we're going going to paste the if

statement we copied earlier so right

click and

paste and we can select these lines and

press tab to

reformat so now we have the code that

determines the result for paper down

here we don't need to modify this code

because we're always displaying whatever

is inside Player

move finally we can scroll up to the

paper button

and remove all this duplicated code and

just use our function play

game and we're going to pass paper

inside so now paper will get saved

inside Player move and it's going to run

this if statement

instead if we

save and click the paper

button in this example I pick paper

computer pick Rock and it calculated the

result

correctly let's press okay and use this

function for the rock button feel free

to pause the video if you want to try it

yourself

first so let's scroll up to the Rock

button and first we need to copy this if

statement into the function so let's

rightclick

copy and then inside the function

let's create a branch for rock else if

Player move is equal to

rock and then curly brackets and inside

here we're going to rightclick and paste

the if statement we copied

earlier and now let's select these lines

and press tab a few times to

reformat and again this doesn't need

need to

change the last step is to scroll up to

our Rock button and instead of

duplicating all of this code we're going

to remove it and just call our function

instead play game brackets and then

inside we'll have the string

Rock now let's

save and click the rock

button so I picked Rock the computer

picked paper and we calculated the

result

correctly let's press okay so by using a

function with a parameter we were able

to reuse all of the code in our buttons

and you can see that it made our code a

lot cleaner so lastly notice that inside

a function we can call other functions

let's go through the code step by step

so that we understand how how it works

so here when we call the play game

function we go inside here and then we

call the pick computer move function so

now we're going to go inside this

function and run all the code and then

when this function returns we're going

to return back to where we called it and

then keep going and run the rest of the

code and then when the play game

function finishes it's going to return

back to

here so inside a function we can call

other

functions now one last thing we're going

to do for this code is we'll scroll

down and we're just going to add some

new lines to this if statement to

separate the branches and make the code

a little easier to

read and

save and let's scroll

up and that's the end of this

lesson in this lesson we learned about

functions which let us reuse code we

learned how to get a value out of a

function using return we learn how to

put values into a function using

parameters and we improve the code for

our rock paper scissors project by

reusing the code and removing

duplication

thanks for watching this course so far

if you want to support this channel you

can check out the premium version of my

courses just like this one where you can

get a certificate of completion and a

Better Learning platform if you're

interested in extra videos from me more

in-depth videos and behind the scenes

content you can check out these links

here you can also support the channel by

liking the video subscribing and sharing

this video with others thanks again and

let's go continue with the

course here are some exercises you can

do on your own to practice using

functions

in this lesson we're going to learn

another type of value in JavaScript

called objects and we're going to use

objects to create a score in our rock

paper scissors project first let's

create a new file for this lesson we'll

go to our code editor and click this

icon and then click this icon to create

a new file and we'll name this file

08-

objects.

HTML and press

enter next we'll copy all the code in

functions. HTML to objects. HTML so

we'll type here and press contrl a or

command a to select the code and then

right click

copy and in

here right click

and

paste now let's hide the files for now

and we'll prepare this file for this

lesson so we can change this to objects

and remove all the code in the script

element finally let's save and open this

in live server by right clicking open

with live

server and let's also open the console

on on this page so we'll right click

click

inspect and click the

console let's close our previous

tabs and also the previous

code and now we're ready to learn

objects so what is an object an object

groups multiple values together let's do

an example and create our first object

we'll go to the script element and we'll

create a variable using const and we'll

name this variable product and make it

equal to open curly bracket close curly

bracket and semic it so this is an

object inside this object we can add

some values so we'll type enter and then

Name colon and then a value like the

string

socks and at the end we'll type a

comma and then price colon and another

value like the number

1,90 so inside our object we just added

two values so at the bottom here let's

try console. logging this object

console.log

product and

save and it will display both values

into the

console so as you can see an object lets

us group multiple values together so for

each of these values we have some code

on the left this code is called the

property and using the property we can

access specific values in the object for

example let's type and enter and

console.log we're going to type the

object product and then a DOT and then a

property like

name so dot name Will access the value

that is associated with the name

property which is the string socks so if

we

save it will display the string socks in

the console

let's do another example and we'll

access this second value using the

property price so we'll type enter

console. log the object product and then

a DOT and then a property

price so this will access the value

associated with price which is

1,090 if we save

that's what gets displayed in the

console now we can also use the property

to change a value inside an object to do

that we're going to type the object's

name product and then Dot and a property

like name and just make it equal to

something else like the string cotton

socks so this code will change change

the value associated with the name

property to cotton socks so at the

bottom if we type

console.log the product

again and

save you'll notice the value associated

with the name property was changed to

cotton

socks so that's how an object works we

group multiple values together and then

we can access or change these values

using the properties on the left now

let's learn the syntax rules for objects

to create an object we start with an

open curly bracket and end with a closed

curly bracket inside the object we can

put multiple

values for each value the code on the

left is called the property this is how

we access the value inside the object we

separate the property and value with a

colon and this is called a property

value pair we can have many property

value pairs in an object and we separate

them with a

comma to access a value inside the

object we type the object's name and

then Dot and then the property we want

to access like name this will give us

the value associated with the name

property this syntax is called do

notation if we access a property that

doesn't exist the value will be

undefined to change a value in an object

we can use the dot notation again so

product. name and just make it equal to

something else now using the syntax we

can also add a value to an object we can

type a property that doesn't exist for

example here we can type

product do new

property and make this equal to

something like the Boolean value

true if we

console.log the product

again and

save it will add this value to the

object along with the new

property we can also remove a value from

an object by typing

delete and then the object

product Dot and then the property we

want to delete like new

property if we

console.log the product

again and

save this code will delete new property

from the

object and lastly notice that then an

object is just another type of value we

can save an object inside a variable and

we can also console.log objects if we

check the type of this value so type of

product and

save and scroll up in the

console it will tell us that product is

an object so let's remove

this and Save

and now we'll learn why we use objects

so objects make our code more

organized instead of creating a bunch of

variables for the products values like

the name and the price and other details

we can just group all these related

values together into one object objects

also allow us to use multiple values

together instead of console. logging

each of these values individually we can

just console log the whole object and

display all the values at

once so objects let us group multiple

values together and let us use multiple

values

together next let's do a practical

example with objects we're going to add

a score to our rock paper scissors game

so I've actually prepared a project we

can use for this lesson to see this

project we're going to go to our website

and then create a new

tab and then up here we're going to type

super simple dodev SL projects

slobs and press

enter so this is our simplified rock

paper scissors game again except in this

project when we play the

game it's also going to keep track of a

score so how many times we win lose and

tie and also if we click

okay we have a reset score button so if

we play the game a few

times and add to our

score and then click the reset score

button this will reset the score back to

zero so if we play the game again the

score starts from zero

again so we're going to learn how to use

objects to create create this feature

let's press

okay and first let's create a copy of

our project just for this lesson we'll

go to our code editor and click this

icon to show our files and we'll make a

copy of the rock paper scissors project

from the previous lesson so we'll

rightclick and

copy and down here right click and

paste and we we right click and rename

this

file we'll remove the copy at the end

and at the front we'll change this to 08

and press

enter now let's hide these files and we

can close the 07 file for now and let's

open this in live server by right

clicking and open with live

server let's also open the console on

this page so

rightclick

inspect and the

console all right now let's go into our

code and add a score to our game so

remember when writing JavaScript a good

strategy is to think about what steps we

need to do this is called an algorithm

and then convert those steps into code

so we already had an algorithm for the

rock paper scissors game

let's update this algorithm to include

the score so first the computer randomly

selects a move this step will stay the

same number two we're going to compare

the moves to get the result this step

will also be the same but now we're

going to add an extra step after getting

the result we're going to update a score

and finally we'll display the result and

the score in a popup now let's convert

these updated steps or this algorithm

into code the first thing we need to

change is we added a third step we're

going to save and update a score so

first we need somewhere to save our

score so one place we can save it is

inside a variable let's go to our script

element and at the top we're going to

create a variable for our score using

const

score and make it equal to an

object and inside this object we're

going to have the property

wins so this will keep track of how many

wins that we have we'll type colon and

the number zero because the score starts

at zero and then a comma and then

another property

losses this will be how many losses we

have and then colon and zero and then

another comma and ties colon and zero so

we use an object here because these

values are related to each other you

could use separate variables but we're

using an object for

convenience another thing you'll notice

is that we're creating this variable

outside of a function and outside of a

scope and that's because every time we

make a move we need to update the score

from last time so in order to save the

score from last time we need to keep it

outside the function if the score was

inside the function the function would

create a new score every time which is

not what we want so in this situation in

order to save a score from last time

we're going to keep this variable

outside now every time we play the game

after we calc calate the result we're

going to update the score so let's

scroll down to where we calculate the

result which is here and then below it

we're going to type some new

lines and type the code for updating the

score so we can do that with an if

statement so we'll type if brackets and

curly brackets and inside the condition

we're going to check if the result is a

win if it is a win

we're going to update the winds property

and increase it by one so down

here if the

result is equal to the string you

win and make sure that this string

matches the string up here inside the

curly brackets we're going to update

score. wins and we'll make it equal to

itself plus

one so this is how we increase the winds

property in the score object by one now

remember from the variables lesson that

we have a shortcut for increasing

something by one and that shortcut

is plus =

1 next let's add another Branch to this

if statement for the other two results

so else if brackets and curly brackets

and in the second condition we're going

to check if result is equal to the

string you

lose and make sure this string matches

the string up here so if the result is

you lose we're going to update score do

losses property and increase it by 1 so

plus equal

1 and finally we'll check if the result

is a tie else if brackets and curly

brackets

result equals to the string

tie and here we'll update

score. ties plus equal

1 so we converted this step in the

algorithm to code the score starts at

zero and every time we play the game

after we calculate the result we're

going to update the score using this

code now let's convert the last step

into code we're going to display the

result and the score in the popup at the

end so let's actually go back to the

super simple dodev

project and we'll see what the popup

looks like we'll click one of these

buttons and in this popup on the second

line we display the score so in our

code this is the code that displays that

popup so how do we add a second line to

the popup remember that template strings

have another special feature called

multi-line strings so we can type at the

end of this template string and press

enter to add another line to this Str

so here we can type winds colon and

we're going to insert a value using

Dollar open curly bracket Clos curly

bracket and here we're going to insert

the number of wins that we have which is

score. wins so we'll type score

dowins next we're going to show the

number of losses that we have so after

this

let's type a comma and losses colon and

insert another

value here we'll insert

score.

losses and finally we'll type a comma

and we'll display ties colon and

inserted value score dot

ties and this will display our score in

the popup so let's save this and give it

a try we'll click okay and then go back

to our Tab and play the

game so now on the second line we will

display the score one small issue here

is that we have a lot of spaces on the

second line so these spaces correspond

to the spaces here when we use

multi-line strings these Extra Spaces

will show up in the popup so to remove

these SP cases we can just remove them

in the code like this now if we

save press

okay and play the game it will show our

score on the second line without those

Extra Spaces at the front let's press

okay we're going to add one more feature

to this project if we go back to Super

simple. Dev we have a reset score button

which will reset the score back to zero

when we click it let's add this button

in our project so we'll scroll

up and inside the

HTML We'll add a button with the code

less than button greater than and inside

the button we'll have the text reset

score and now when we click this button

we'll run some code using the onclick

attribute equals double quotes and then

in here we're going to write some code

to reset this score back to

zero so one way we can do it is because

this score is an object we can use dot

notation to change everything back to

zero so we can type

score. wins and make it equal to zero

we'll also type

score. losses and make it equal to Z and

finally

score. ties and make it equal to

zero now let's

save and go back to our

Tab and play the game a few times to get

a

score let's press okay and press reset

score and then play the game again and

you'll notice that the score started

from zero again so that's how we create

the reset score button we just set all

of these properties back to

zero and that's it that's how we add a

score feature to our rock paper scissors

project using an object to save the

score let's press

okay and we're going to learn more

details about objects let's go back to

objects.

HTML and what open the tab for this

file and let's also comment out the

previous code using

slashstar and at the

bottom star

slash and

save now let's scroll to the bottom and

we'll do some

setup so first let's create a variable

with const we'll name it Product 2 and

make it equal to another object

inside this object we have the property

Name colon and the string

shirt and we're going to console.log

this object so

console.log Product 2 and

save so the next detail we're going to

learn about objects is another way to

access the values

inside we previously learned the

notation to do this for example

console.log product

to.

name this will access the value

associated with the name

property in JavaScript we have another

way of accessing values inside objects

which is using square brackets so we'll

create a new line and type console

do

log product 2 and this time we'll type

square

brackets and then inside the square

brackets we'll have a string with

name so this is called bracket notation

and this does the same thing as dot

notation up here it gets the value

associated with the name property if we

save these two lines of code both access

the string shirt which we see here so

when do we use the bracket notation

instead of the dot notation bracket

notation lets us use properties that

normally don't work with do notation for

example at the bottom we can type

console.log Product 2 and then use a DOT

and try to access a property called

delivery-time if we

save this property will give us an error

and that's because JavaScript thinks

that this Dash is a minus sign and it's

trying to do math so in order to use a

property like this we have to use

bracket notation so we're going to

replace the dot with square

brackets and and turn this into a

string now if we

save it no longer gives us an error and

because delivery time does not exist in

the object we get the value

undefined so using bracket notation we

can also add values to the object when

we create it so here we can add a

comma and we'll add another property

using bracket notation and a string

delivery-time and a colon and then a

value like the string one

day if we

save this lets us add a delivery-time

property to this object so as you can

see bracket notation lets us use

properties that normally don't work with

DOT

notation another feature of bracket

notation is that between the brackets we

don't just have to use a string we can

use a variable a calculation or anything

that results in a

value so you might be wondering which

one should we use do notation or bracket

notation we usually use do notation by

default because it's shorter and easier

to read but if we need to use properties

that don't work with do notation then we

use bracket not

notation now a shortcut here is when we

create the object if we only have a

string between the brackets the brackets

are actually optional so we can just

type this if we save the code will still

work okay the next detail we're going to

learn is that inside an object we can

save any type of value so this includes

numbers strings booleans

as well as other objects because

remember objects themselves are also

values for example we can type a comma

and add a property called

rating colon and then an object open

curly bracket close curly bracket and

inside this inner object we can add more

properties like stars colon 4.5

this is how many stars a product has and

then a comma and a property called count

colon

87 this is how many ratings a product

has so this is called a nested object or

an object inside an object we can use

nested objects to make our values more

organized so inside the product the

number of stars that has and the number

of ratings that it has are both related

to a rating so it makes sense to group

them together further inside the

product now to access values inside the

inner object we just use the dot

notation or bracket notation multiple

times for example at the bottom we can

type

console.log product

2 dot

rating this will get the value

associated with rating and this is an

object so we can use the dot notation

again

count so this will get the count inside

the rating object which is this value

right here so if we save it will display

87 and finally another type Ty of value

we can put in an object is a function so

in this object let's type comma and

another property

fun colon and we're going to create a

function here so let's type

function and we'll name the function

Function One brackets and curly brackets

and then inside the function we're going

to have some JavaScript code like usual

so

console. log the string

function inside

object this saves a function inside the

object and this works because a function

is actually just another type of value

in JavaScript but we'll learn more about

this feature of functions later in this

course for now just know that functions

are also values and we can save them in

an object to access this function we can

use the dot or bracket notation as usual

so at the

bottom we can type the object Product 2

and then a DOT and then the property

fun so this will access the value

associated with the fun property which

is a function and because this is a fun

function we can call it as usual using

brackets if we

save this will run the function here and

it will display function inside object

into the

console so when we save functions inside

an object this is called a method and

we've actually been using methods this

whole time

console.log is actually a method

console is an object provided by

JavaScript and log is a function that is

saved inside the console

object if we go to the bottom and type

console.log type of

console and

save this will confirm that console is

just an object and if we change this to

console.log and

save this will show us that console.log

is a function so log is a function that

is saved inside the console object so we

call this a method another example of a

method is math.random which we used in

the rock paper scissors project math is

also an object provided by JavaScript

and random is a function saved inside

the math object so we call math.random a

method as well so we've actually been

using objects and methods all throughout

this course and now we understand all

the code that we've been using so far

next we're going to learn about builtin

objects so the console object and the

math object are known as builtin objects

because they are built in to the

language they provided by the

language we're going to learn two more

built-in objects called Json and local

storage and we will use these objects to

improve our rock paper scissors project

let's start with the Json built-in

object this object helps us work with

something called

Json Json stands for JavaScript object

notation the easiest way to understand

Jason is it's BAS basically a syntax

it's a similar syntax to a JavaScript

object but it has less features for

example the code on the left uses

JavaScript object syntax and the code on

the right uses Json syntax so one

difference is that all properties and

strings must use double quotes in Json

Jason does not support single quotes

another difference is that Json does not

support function functions so as you can

see Json is basically a syntax that's

similar to a JavaScript object syntax

but with less

features so why would we use Json syntax

instead of a JavaScript object

syntax a JavaScript object only makes

sense in

JavaScript on the other hand Json syntax

can be understood by almost every

programming language so Json syntax is

more un

Universal for this reason we use Json

when we send data between two computers

that might use different programming

languages we'll learn how to do this

later in the course we also use Json

when we store data we'll learn how to

store data in this

lesson now that we understand what Json

is let's learn about the built in Json

object the Json object helps us convert

a JavaScript object to Json for example

let's convert our object product two to

Json so we'll create some new

lines and we'll type the Json object do

stringify and Open Bracket close bracket

so stringify is a method of the Json

object so it's a function that is saved

inside this object and we can call this

function using

brackets between the brackets we can

give it a JavaScript object we want to

convert like Product

2 this will convert the object into Json

so now let's

console. log the

result and

save and in the console it will display

the product using Json syntax if we we

scroll up you'll notice that the

function that we saved in the object is

not inside the Json and that's because

Json does not support

functions so one thing to note about

stringify is that it actually results in

a string so at the front if we type type

of and

save it will tell us that the result

that it gives is actually a

string so if we remove

this and

save now this Json string is ready to be

sent to another computer or to be saved

in

storage next let's learn how to convert

the other way from a Json back to a

JavaScript object to do that we'll use

another method in the built-in Json

object called json.parse

at the end we'll type Jon

dop

pars and

brackets and between the brackets we can

put a Json string that we want to

convert so we actually have a Json

string up here so let's just make a copy

of this we'll select it

rightclick

copy and let's create an extra variable

to make it more clear const Json string

and make get equal to right click and

paste and now let's convert this Json

string back into an object by putting it

into

pars and finally we console.log this

result so

console.log and

save and json. pars will turn the Json

string back into a JavaScript object so

that's the built-in Json object it helps

us convert back and forth between a

JavaScript object and

Json now we're going to learn the next

built-in object called local storage

local storage is used to save values

more permanently so far we've been

saving our values in

variables however variables are

temporary they only exist on the current

page if we refresh the page or close the

page all the variables are deleted for

example if we go back to our rock paper

scissors

project and open the tab for this

project and we play a few

games and play it again so we have two

games if we refresh the page

notice the score starts from zero again

and that's because when we refresh the

page all of these variables are deleted

and the score gets reset back to zero

however if we press okay and go to

superimple

dodev and we refresh the page and we

play the

game notice that the score doesn't start

from zero it starts from the previous

score even though we refreshed the page

and that's because this project saves

the score in local storage and local

storage doesn't get deleted when we

refresh the

page now let's learn how to use local

storage in our project let's press okay

and we'll go back to our code and we'll

scroll down to where we update the

score so here after we update the score

we're going to save it in local storage

but first first let's learn how local

storage works so at the bottom here

we're going to type the local capital S

Storage

object to save a value inside local

storage it has a method called set item

so we can type dot set capital I item

and brackets because this is a method or

a function saved inside the object

object and we're going to give two

strings to this method the first string

is a name this is how we're going to

access the value that we save later so

let's use the string

message as the name and we'll type a

comma and then we'll type the value that

we want to save into local storage so

local storage only supports strings so

let's save the string

hello inside local

storage if we

save and then go back to our Tab and

play the

game it will run all this code and save

this string into local storage now let's

learn how to get this string out of

local storage we'll press okay and we'll

scroll to the

top and when we first load the page

we're going to get that value out of

local local storage by typing local

capital S

storage. getet item this

time and

brackets so the get item method gets a

value out of local storage and we're

going to give it one string so this

string is the name that we used earlier

which was message so we'll type the

string

message now let's console log this

result so

console.log and a bracket at the

end and

save it will get the value that we saved

earlier out of local storage so we saved

the string hello and that's exactly what

gets displayed in the

console so using local storage we were

able to get the value that we saved

earlier even though we refresh the

page now let's save our score into local

storage so it doesn't get reset when we

refresh the page so let's scroll to the

bottom and instead of using the name

message we're going to use the name

score to save our score and instead of

the string

hello we're going to save the score

object now one problem here is that

local storage only supports strings so

we need to convert our object into a

string and we actually learned how to do

this earlier using json.stringify

so at the front we can type

json.

stringify and then brackets around the

score and this will convert the

JavaScript object score into a Json

string and then it's ready to be saved

in local store

so if we save this and then play the

game it will run this code and save our

score into local

storage now let's press

okay and then's scroll up to the

top and now instead of getting the

message we're going to get the score out

of local storage if we

save now when we load the page we're

able to get the score that we saved from

last time as a Json

string the last step is instead of

resetting the score to zero every time

we're just going to use the score from

local storage before we do that remember

that this is just a string so we need to

convert this back to an

object we also learned how to do this

earlier using json. pars so at the

front we can type

json. pars and then Open Bracket and at

the end a close bracket and it will

convert this back to an object if we

save it will convert the score from a

Json string back to an object so now we

can use it up here so instead of doing

this we'll remove it and replace it with

this code so right click cut

and then here right click and

paste and we'll remove

console.log and

save so now when we load the page it

will load the score from local storage

if we play the

game notice that the score doesn't start

from zero it starts from the score that

we had last time let's review what we

did step by step first when we update

our score in this code after we update

the score we're going to save it in

local storage using local storage. set

item now local storage only supports

strings so we have to convert our score

object into a Json string using json.

stringify and then after we've saved

this into local storage when we load the

page up here we're going to load the

score that we just saved from local

storage using local storage. getet item

and the score was saved as a Json string

so we need to convert it back into an

object using json.parse

so that's how we use the Json object and

the local storage object to save our

score more

permanently let's press okay

okay and the last feature we're going to

add is when we click the reset score

button we also need to remove the score

from local storage otherwise if we press

reset score and

refresh and then play the game it will

just grab the old score from local

storage so reset score doesn't really

work here let's press okay and fix this

issue so here in the set score button at

the end we're going to remove the score

from local storage so we'll type

local

storage and then a method called do

remove item and

brackets and between the brackets we're

going to tell local storage which value

we want to remove so we're going to

remove the score so we'll type the

string score

if we

save and we click the reset button and

then we refresh the page and try to play

the game

again unfortunately it now gives us an

error so what is happening here so

remember that we remov the score from

local storage so now when we load the

page this actually doesn't exist when

something doesn't exist in local storage

it's going to give us a value called

null

and at the

bottom if we try to access any property

on null it will give us an error so

that's what we see here so how do we

solve this problem if we scroll

up one way to solve this problem is that

if there is no score in local storage

we're going to give it a default value

let's look at how we can do that so

after this line we're going to check if

the score is null we can do that using

an if statement if brackets and curly

brackets and we'll check if score is

equal to

null and if it is equal to null we're

going to give this a default score so

inside the curly

brackets we'll just make the score equal

to the default object we had earlier

which was

wins zero and then

losses zero and

ties

zero and remember if we need to reassign

a variable we have to change it from

const to let if we

save the score will be null because we

removed it earlier and now this will

give it a default score so everything

should work as before

if we play the

game you'll notice that the score starts

from zero or this default score and

everything is working again so that's

how we create the score feature in the

rock paper scissors project as well as

the reset score

feature next we're going to use some

shortcuts to simplify our code so these

shortcuts are things that we learned in

the Boolean lesson so remember that null

is a falsy

value that means it will behave just

like false so a shortcut we can use here

is instead of checking if the score is

equal to null we can also remove this

and check if not

score so not score does the same thing

as checking if it's null if the score is

null not score will flip it into true so

both of these will return true if the

score exists it's an object then both of

these will return false so instead of

checking if a value is equal to null we

can just use the not operator as a

shortcut now also from the boolean's

lesson we have an even shorter shortcut

for doing this so notice here that this

code basically sets a default value if

the score doesn't exist in the boolean's

lesson we learned a technique called the

default operator which is exactly what

we need here so on this line we can

remove the semicolon and type

or and then a default value so we want

our default value to be this object so

let's select it and then

rightclick copy

and then here right click and

paste and I'll select these lines and

press shift tab to remove and indent and

I'll add a semicolon back at the

end so the way that the default operator

works is that if the left side is truthy

so in this case we have a score it will

use the left side if the left side is

falsy or in this case the score is null

then we will use the right side as a

default value so this does the same

thing as this code below but it's just a

shortcut so now let's comment out this

code using

slashstar and at the bottom start slash

so we'll leave it here just for

reference and then

save and if we click reset score again

and

refresh and play the

game it will still work so this is a

perfect situation to use the default

operator to simplify our

code so let's press

okay and that's all we're going to do

for this project in this

lesson now let's move on and learn more

details about objects the first thing

we'll learn is the value null so null is

one of the falsy values in JavaScript

it's similar to the value undefined they

both represent that something doesn't

have a value so what's the difference

between null and undefined we use null

when we intentionally want something to

be empty for example in the previous

lesson we learned that if a function has

parameters we can give the parameter a

default value if the parameter is

undefined

it will use the default value however if

we set this parameter to null it will

not use the default value and it will

just use null so null means we

intentionally want something to be

empty in most cases though null and

undefined work the same way okay so the

next detail about objects we're going to

learn is called

autoboxing let's go back to objects. HT

HML and open the tab for this

file and let's also comment out the

previous code so our console doesn't get

too messy so

slashstar and at the

bottom star slash and

save so let's scroll

down we learned in this lesson that

objects can have properties and methods

so you might be surprised to learn that

other values also have have properties

and methods for example at the bottom

we're going to type

console.

log the string

hello and then the dot notation and a

property called

length so strings can also have

properties the length property tells us

how many characters or letters are in

this string so hello has five letters so

if we save the length property will be

five here's another example we'll type

console.log the string hello and then

the dot notation and a method this time

2 capital u upper Capital C case and

brackets so this string also has a

method called two

uppercase and this method gives us a

copy of the string with all letters

capitalized or in

uppercase if we save it will give us

hello in capital

letters so as you can see simple values

like strings can also have properties

and

methods so now you might be wondering

these are strings not objects how can

strings have properties and methods the

answer is that JavaScript has a special

feature called Auto boxing JavaScript

automatically wraps this string in a

special object first and this object has

the property length and the method to

uppercase so this is done automatically

we don't see the special object that's

wrapped around this string so this

feature is called

autoboxing because JavaScript automat

automatically wraps the string in an

object like a

box so autoboxing also works with other

types of values like numbers and

booleans the only thing is that auto

boxing does not work with null and

undefined it would just give us an

error The Last Detail we're going to

learn about objects is a really

important detail and that is objects are

references to demonstrate let's create a

new variable with an object so

const object one and make it equal to an

object inside this object let's have a

property

message colon and the string

hello so you might think that when we

create an object like this we create a

value that has other values inside and

we save the whole thing and a variable

however this actually works a little

differently when we create this object

the actual value is created somewhere in

the computer's memory and this variable

actually just gets a reference that

points to that location in the

computer's memory this is like a

shortcut on your computer a shortcut

points to where the actual file or

folder is so there's no way to actually

see this reference but just just know

that this is a reference and the object

is somewhere else in the computer's

memory so the reason it works this way

is to make the language more efficient

for example below this line we can

create a variable const and call it

object 2 and make it equal to object

one so this code doesn't actually make a

copy of the object it this makes a copy

of the reference that points to the

object so this makes a language more

efficient because if we had a really big

object here it's not good to copy the

entire object over and over again

instead Javas just copies the reference

which is much faster this is called copy

by

reference now that we learned that

objects are actually references let's

learn some interesting behaviors of

references so at the bottom here we're

going to change the property message in

this object we can do that by typing the

object object

1. message property and make it equal to

something else like the string good

job and now if we

console. log object one

and

save notice that we were able to change

the message property even though we

created object one with const and that's

because this variable just contains a

reference that points to the object so

const prevents us from changing the

reference in the variable but it doesn't

prevent us from reaching into the

reference and changing the object that

it's pointing to so just be careful when

you're working with with objects even

though we use const we can still change

the values inside the object another

interesting behavior is that on this

line we're not actually copying the

object into this variable we're copying

the reference so object two actually has

the same reference as object one they

actually point to the same object in the

computer's

memory so at the bottom if we type

console

log object 2 and save you'll notice that

for object two the message property was

also changed even though we only changed

object one the last interesting behavior

is that we can't compare objects

directly for example let's go to the

bottom and we'll create a new object

using

const object 3 and we'll make it equal

to an object and then inside we're going

to have these same values as object one

so we'll have the property

message and the value is the string good

job so now let's try comparing object 3

to object one so here we'll type console

do

log and check if object 3 is equal to

object

one if we

save it will tell us that these two

objects are not equal to each other even

though they have the same values inside

and that's because remember objects are

references so object 3 also contains a

reference and this code compares the

references and not the values inside the

object so because object 3 is a

different reference than object one

that's why this code results in

false if we

did

console. log and we check if object 2 is

equal to object

1 object two has the same reference as

object one it points to the the same

object in the computer's memory so if we

save this will tell us that these two

variables have the same

reference so just remember that when

you're comparing two variables that

contain objects you're actually

comparing the references not the values

inside if we want to compare the values

inside we would do that manually by

checking the message property against

this message property so don't worry

object references are a little confusing

at first but the more you work with it

the more you just get used to

it the last thing we're going to learn

in this lesson are some shortcuts for

objects so first let's make a copy of

object 3 we'll select the code and

rightclick

copy and then at the

bottom we'll scroll down and right click

and paste

and let's rename this variable to object

4 so now let's say that we want to get

the message property out of this object

we can do that by typing object

4.

message and now let's also say that we

want to save this in a variable also

called message so at the front we'll

type con

message and make it equal to this

value so now if the variable name and

the property name are the same we

actually have a shortcut for this to use

a shortcut we're going to type const and

curly brackets

message and make it equal to object

4 so this shortcut is called

destructuring this will take the message

property out of object 4 and save it in

a variable called message so this line

of code does the same thing as the code

above so let's comment out this line

using double slash and we'll just keep

it for reference so at the bottom if we

type

console.log

message and Save

it will display good job so the

destructuring shortcut took the property

out of the object and saved it in this

message

variable next we can use this

destructuring shortcut for multiple

properties for example let's add another

property to this object using comma and

we'll add a price property colon

$7.99 and now we can take the price

property out of this object by typing

after message a comma and

price so this will take the price

property out of the object and save it

in a variable called

price if we

console.log the

price and

save it will display $799

so that's the destructuring shortcut

it's an easier way to take properties

out of an

object the next shortcut we're going to

learn is called the shorthand property

so at the bottom let's create some new

lines and let's say we want to create a

new object so we'll type const and let's

name this object 5 and we'll make it

equal to an

object and inside ins this object let's

say we want to create a message property

so we'll type message colon and for the

value let's type the variable

message so what this does is that it

takes whatever is inside the message

variable and substitutes it into this

code so at the bottom if we

console.log object 5 and

save this object will have a property

called message and the value is whatever

is inside the message variable which is

good job so now we actually have a

shortcut for this code if the property

and the variable name are the same we

can actually just type it out once like

message so this code does the same thing

as message colon message and this

shortcut is called the shorthand

property so if we comment out this line

using double

slash and

save you can see that this shortcut

creates the same object that we had

before the last shortcut we're going to

learn is called the shorthand method so

at the end let's create a new property

comma and let's name it

method Po in and we'll save a function

in this property so we'll type

function and let's name it Function One

brackets and curly

brackets and inside this function let's

console.log

method and now here at the

bottom let's run this function by Ty

typing object 5. method so this will

access this function and we'll run it by

typing

brackets if we

save this will run the code in the

function and display method in the

console so we actually have a shortcut

for writing this so at the bottom we can

type method again and just type brackets

and curly brackets

console.log string

method so this code does the same thing

as the code above so these brackets will

create a function just like here so this

function name is actually not needed so

if we comment out these lines of

code and

save it will still display method in the

console because this is a shortcut for

these lines of code so this shortcut is

called the shorthand method

syntax and that's the end of this lesson

in this lesson we learned another type

of value called objects objects group

related values together we added a score

to our rock paper scissors game we

learned about built-in objects and used

the Json and local storage objects to

save our our score more permanently we

learned more details about objects like

null autoboxing and references and we

learned some useful shortcuts like

destructuring shorthand properties and

shorthand methods here are some

exercises to help you practice working

with objects

in this lesson we're going to learn one

of the most important features of

JavaScript called the document object

model or the Dom and we're going to use

the Dom to improve our rock paper

scissors project so first we'll create a

new file for this lesson let's go to our

code editor and click this icon to show

our files and then click this icon to

create a new file and we'll name this

file 09

dd.

HTML and press

enter next let's copy objects. HTML into

dom.

HTML so we'll click here to open the

file file and then click inside and then

type contrl A or command a to select the

code and then

rightclick

copy and in

here right click and

paste now let's hide these files and

we'll prepare this file for this lesson

so let's scroll to the

top and we'll change the title to

Dom and let's delete all the JavaScript

code from the previous

lesson now let's save this file and

we'll open it in the browser by right

clicking open with live

server and let's also open the console

on this page we'll right click click

inspect and then click the console

and now we can close the previous

tabs as well as the previous code for

now and for this lesson we're going to

do an extra step in the setup inside the

body we're going to create a

button so here let's type the code less

than button greater than and inside the

button we'll have the text

hello now let's

save and we should have a button on the

page and now we're ready to learn the

document object model or the Dom in the

previous lesson we learned about objects

which group multiple values together we

also learned about builtin objects which

are objects that are provided by

JavaScript some examples of built-in

objects are console math Json and local

storage the Dom is another builtin

object called the document object so

let's go to our script element and we're

going to type

document so this is a built-in object

provided by JavaScript and we've

actually seen this document object

before in the first lesson one of the

first pieces of code that we learned was

document dot body do inner Capital

HTML equals the string hello and

semicolon so this code removes

everything on the page and replaces it

with the text hello if we

save it will remove the button and just

put

hello and now that we learned objects in

the previous lesson we can fully

understand this

syntax document here is a built-in

object and this is the dot notation this

means we're accessing a property of the

document object called body now body is

also an object so we can use the dot

notation again to access a property of

the body object called inner

HTML and finally we use an equal sign to

change the inner HTML property to the

string

hello but as you can see there's

something very special about the inner

HTML property when we change this

property it also changes the web page so

this document object and the web page

are linked together let's do another

example we'll go to the end here and

press enter and we'll type the document

object again

and we'll use the dot notation again and

this time let's access the property

title and we'll change the title

property using an equal sign and we'll

change it to the string good

job if we

save changing the title property we'll

also change the title at the top of the

tabs here so now this says good job

again as you can see the document object

is linked to the web page so from these

examples it shows us that the document

object represents or models the web page

and that's why we call this feature the

document object model or the

Dom now that we know what the Dom means

let's learn the syntax rules for the Dom

so the Dom is just this built in

document object and this object works

the same way as any other object it

contains properties like body and title

that we can access using the dot

notation now the special thing about the

document object is that it is linked to

the web page that means if we change

certain properties in this object it

will also change the web

page now in addition to properties the

document object also has methods we can

use and we'll learn about them later in

this

lesson now that we understand the syntax

of the document object let's learn about

the properties and methods we can use

first let's comment out this previous

code using

slashstar star slash and we'll create

some new lines at the

top so the first property will we're

going to learn is called

document.title

so this property will give us the title

at the top of the tabs here so if we

console.log this property

console.log and

save this will give us the text at the

top which is Dom and that's what gets

displayed in the

console if we change the doc do. tile

property it will change the text at the

top of the tab so here if we type

document.title and make it equal to the

string

changed and

save now the title at the top of the tab

will be

changed so as you can see the title

property is linked to the title at the

top of the tab

we can use it to get the title and we

can also use it to change the

title next we're going to learn another

property called

document.body so let's go into our

code and let's type

document.body now document.body is a

very special property so this will

literally get this body HTML element

element and put it inside our

JavaScript so let's actually console.log

this to see how it works

console.log Open

Bracket and then close bracket and

save and inside the console it will tell

us that

document.body is the body HTML element

and if I hover over this it will tell us

that it is a exactly the body on our

page if I expand this you can see that

this code is exactly the code that we

have here and this shows us one of the

most important features of JavaScript we

can have HTML elements inside

JavaScript the document object or the

Dom combines JavaScript and HTML

together and it gives JavaScript control

of the web page

okay so now that we have an HTML element

inside our JavaScript what can we do

with it a really important thing to know

is that when an HTML element is inside a

JavaScript like this the HTML element is

converted into a JavaScript object so

for example if we do

console.

log type of document do

body and

save it will tell us that the body HTML

element is just an object when it's

inside

JavaScript so just like any other object

this has properties and methods we can

use so one useful property of the body

element is inner HTML which we saw

earlier so down here let's type

document dot body dot inner Capital

HTML so the inner HTML property controls

all the HTML inside the body that's why

it's called inner

HTML so if we access this property it

will give us all the HTML inside the

body so let's console.log to

confirm

console.log and

save and inner HTML will give us all of

this HTML inside the body

element and if we change the inner HTML

property it will change the HTML inside

the body element so let's create a new

line and we'll type document

dot

body do inner Capital

HTML and we'll change it to the string

changed so this will replace all of the

HTML inside the body with a text changed

if we

save that's exactly what it does and we

can actually confirm this by going into

the elements tab so this tab is for HTML

and CSS we can find the body element

expand it and you can see all of the

HTML that we had before was replaced

with

changed and don't worry about this part

this part is just added by live server

after so this shows that inner HTML

gives us control of all the HTML inside

the body we can get this h HTML and we

can also change this

HTML now another feature of inner HTML

is that we can replace this HTML with

new HTML code not just text so for

example instead of just text we can

replace it with the code less than

button greater than and also less than

slash button greater than so so this is

HTML code for creating a button and

inside the button let's put the text

good

job and now this code will replace all

the HTML inside the body with this new

HTML if we

save it removes all the previous HTML

and this new HTML creates this button so

using this inner HTML property

JavaScript can replace the HTML inside

the body to whatever we want we have

full control of the web

page all right now we're going to learn

a method of the document object that we

can use as a reminder a method is a

function that is saved inside an

object so we're going to learn a very

important method called document. query

selector we just learned that

document.body lets us get the body

element and put it inside our

JavaScript document. query selector lets

us get any element from the page and put

it inside our JavaScript let's give it a

try so first we'll comment out the

previous code using

slashstar and star

slash let's create some new lines at the

top

and let's type

document. query capital S

selector and

brackets so document. query selector

lets us get any element from the page

and put it inside our

JavaScript between these brackets we're

going to put a string this string tells

JavaScript which HTML element to get

from the page

so if we type

button this will get the first button

element from the page and put it inside

our JavaScript so let's console.log this

to

confirm

console.

log close bracket and

save and let's go back to our

console now it will tell us that

document. query selector got this button

element and put it inside our JavaScript

which you can see in the console and if

I hover over this button element it will

tell us that it is exactly the button on

the page so that's what document. query

selector does it can get any element

from the page and put it inside our

JavaScript this string tells it which

element to get if we type button it will

get the first button element from from

the page if we type

body this will now get the first body

element from the page so it will do the

same thing as

document.body but for now let's just

change this back to Button as an example

and

save so remember when an HTML element is

inside JavaScript it's just a JavaScript

object so this button element

is also just an object and it has

properties and methods we can

use every HTML element actually has a

property called inner

HTML which lets us control the HTML

inside the element so for this button

element let's type at the end dot inner

HTML and this will give us the HTML

inside the button if we

save it will give us

hello and again if we change the inner

HTML property it will change the HTML

inside the button so let's make a copy

of this code we'll select it and

rightclick

copy and down

here right click and

paste and let's change the inner HTML

property using an equal sign and the

string

changed so this will only change the

HTML inside the button which is here to

changed if we

save you can see that the text inside

the button is now changed a little

syntax shortcut I'm going to show you is

that for the dot notation we can

actually put it on multiple lines so we

can type document. query selector and

then put doin HTML on a separate line to

make it easier to read and make sure to

put a tab at the front so that we know

it's a continuation of the previous

line okay so using document. query

selector we can get any element from the

page put it inside our JavaScript and

then we can control the h HML inside

that element and this allows us to only

change the parts of the page that we

need next what if we have two buttons on

the page so let's go up here and we'll

create another button using less than

button greater than and we'll have the

text

second

button and

Save so now we have two buttons on the

page but document. query selector will

only get the first button on the page

how do we get this second button the

solution is that we're going to add an

attribute to this button called the

class attribute so in the opening tag

we're going to type space class equals

double quotes So the class attribute

sort of adds a label to this button so

inside the double quotes we're going to

label this button a JS dash

button and now that we labeled this

button we can select it using document.

query

selector so at the bottom here we'll

type

document. query selector again and

brackets and we'll type A String inside

and this time we're going to start with

a DOT when we start with a DOT this

means that it's going to look for a

class rather than an element name so

we're going to look for the class

js-

button and now document. query selector

will select an element with the class JS

button which is this element here so

let's confirm this by

console. logging this

code and

save and now you will see that this code

gives us the second button on the page

so using a class attribute and then

starting with a dot in query selector we

can get any specific element from the

page and put it in our

JavaScript by the way when we start with

a DOT this is called called a class

selector and this is also used in CSS to

style elements with a specific class in

fact anything we use in CSS can also be

used in this

string and also a common practice is to

start the class with

js- to make it clear that this class is

being used in

JavaScript and again HTML elements are

JavaScript objects so this second button

is also just an object and remember

objects are values and we can save them

inside a variable so instead of

console.log let's create a variable

using const and we'll name the variable

button capital E

element we usually end the variable name

with element or LM to make it clear

clear there's an HTML element inside

this

variable and finally we'll type an equal

sign to save this element and we can

remove this extra

bracket and now if we console.log this

variable

console.log

button

element and

save it will tell us that the second

button was Sav saved inside this

variable so using the Dom we can get

HTML elements from the page put it

inside a JavaScript and then save it in

a variable so the Dom combines

JavaScript and HTML together it gives

JavaScript full control of the web

page all right now that we learned how

to use the Dom let's do some practical

examples so I've actually prepared some

projects that we can do for this lesson

to open these projects we'll go to our

browser and create a new tab at the

top and here we'll type

super

simple. SL projects

slod and press

enter on this page we'll be working on

three projects the YouTube subscribe

button the rock paper scissors project

we've been working on for the last few

lessons and this Amazon shipping

calculator and you'll notice that these

projects modify the web page so we're

going to be using the Dom to create

these projects and in the next lesson

we're going to use CSS to style these

projects and make them look nice and you

can preview that by clicking

here so using CSS we can make the sub

subscribe button look like the actual

subscribe button on YouTube and if we

click this link to see the rock paper

scissors game you'll see that we'll make

it look really nice with these icons but

for this lesson we're only going to

focus on the functionality and not the

styling so let's go back to the projects

we'll click back and click back

again until we're at projects sdom

and we're going to create the

functionality for these projects first

so before we start let's create a new

file just for these projects we'll go to

our code editor and click this icon and

then click this icon to create a new

file let's name this file 09

dd-

projects. HTML and press

enter now let's copy dom. HTML into this

file so we'll open it and then click in

here and type control a or command a to

select the code and then

rightclick

copy and in

here right click and

paste now let's close our files and

we'll prepare this file

so let's scroll up and we'll change the

title to Dom

projects and let's remove our HTML but

keep the script

element and we'll also remove the

JavaScript from

before finally let's save this file and

we'll open it in the browser by right

clicking open with live server

and let's also open the console just in

case right click click

inspect and then click the

console all right we're ready to start

with the projects let's go back to super

simple

dodev and we'll start by creating the

YouTube subscribe button let's actually

press refresh to get it back to normal

and when we click this button it will

change to subscribe

red first let's create the HTML elements

for this project we'll go to the body

we'll create some new

lines and let's create the paragraph

first we'll type less than P greater

than and inside the paragraph we'll have

the text

YouTube

subscribe

button and now let's create the button

so on the next

line we'll type less than button greater

than and inside the button

subscribe now let's save and go back to

our

Tab and now we have the HTML elements

that we need so now let's make this

interactive with JavaScript and remember

we have a process for this first we'll

figure out what steps we need to do this

is called an algorithm and then we'll

convert these steps into code so the

steps that we need here are when we

click this button if the text is

subscribe we'll change it to

subscribed otherwise we'll change it

back now let's convert these steps into

code let's go to our button element and

we're going to add an onclick attribute

we'll type space on click equals double

quotes and inside here we'll write some

JavaScript so first we need to get the

text inside the button and we learned

how to do this earlier we can use

document. Query selector to put this

button into our JavaScript and then use

inner HTML to get this HTML inside the

button so in our code let's type

document. query

selector brackets and a string and as we

learned we're going to use a class

attribute to select this specific button

so in the opening tag let's add a class

attribute and let's make the class

js-

subscribe Dash

button and then inside document. query

selector we're going to type a DOT to

select a class and we're going to select

the class

js-

subscribe Das

button and now let's console.log this to

confirm that we got this button so at

the front

console.log and

save and now let's click our

button and it will show us that

document. query selector got the button

on the page so now let's save this

button in a variable so we can use it

later instead of

console.log let's type const to create a

variable and we'll name it

button

element and make it equal to this

result so now that we have the button

inside our JavaScript we're going to

check if the text inside the button is

subscribe to check the text we can use

an if statement so at the bottom here

we're going to type if brackets and

curly

brackets and inside this condition let's

get the text inside the button so we'll

type button

element do inner Capital

HTML and we're going to check if it's

equal to subscribe so we'll type triple

equal the string

subscribe now if it is equal to

subscribe inside the curly brackets

we're going to change the text in the

button to

subscribed so let's type the code

button

element do inner Capital HTM L and we'll

change it with an equal sign to the

string

subscribed and the last step is

otherwise we'll change it back so we'll

add an else to this if

statement else and curly brackets and

inside we're going to change the text

back to

subscribe so let's type

button

element. inner Capital

HTML and make it equal to the string

subscribe and

save now before you try out this project

make sure that the text inside the

button has no spaces or new lines around

it and it looks like this and I'll show

you why in a second let's go to our

project and try it out so when we click

this button it will change to the text

subscribed if we click it again it will

go back to the original text so that's

how we create the Subscribe button

project using the Dom so now let's go

back into our code and I'll show you why

if we add new lines

and some spaces around this

text there's actually going to be some

problems so if we save this

code and then go back to our project and

click the button again you'll notice

that it no longer changes the text and

that's because now we have a bunch of

spaces around this text and these spaces

will show up in inner

HTML and now inner HTML will not equal

exactly

subscribe so how do we solve this

problem when there are spaces around our

text to solve this we're going to use a

different property of an HTML element so

instead of the inner HTML property we're

going to use the property inner capital

T

text so inner text will give us the text

inside this element but without all the

spaces around it

so now this will equal exactly

subscribe if we save and go back to our

project and click it again it'll start

working again so that's the inner text

property of an HTML element it gets us

the text without the extra

spaces so before we move on to the

second project I'm going to show you how

to make our code

cleaner right now we're mixing a HTML

and JavaScript together so to make our

code cleaner and easier to read we're

going to separate the JavaScript code

and to do that we're going to put this

code in a function

instead so inside the script

element let's create a function using

function and we'll name the function

subcribe brackets and curly brackets

and inside these curly brackets we're

going to move all of this code so let's

select this

code and we'll right

click

cut and in here right click and

paste and if we need to fix the

formatting we can select these lines and

press tab a few times and now that we

have this function we're going to go to

the onclick attribute and and we're

going to call this function so we'll

type the function name

subscribe and

brackets so this will run all the code

inside the function so it will do the

same thing as before except now our code

is cleaner because we grouped all the

JavaScript code at the bottom and we're

no longer mixing as much HTML and

JavaScript

together now let's move on to the second

project we'll go back to superimple

dodev and we're going to work on the

rock paper scissors project so let's

click this

link and it will show us the next

version of this project so you notice a

few changes here the first change is

that we're going to show the score on

the page instead of in a popup and the

second change is that when we click one

of these buttons to play the game it

will show us the result and the moves

that we picked on the page rather than

in a

popup let's create a new file for this

rock paper scissors game for this lesson

so let's go to our code

editor and we'll click this icon and

click this icon to create a new file and

we'll name this

09-

rock- paper Das

scissors.

HTML and press

enter and let's copy the previous rock

paper scissors which is here we'll click

here and type control a or command a

right click

copy and here right click and

paste and let's hide our

files and let's save this F file and we

can also close 08 rock paper scissors

and finally we'll open this in the

browser by right clicking open with live

server now we're ready to begin the

second project so let's go back to the

project at super simple Dev and we're

going to start by putting the score on

the page so to do this we're going to

need somewhere to put the score so let's

create an HTML element for this we'll

scroll up to our

HTML which is

here and after the scissors button let's

add a paragraph element where we're

going to put our score so less than P

greater

than and let's add a class attribute so

we can select this element in our

JavaScript so in the opening tag we'll

type space class equals double quotes

js-

score now that we have a class let's get

this element in our

JavaScript so let's just do it down here

so we'll type

document.

query

selector brackets and a string and then

we're going to type a Dot and we're

going to select the class js- score so

js-

score so this will get the paragraph

element from above and put it inside our

JavaScript and now let's put the score

inside the element to do that we can use

inner

HTML dot inner Capital

HTML and we'll make it equal to the

score if we scroll

down we actually create the score down

here so we can actually just copy this

string so we'll select it

rightclick

copy and let's scroll

up to here and I'll actually put this on

a separate line to make it easier to

read and now here we're going to type a

string using back

ticks and inside the string we're going

to rightclick and

paste so this will put the score that we

used to have in our popup inside this

element so inside this

paragraph if we

save and then go back to our

tab you can see that now it displays the

score on the page now before we move on

I want want to point something out with

HTML so remember that our reset score

button was beside our other buttons and

now it's below them so what determines

if an element appears beside something

or below something so the paragraph

element Here is known as a block element

a block element will always take up an

entire line by itself so this line

already has some buttons so the

paragraph will take up the entire line

under the buttons that's why this text

appears under the buttons and not beside

them and also because a block element

like this paragraph takes up this entire

line the next button has to appear below

it so that's why we get this layout here

so this is just a short review of

layouts if you want to learn this in

more detail you can check out my HTML

and CSS full course in the video

description all right the next feature

we're going to do is if we play the game

we also want to update the score right

now if we play it doesn't update it on

the page let's fix this in our

JavaScript so let's go down to where we

update the score so we'll scroll

down which is right here we update the

score and save it in local storage and

after we do this we're also going to

update the score on the page so we can

actually use the same code that we used

above which is here so let's make a copy

of this code

rightclick

copy and down

here right click and

paste and I'll add a tab at the front if

we save and then try out our game we'll

click a move press

okay and now you'll notice the score

also updates on the page so let's go

back into our code and do some cleanup

so you notice that this code is the same

as the code we had above and this is a

great situation to use a function to

reuse this code so at the bottom here

let's create a function using function

and we'll call it

update

score

element brackets and curly

brackets and we'll move this code into

the function so we'll select it right

click

copy and in here right click and

paste and now instead of writing this

code multiple times we're just going to

call the function

update score element and

brackets this will run all the code

inside the function so it does the same

thing as before except we can reuse the

code so let's scroll back

up and instead of typing out all this

code again we can just use our

function

update

score element

and

brackets now let's

save it will display the score on the

page at the start and when we click a

move and click okay it will update the

score on the page so the last feature

we're going to do in relation to the

score is when we click the reset score

button we also want to update the score

on the

page right now if we click it it doesn't

actually update it

so let's go into our code and let's go

to the reset button which is here and

after we reset the score we're going to

call that function again

update

score element and

brackets if we

save and now let's play the game and

press okay so we have a score and if we

click reset score it will reset

everything back to zero so now we

finished the score let's go back to

super simple

Dev and play the

game and now we're going to work on this

section we're going to show the result

and the moves that we picked on the page

so first let's create some paragraphs

for these as well we'll go to our

HTML and above the score

let's add a less than P greater than

this is going to be the result so let's

give it a class of

js-

result and let's create another

paragraph less than P greater than and

we'll give this one a class equals

js- moves

now let's use the Dom to put the result

and the moves in these paragraphs feel

free to pause the video if you want to

try it yourself first so let's scroll

down to where we display the

result which is here so we display it in

a popup and instead of a popup we're

going to get the paragraph and put this

result inside the paragraph so we'll

type

document. query

selector brackets and a string and we'll

type a DOT and select the class

js-

result and then dot inner Capital

HTML and we'll change this to

result and now let's also display the

moves so we'll type some new lines and

document. query selector again brackets

and a string dot

js-

moves do inner Capital

HTML and make it equal to this text

right here so let's type a template

string because we're going to insert our

Moves In inside the string and we'll

Type

U and we'll insert the player move

dollar curly

brackets Player move and then a dash and

then the computers move so dollar curly

brackets again and

computer

move computer at the end so now that

we're displaying everything on the page

we don't need this popup at the end so

we can actually delete this

popup all right now let's

save and go back to our

Tab and play our

game now it will show the result and the

moves that we picked on the page instead

of in a popup let's play it again to

make sure it works and finally when we

click reset score it it will reset

everything back to zero and that's it

now we're displaying everything on the

web page using the

Dom now let's move on to the third and

final project we'll go back to Super

simple.

deev and we'll click back to go back to

our projects and we're going to create

this third project here which is an

Amazon shipping

calculator the way this works is is that

inside this text box we're going to type

the cost of an order in dollars if the

order is under

$4 for example

$25 and we click

calculate it will add $10 of shipping

and display the total down here but if

we type a cost that is over

$40 like 50 and press

calculate it will be free shipping so so

it will display the same total down here

so let's learn how to create this using

the

Dom let's go back to our 09 Dom projects

file and we'll start by creating the

HTML

elements so under our subscribe

button let's create this paragraph using

less than P greater than

Amazon shipping

calculator and next let's create this

text box so the HTML element for a text

box is called input so we'll type less

than input greater than so the input

element is special because it doesn't

require a closing tag this is called a

void

element and lastly let's create the

button so here we create less than

button greater than

calculate now let's

save and open the tab for this file

which is right here and we have the text

the text box and the button that we need

now one other thing we're going to add

is that in the final project if we don't

have anything in the text box we're

going to have this gray text so this is

called a placeholder to add a

placeholder to a text box we're going to

use the placeholder attribute so inside

our input element we're going to type

Space Place

holder equals double quotes and inside

the quotes we'll put the text we want as

the placeholder which is cost of

order and

save now if we go back to our project we

now have a placeholder in our text box

that disappears when we start

typing so that's all the HTML that we

need now let's work on the JavaScript

and again we'll figure out what steps we

need to do so when we click this button

we're going to get the text inside the

text box if the amount is below $40

we'll add $10 of shipping and then we'll

display the total on the page let's

convert these steps into code so we'll

go to our button and add and onclick

attribute and inside here let's also

create a function to separate our

JavaScript code like we did before so in

the script we're going to create a

function function

and let's name it

calculate total brackets and curly

brackets and inside on click we're just

going to call the function so

calculate

total

brackets the next step is to get the

text inside the text box so first let's

get this input element and put it inside

our J JavaScript to do that we can use

document. Query selector again so we'll

add a class to this input so we can

select it class equals

js-

cost-

input and then inside our JavaScript

we'll use

document.

Query

selector brackets and a string and a Dot

and this class

js-

cost-

input so this code will get the input

element and put it inside our JavaScript

let's confirm by

console. logging the

result and

save and now when we click the calculate

button it will give us

the input element from the page let's

save this input element in a variable so

we can use it later instead of

console.log we'll use const and we'll

name the variable

input element and make it equal to this

element and remove the extra

bracket and next we need to get the text

inside the input element so so far in

this lesson we've been using the

property inner HTML to do this however

for input elements you notice that there

is no HTML inside so for input elements

we're going to use a different property

called

value so at the bottom here we're going

to type

input

element.

value this is how we get the text inside

a text box

so let's console.log this to confirm

that it works so we

console do

log and

save and now let's type something in the

text box like 50 and click

calculate and input. value will give us

the text inside the text

box let's save this text in a variable

so so we can use it later con and we'll

name the variable cost and make it equal

to the text in the text

box the next step is to check if this

cost is under

$40 if it is We'll add

$10 so down here let's type if brackets

and curly

brackets and inside the condition we'll

check if cost is less than

40 and if it is inside the curly

brackets we'll do cost equals itself

plus $10 of shipping and remember when

we change a variable we have to switch

from const to

let and finally we're going to display

the total cost on the page so let's

create a paragraph where we can display

the cost so down here we'll create a

paragraph less than P greater than let's

give it a class

js- total Das cost and now inside our

JavaScript let's use

document. Query selector brackets and

string and we'll Type A Dot and the

class

js- total Das cost and we're going to

put the cost inside the paragraph we can

use dot inner Capital

HTML and make it equal and let's use a

template string so back ticks and we'll

have a dollar and we're going to insert

the cost using dollar and curly brackets

cost now let's save and try out this

project so first we'll type a cost that

is over

$40 like 50 if we press

calculate we're not going to add $10 of

shipping and we'll display the same

total on the page now let's try a number

under

$40 like 25 and press calculate

and this number doesn't look right it's

saying that we have to pay

$2,510 so what's going on here let's go

into our code and let's use console.log

to figure out what's wrong so first

let's console.log the cost to make sure

that we're getting the right number from

the text box so down here

console.log the cost

and save and then let's Type 25 again

and press

calculate and it will give us 25 so

we're getting the correct text from the

text box now let's console.log down here

to see if the math is working so we'll

type

console.

log

cost and

save and let's try 25 again and

calculate

and down here when we add 10 this is

where things go wrong and it results in

20510 so it's not doing math properly

here so let's check if cost is a number

to make sure that it's doing math so

here we'll type

console.log the type of

cost and Save

let's Type 25 again and calculate and

aha it's telling us that the cost is a

string so this is actually not a number

it is a string that's why it's not doing

math so remember from the strings lesson

when we add a string with a number

JavaScript will automatically convert

this number into a string and combine

them together that's that's why it just

combines 25 and 10 here this is called

type

coercion so whenever we get a value from

the Dom like this the value will be a

string so in order to do math we have to

manually convert this string into a

number to do that JavaScript has a

builtin function called number so before

this code we're going to type capital n

number Open Bracket and close bracket so

the number function takes whatever's

between the brackets and manually

converts it into a number so now if we

save and we Type 25 and press

calculate the cost is now a number and

it will do the math properly and give us

35 so remember whenever we get a value

from the Dom the value will be a string

so if we want to do math with it we have

to manually convert this value into a

number first so now let's remove the

console. logs that we used to figure out

this

problem and

save okay we're going to add one more

feature to this project let's go back to

superimple

dodev and inside the text box we're

going to Type 25 and press

enter so pressing enter will also

calculate the total and display it on

the page so let's learn how to create

this feature so if we go back to our

code so far in this course we've been

using the attribute

onclick which runs some JavaScript when

we click an element HTML has another

attribute we can use called on key down

which runs JavaScript when we press a

key down on our keyboard so inside the

input this time let's add the attribute

on key down equals double quotes and

then inside here

console. log and the string

typing so now every time we type in the

input it will console.log this message

let's save it and give it a try we'll go

to the tab for this file and then inside

the text box we'll type some numbers and

you can see that every time we type

something it will run this code and

display this

message so that's how we do something

when we type in an element so clicks and

key Downs are known known as events on

click and on key down are known as event

listeners they check for events and runs

JavaScript when those events happen now

in addition to clicks and key Downs

there are many other events we can

listen for in

JavaScript okay so now let's figure out

what steps we need to do for this

project when we press a key down in the

text box we're going to check if the key

is the enter key if it is we'll do the

same thing as the calculate

button so how do we know what key we

pressed inside on key down we're

actually given a special object called

event so instead of this string let's

remove it and we'll

console.log

event so this is an object that's

provided to us by JavaScript and it

contains information about the event

every event listener including on click

also gets an event object if we

save and type in this text

box it will show us that event is this

object and inside the object it has a

bunch of information including the key

that we typed so here let's use the

event object and we'll get dot key and

save so now inside this text box if we

type something it will tell us the key

that we pressed and if we press

enter it will tell us that the key is

enter so the next step is to check if

the key is enter and we can do that

using an if statement so in our

code we'll type a new line

if brackets and curly brackets and

inside the condition we'll check if

event. key is equal to the string

enter if it is equal to enter we're

going to do the same thing as the

calculate button so we can actually just

use this function again inside the curly

brackets we'll type calculate

total and

brackets and

save so now let's go back to our project

and type 25 enter and it will calculate

the total and display it on the page so

that's how we create this keyboard

feature of this project lastly let's

clean up our code and move this into a

function like the rest of our code so

inside the script

element let's create a new function

using

function and we'll name it

handle cost key down brackets and curly

brackets and let's move this code into

the function we'll select it

rightclick

cut and in here right click and paste

if we need to fix the formatting we can

select these lines and press Tab and

let's remove this

console.log and now up here we're going

to call this

function

handle cost key down and

brackets now the last thing we have to

do is that event does not exist inside

this function so we have to put the

event object into the function

and remember to put a value into a

function we can use a

parameter so between these brackets we

can create a parameter called event and

now to save something inside this

parameter we're going to go up to these

brackets and type

event this will take the event object

and put it inside the function where we

can use it just like a variable so now

if we

save and try out the project 25 enter so

this still works and now we finished all

three projects in this lesson so in the

rest of this lesson we're going to learn

some more details about

JavaScript in the last project we

learned how to manually convert a string

into a number using the number function

we can also convert the other way from a

number to a string so let's go to the

top of the script

element and we can type capital S string

and brackets so the built-in string

function will convert a value into a

string between the brackets we can put a

number like 25 and this will convert the

number into the string

25 the next detail we're going to learn

is a special behavior of

strings So Below this line we can type

console do log the string

25 minus

5 so if a string only contains a number

and we subtract multiply or divide

JavaScript will automatically convert

the string into a number so this gets

converted into the number 25 minus 5 and

if we save it will do math and give us

20 so this is another example of type

coercion or automatic type

conversion however it's not recommended

to do math with strings like this

because adding Works differently for

example on a new line let's type

console.log the string 25

+ 5 and

save this will convert the number into a

string and combine them together into

255 so because adding strings Works

differently the best practice is always

do math using numbers don't do math

using strings if we need to we can

manually convert the string into a

number using the number function like we

did here the last thing we're going to

learn in this lesson is another built-in

object called the window object so in

this lesson we learned about the

document object the document object

represents the web page the window

object represents the browser so let's

go into our script element and Try It

Out Below this we'll Type

window so so this is the window object

and it represents the browser because it

represents the browser everything inside

the browser is inside the window object

so let's think what's inside the browser

well the web page is inside the browser

so the document object is inside the

window object if we type

window.

document this will give us the same

document object that we've been using in

this lesson so what else is part of the

browser well the console is also part of

the browser so here if we type

window.

console this will give us the same

console object we've been using in this

course so we can actually do

console.log and the string window

and

save and this will do the same thing as

console.log what else is part of the

browser well popups are also part of the

browser so if we type

window.

alert this will give us the same alert

function that we've been using in this

course to create

popups however you might have noticed

that we never Type window window. doent

or window.

console.log and that's because the

window object has a shortcut we don't

have to type window dot at the front we

can just type document or console and

JavaScript will automatically add window

dot at the front for us so window is a

built-in object that represents the

browser we don't have to type out window

dot ourselves because JavaScript adds it

for us automatically but it's still nice

to know how this works behind the scenes

and that's the end of this lesson in

this lesson we learned about the

document object model or the Dom which

allows JavaScript to fully control the

web page we learned how to use document.

Query selector to get elements from the

web page and put them inside our

JavaScript we learned how to use inner

HTML to modify the HTML inside an

element we worked on three projects

using the Dom we learned how to make

elements interactive with the keyboard

using on key down and we learned some

more details about strings as well as

the window object which represents the

browser here are some exercises you can

do on your own to practice using the Dom

in this lesson we're going to add CSS to

all of our projects and we're going to

finish our rock paper scissors project

CSS is a different language that changes

the appearance of our website it's one

of the three languages that we use to

create websites so first let's look at

the projects we're going to work on in

this lesson we'll go to our browser and

create a new tab at the

top and here we're going to type

super simple

dodev SL projects slash

Dom Das

with-

CSS and press

enter so these are the same three

projects we created in the previous

lesson except this time we're going to

add CSS to make these projects look nice

let's start by creating a copy of the

Project's HTML file from the previous

lesson we'll go to our code

editor and click this icon to show our

files and then here we're going to

select

09-- projects we're going to right

click

copy and down here right click and

paste and let's rename this file by

right-clicking

rename at the end we're going to remove

copy and at the beginning

we're going to change it to 10 and press

enter now let's hide our

files and we're going to open 10 Dom

projects in the browser by

right-clicking open with live

server now we can close our previous

tabs as well as the previous code from

lesson 9 which is this file and these

two

and now we're ready to add CSS to our

projects we'll start with the YouTube

subscribe button let's go to the tab for

our

project and we're going to style this

button first so we reviewed CSS in

lesson 4 and one of the ways we can

write CSS code is using the style

element so inside the head section we're

going to create an element using less

than style greater than so the style

element lets us write CSS code inside so

inside here we're going to write

button open curly bracket close curly

bracket so the code in front of the

brackets is called the CSS selector this

tells the computer which elements we

want to style or change the appearance

so button will style all button elements

on the page but in this situation we

only want to style the Subscribe button

because the calculate button will be

styled differently so to style a

specific element we can use the class

attribute so if we look at our button

currently it already has a class of JS

subscribe button but this class is being

used by our JavaScript a good practice

is to add a different class that will be

used by

CSS so an element can have multiple

classes we just separate them with a

space so inside this class attribute

we're going to type space and add

another class

subcribe dash

button now this element has two classes

and we're going to use this second class

in our

CSS so to style a specific class we're

going to remove button and we're going

to type a DOT so starting with a DOT

means we're going to style a class

rather than an element name so we'll

style the class

subscribe Das

button which is this button right here

and now inside these curly brackets

we're going to tell the computer how to

style this button for example border

colon none and

semicolon if we

save this will remove the border from

the button so it no longer has a border

like this button so that's how we style

a specific element with CSS we add a

class to the element and then inside CSS

we start with a DOT and the class and

between the curly brackets the code on

the left is called the property

this tells a computer what we want to

change on the right is called the value

this tells a computer what we want to

change the property to we separate the

property and value with a colon and we

end the whole thing with a semicolon so

this is also called a property value

pair as a reminder this is just a review

of CSS if you want to learn CSS in more

detail you can check out my HTML and and

CSS full course in the video

description so we just added one style

to this button we're going to add more

Styles so that it looks like our final

design to make this easier I'm going to

rearrange my windows and I'm going to

put the final design at the bottom and

then our project at the

top this will make it easier to compare

the two

designs next to make it look like the

final design we're we're going to style

our element one by one let's go back to

our

code and press enter and next let's

change the background color to Black to

do that we'll type

background Das color colon black and

semicolon and

save now our button has a black

background let's keep going one by one

we change the text color to white next

so in our code we'll type color colon

white and semicolon and

save now if you're wondering how I know

all these properties you can usually

find them by searching in Google just

make sure you search for what you are

trying to

do let's keep going one by one the next

thing we'll change is we're going to add

spacing on the inside of the button in

CSS space on the inside of an element is

called padding so we'll create a new

line and we'll use the property

padding Das toop colon

10px and

save so this will add space on the

inside of the element called the padding

at the top of 10 PX

so the PX here means pixels a pixel is a

unit of measurement in computers your

screen is made up of many small little

squares each of these squares is called

a pixel so a pixel is the smallest thing

that you can have on your screen screen

sizes are measured in pixels images and

video sizes are also measured in pixels

and don't worry the more you work with

pixels the more you'll get used to how

big a pixel is so in this example 10

pixels is equal to this amount of space

and it looks pretty close to the final

design so let's keep going we'll add

space on the inside of the element at

the bottom this time so we'll create a

new line and type padding Dash bottom

colon

10px again and Save

and that adds space at the bottom of the

element of 10

pixels next let's increase the space on

the left and the right we'll go into our

code and add padding Das left colon 10

pixels and padding Das right colon 10

pixels let's save

and it added some extra space on the

left and right but I think our final

design has a little more space on the

left and right so let's go back and

increase our padding so instead of 10

let's try 15 on both

sides so we'll

save and now the spacing looks close

enough to the final

design so in CSS it's normal to do some

trial and error to get the styling right

let's keep styling this one by one next

we'll make the text thicker or bold so

let's go into our code and to change the

thickness of the text we'll use the

property font Das weight colon

bold let's

save and that will make our text bold so

we're almost there now let's make the

corners rounded look like in the final

design we'll go back to our CSS and the

property for making the corners round is

called

border Das

radius and we'll make it colon 5

pixels let's

save and you can see that it made our

Corners round so the pixels here tells

the computer how round we want the

corners to be the higher the pixels the

more round it will get

so if we change this to 10 pixels and

save it will make the corners even more

round so let's change this to something

really big to make it completely round

we'll change this to 50 pixels and

save and now our button is completely

round the last style we're going to add

is in the final design if we put our

Mouse over the button it turns into this

hand the icon so we call this a pointer

and we're going to do the same thing in

our project so let's go to our code and

to create that pointer icon we're going

to use the property

cursor colon

pointer and let's

save and put our Mouse over the button

and you'll notice it turns into this

hand pointer icon and that's it now our

subscribe button looks like the final

design next let's click the Subscribe

button you'll notice that it only

changes the text but if we click the

final

design it also changes the background

color and the text color so we're going

to learn how to change the CSS when we

click a

button let's go back to our code and

this time we're going to scroll down to

our

JavaScript which is here so we learned

in the previous lesson we can get HTML

elements from the page and put them

inside our JavaScript and we also

learned that these HTML elements are

just JavaScript objects and they can

have properties like inner text and

inner

HTML every element has another property

we can use called class list class list

gives us control of the class attribute

so one solution we can do is when we

click the button we can add a class and

then this class will have different

styles so let's see how we do that in

our code we'll scroll down to the

Subscribe function and when we click the

button and make the button subscribed

we're also going to add a class so let's

create a new line and we'll type button

element dot class capital L

list so class list itself is an object

which means it has properties and

methods we can use one method is called

add which adds a class to an element so

after this let's type dot add and

brackets and now inside these brackets

we're going to put a string so this

string is a class that we want want to

add when we click this button let's add

a class called

is-

subscribed and

save so now every time we click this

button it will add a class to the button

called is- subscribed let's give it a

try first we'll rightclick on the page

and then click

inspect and we'll go to the elements Tab

and I'll rearrange my windows so you can

see

it and then inside the HTML pay

attention to the class of the button now

when we click the

button it's going to add an extra class

called is- subscribed so that's what

this line of code does and now that this

button has the is subscribed class we

can style it in our CSS so let's go back

to our code

and we'll scroll up to our

CSS and here we'll type dot to style a

class and we'll style the class is-

subscribed

is-

subscribed and curly

brackets and now inside these curly

brackets let's change the background

color to Gray and the text color to

Black

Background Das color colon

gray and then color colon

black and make sure to type these Styles

below the Subscribe button Styles so

that these Styles will override the

Styles

above now if we

save and then click our

button it will add the is subscrib class

and now this button will get our new

styles that we added here so that's one

way to change the CSS when we click a

button all right now I'm going to move

this back to the

top and notice that our background color

is different from the final design the

final design uses a much lighter gray so

how do we get this exact color to do

that we're going to open the elements

tab again so on this page we're going to

rightclick click

inspect and then click the elements

Tab and I'll rearrange my windows so we

can see

it so in this section in the style

section we can see the CSS that the

element has so first let's actually find

this button which is right here and

we'll click

it and here it will show us the CSS that

this button has and it will show us the

background color that we should use so

let's make a copy of this color and put

it into our code

rightclick

copy and here we'll remove it and

rightclick and

paste now let's

save and go back to our project and try

it

out and now we get get the exact same

color as the final design so by the way

this color is known as an RGB value RGB

means red green and blue and computers

can create any color using a combination

of red green and blue so the first

number here is how much red we want in

our color the second number is how much

green we want and the third number is

how much blue we want

each number goes from 0 to

255 Zer means less color and darker 255

means more color and lighter so this

color here uses 240 for all of the

colors so it's close to 255 and will

give us a very light gray color that you

see

here next if we go back to the final

design and we click our button again

it will change back to the original

style so we're going to create this

feature in our project as well so one

way to do this is when we click the

button again we can remove this class so

let's scroll down to the

bottom to the Subscribe function and

when we click the button and we change

it back to subscribe we can remove this

class to do that class list has a

another method we can use called remove

so let's create a new line and we'll

type

button element do class capital L

list dot

remove and

brackets so this does the opposite of

add it will remove a class from this

element so inside the brackets we'll

type a string and the class we want to

remove which is

is-

subscribed and

save now let's try out our project we'll

click the button it will get the class

is subscribed and get the extra Styles

and now when we click the button again

it will remove the class and it will

remove the extra

Styles so notice here that when we add a

class we just type the class name we

don't type a DOT and the class name like

we did for query selector typing a DOT

only makes sense in query

selector next we're going to style the

text on the page let's scroll up to our

CSS and one thing we can do is to style

all the paragraph elements on the page

using this code P and curly brackets

however we're going to use a better

solution instead of styling all the

paragraphs we're just going to style the

body

element when we change the text in the

body element it will change the text in

the entire page so inside these curly

brackets let's change the text here so

we're going to use a different style of

text this is called a font to change the

font font we're going to use this

property font Das

family colon and we'll change it to

aial which is what I used in the final

design so let's

save and this will style all the text

inside the body and change the font to

aial and a good practice is to write any

styles for the body at the top so if we

need to we can override it later so

let's move these to the top we'll right

click

cut and then up

here create some new lines and right

click and

paste and we're going to add one more

style before moving on let's add some

space between the Subscribe button and

the second project so earlier we learned

that space on the inside of it element

is called padding space on the outside

of an element is called margin so inside

our subscribe button at the

bottom let's add a property called

margin Das bottom colon 30 pixels and

save so this will add space on the

outside of the element at the bottom of

30 pixels

now let's move on and style the Amazon

shipping calculator with

CSS again we'll add a class to these

elements and then style them in our

CSS let's scroll down to the text box

which is the input element and we're

going to add another class by typing

space and let's use the class cost Das

input and now we're going to style this

in CSS so let's scroll up and here we'll

style the class using dot cost Das

input and curly

brackets and inside we'll style this one

by one let's look at our final design

and see what styles we need so first

let's change the text size because our

text is a little smaller than the text

here so the change the text size

we're going to use Font Das size colon

and let's try 15 pixels and

save and now our text looks close enough

to the final

design next let's add some space inside

the text box so remember space inside an

element is called padding so we're going

to type

padding Das

top of 10

pixels padding Das bottom also 10

pixels and let's add padding to the

left 10

pixels and padding

dasr of 10 pixels so this will add a

space on the inside of our text box in

every direction if we

save now it looks just like the final

design now I'm going to show you a

shortcut for padding that will save us

some typing so if we create a new line

we can actually use a property called

padding and colon and then type 10

pixels this padding property let us add

padding on multiple sides at once if we

type one value here like 10 pixels it

will add 10 pixels to every side so this

line does the same thing as these four

lines above so let's actually comment

this out using

slashstar and star slash and

save and you can see that this one line

of CSS did the same thing as the other

four lines of CSS so this shortcut can

save us some typing

next let's move on and style the

calculate

button again we'll add a class to this

button so we can style it so in this

button let's add a class

attribute class equals

calculate Das

button now let's style this in our CSS

by scrolling up and here we'll type Dot

calculate dash

button and curly

brackets and inside these curly brackets

we're going to style this button one by

one so let's start with the background

color so we'll type

background Das color colon green and

semicolon and

save next let's change the text color to

white

so we'll type color colon

white and save

again okay let's keep going and we'll

remove the border around this button so

we'll type

border colon

none

save next let's make our text a little

bigger like in the final

design so we'll type font Das

size and make it 15

pixels and

save okay so now let's add the space on

the inside of the button so we're going

to use this shortcut again we'll type

the padding

property colon and this time we're going

to give it two values separated by

spaces 10

pixels and maybe 50 pixels so it's

easier to see what this does so when we

give two values to padding the first

value is the vertical padding so the top

and bottom the second value is the

horizontal padding or left and right if

we

save so you can see that the left and

right has a lot of padding which is 50

pixels so now let's make this match our

final design so instead of 50 pixels

let's bring it down to 15 pixels and

save okay so that looks pretty close

let's also increase the padding on the

top and bottom so that the text box and

the button line up with each other like

in the final

project so let's change the vertical

padding to maybe 12 pixels and

save the last thing we'll style for this

project is when we put our Mouse over

the button it turns into the pointer

icon so to create this we're going to

use the property

cursor colon

pointer and save and give it a

try and that's it we just finished

styling the Amazon shipping calculator

so now let's give this a try we'll Type

25 in the text box and press calculate

and at the bottom it will add $10 of

shipping and show

$35 finally we're going to style the

last project in this lesson which is the

rock paper scissors project and this

will finish the project let's go back to

superimple dodev and we'll scroll down

on this page and then click this link to

show the final design for rock paper

scissors so I'll rearrange my windows so

we can see

this and we're going to change the

buttons to these nice big icons for each

of the moves and when we click a move it

will show the result in bold and show an

icon of the move that we picked and the

move that the computer picked so we're

going to make this project look really

nice now let's get started I'm going to

rearrange my windows back so we have it

at the bottom and let's create a cop

copy of the rock paper scissors project

for this lesson we'll go to our code

editor and click here to show our

files and we're going to make a copy of

09- Ro paper scissors so let's click

this file and then

rightclick

copy and down here right click and

paste and we'll rename this file by

right-clicking

rename and at the end we'll remove copy

and at the beginning we'll change it

from 9 to 10 and press

enter now let's click here to hide the

files and we can close the 09

file and let's open the 10 rock paper

scissors file in the browser so we'll

right click and then open with live

server and I'll move this tab to the top

here so we can see it side by side so

let's start by styling the body we want

to make the background color of the

entire page this dark gray color we'll

go into our code and let's create a

style element so we can write some

CSS inside the head let's type less than

Style

greater than and then inside here we're

going to style the body so we'll type

body and curly

brackets now inside here we're going to

change the background color so

background-color colon and we're going

to get the color that we see here by

right clicking click

inspect and then go to the elements tab

Tab and I'll rearrange it so we can see

it and then here we'll find the body

element and click it and in this style

section we can find the background color

that we need so let's select

this and

rightclick

copy and in

here right click and

paste and a semi colon at the end let's

save and I'll move this back to the

corner and now our project has the same

background color as the final design

next let's make the text color white so

in our CSS we'll use the color property

and colon white and semicolon and save

and that will make our text White

next let's change the style or the font

of this text we'll type font

dasam colon

aial which is what the final design uses

and

save all right now let's style these

elements one by one to match the final

design we'll start with this paragraph

at the top so inside the paragraph

element

let's add a class so we can style it in

CSS we'll add class

equals let's call this the

title and then in our CSS we can style

this class by starting with a DOT and

then

title and curly

brackets so let's make our title really

big like the final design we'll change

the font Das size colon 30 pixels and

save so that looks close enough next

let's make the text bold in our CSS

we'll use Font D weight colon bold and

save now let's move on to installing the

buttons so first we're going to need

these images in our project and I'll

show you how to get them we'll put our

Mouse over the rock image and we'll

rightclick and we'll click save

image and now we're going to find the

folder that contains all of our code so

for me it's on the

desktop and it's this folder right here

so I'll double click this folder and

then leave the file name as the default

rock- emoji and click save

and now in our code editor if we click

here we should be able to see the rock

image let's do the same with the paper

and scissors image so we'll hover over

it rightclick save

image and in the same folder that

contains our code we're going to save

the paper image and finally rightclick

save image and we'll save the scissors

image

all right now that we have these images

in our code editor let's learn how to

load them onto the page so we can do

this using an HTML element so we'll go

back to our HTML code and we'll scroll

down and inside the button we're going

to add an image element so let's type

less than IMG and greater than so this

is the image HTML element it loads an

image onto the page the image element

doesn't require a closing tag this is

called a void element now to load an

image we're going to add an attribute to

this element called

SRC so SRC stands for Source it tells a

computer which file or image to load so

let's look in our

project for this button we're going to

load rock- emoji.png

inside the source attribute we'll type

rock-

emoji.png

so what this does is it will look for

the file with this name beside the HTML

file and it finds it right here and it

will load it onto the page if we

save now inside our button it loaded the

rock

image right now this image is too big so

let's use CSS to decrease the size of

this image we'll hide the files and

let's give a class attribute to the

image element so we can style it so

we'll type class equals and let's call

this a move Das

icon and I'm also just going to add some

new lines to make the code a little

easier to read so we'll scroll up to the

CSS and we're going to style this class

using dot move Dash icon and curly

brackets and let's decrease the height

of this image we can use the property

height colon and a pixel value 50 pixels

and Save

so this will make the height of this

image 50 pixels and it will also resize

the width automatically so that the

image keeps its shape so this size looks

pretty close to the final design so we

can move

on another feature of the source

attribute is that we can put our files

into folders so let's open the files by

clicking

here and let's say that we want to

organize all of our images into a folder

so we're going to create a folder by

clicking this

icon and let's name this folder

images and we're going to drag these

images into this

folder and drag this in

here and in

here now unfortunately you can see that

the image doesn't load anymore and

that's because if we look at our code

Source tells a computer to look for this

file beside this HTML

file and right now there is no file

called rock- emoji.png because we put it

in a folder so to tell the computer to

look inside this folder we're going to

type the folder name at the start which

is

images and then we're going to type a

slash to go into the images folder and

then look for this file which is right

here if we

save the computer is now able to find

this image and load it onto the web page

so this feature is called file paaths we

can tell the computer to look for a

folder beside the HTML file like images

and then use a slash to tell it to go

into the folder and look for a file

now let's use this code to load the

other images onto our page so for the

paper image we're going to go to this

button remove the text and then create

an image element less than IMG greater

than and we'll give it an attribute

Source equals and we'll locate the image

it is in the images folder so we'll type

images and then slash to go into the

folder and we'll load the file paper-

emoji.png

so

paper-

emoji.png

and

save so our image is really big let's

give it the same class that we gave the

rock image so we'll add a class equals

move Dash icon and

save so these Styles get applied to all

elements with the class move- icon so it

applies to both of these

elements now let's do the same thing for

the scissors button we'll remove the

text and we'll replace it with an image

element and we'll give it the source

attribute images

slash

scissors Das

emoji.png

and we'll also give this a

class of

move- icon to resize the images like up

here let's

save and now we have all the images that

we

need now let's make these buttons look

like the final design we we scroll

up and let's add a class to these

buttons so we can style them with

CSS so we'll add class equals and let's

use

move-

button and for this button We'll add the

same class class equals

move-

Button as well as for the third

button class = move-

button now let's scroll up to our CSS

and we're going to style this class

using move- button and curly

brackets so first let's change the

background color to match the background

color of the page so we'll use

background Das color colon and we'll use

a special value called

transparent and this will make the

button see- through if we

save now these buttons are

see-through next let's add this white

border to our buttons so we'll use the

Border

property colon and we're going to give

it three values the first value is our

border width or how thick the border is

let's use one pixel for now the second

value is the Border style and we'll use

solid because it's a solid border other

values we can use here are dotted or

dashed and the third value is the Border

color so we're going to use

white and semicolon at the end and

save and that will add a border so let's

make our border a little thicker like

the final design we'll change this first

value which is the Border width to three

pixels and

save okay so that looks pretty close now

let's change the size of our buttons

usually we use the padding to add space

on the inside of an element but in this

case our images have different sizes so

we're going to use width and height to

set an exact size so so in our CSS we'll

type

WID colon and let's make it 100

pixels and

height and also 100 pixels and

save so it looks like our final design

is a little bigger than what we have

here so let's increase the width and the

height so let's try 120 pixels and Save

all right so that looks pretty close now

let's make these buttons round and the

property for that is called border Das

radius

colon and to know how much we need to

make it round we can set it to half of

the width or the height so we'll set it

to 60

pixels and

save okay so it's coming along really

well and lastly we're going to add some

space between the buttons so remember

that space outside of an element is

called margin so let's add some margin

on the right so we'll

type

margin

dasr colon and maybe 10 pixels and

save and finally when we put our Mouse

over the button it turns into a pointer

so the property for that is cursor colon

pointer and save and now our buttons

match the final design so let's keep

moving and style the next part of the

project which is the result and the

moves if you don't see this here you can

just play the game and it'll give us a

new

result so to make this easier to style

we're going to go into our code we're

going to find the result which is here

and we're going to add some fake results

like you

win let's save and now we have this

result and we're going to style it so

let's give this a class of

result and then in our

CSS we're going to style the class dot

result and curly brackets

so let's make the text bigger we're

going to use Font Das size colon and

maybe 25 pixels and

save okay that looks pretty good let's

make the text bold so we use Font Das

weight colon

bold and

save and finally we're going to add

extra spaces between this and the

buttons so we'll add

margin-top and maybe 50 pixels and

save okay so I think that looks close

enough now let's style the moves and

again we'll scroll

down and we're going to add some fake

moves in here so it's easier to style so

we'll Type U

and then an image so let's use the less

than image and the source

attribute and let's just load the rock

image and the scissors image for the

computer so to load the rock image we'll

look inside the images folder slash to

go into the folder and then rock-

emoji.png

so

rock- emoji

PNG and greater than and we'll add

another image less than image source

equals Images slash the scissors

Emoji scissors Das

emoji.png

and greater than and finally the text

computer

computer let's save

and this will create some results

although the images are really big so we

can use the class move icon to resize

them to be the same size as the buttons

so for both of these images let's add

the

class

move-

icon and here as well class equals

move- icon and Save

and now our images look

good next let's style this score section

so the only thing we need here is to add

spaces between these two so in this

score element let's add a class of

score and we'll scroll up and style this

element using DOT score

brackets and let's add some margin at

the top

so

margin-top colon 50 pixels and

save and let's compare it and it looks

like our final design has a little more

spacing than this so let's change this

to 60 pixels and

save and that looks close enough and

finally we'll style the reset score

button so let's go back to our HTM

ml we'll add a class to this button so

here class equals reset

dcore Das

button so at the top we'll type dot

reset

dcore

Dutton curly

brackets and we'll make the background

color white so background dasc color

colon

white and let's also remove the border

from our button using border colon

none let's save and see how it

looks and then let's increase the size

of this text because the final design

looks a little bigger so we'll add font

Das size colon 15 pixels and

save now let's add some extra space on

the inside of the button so that's

padding padding colon and we'll give it

two values the first value is the

vertical padding let's use 10

pixels and the second value is the

horizontal padding so let's use 15

pixels and Save

and it looks like our final project is a

little shorter than our button so let's

change the vertical padding to maybe

eight and save and the last step is to

add the cursor pointer so here cursor

colon

pointer and

save and that's pretty much it we

finished styling our rock paper scissors

project so now I'm going to rearrange my

windows so we can see the entire design

and it looks really nice the last step

here is to remove these fake results and

use JavaScript to insert these results

instead so let's scroll

down and we'll remove this

result and let's actually copy this code

because we want our JavaScript to

generate this code so we'll right click

and

copy and let's scroll to the

bottom to where we insert the moves onto

the page which is here and instead of

this text we're going to rightclick and

paste the code that we had before and

this time instead of picking Rock every

time we're going to substitute this with

the player move so we're remove this and

because this is already a template

string we can insert a value directly

inside using dollar and curly brackets

and we'll insert the

player

move let's also insert the computer's

move in here so we'll remove this and

insert a value using dollar and curly

brackets and we'll insert computer

move and now that we're inserting this

with JavaScript we can scroll up and

remove the fake

result which is here so we can select it

and delete

it now let's

save and we're not going to have

anything in our results and when we

click a move it will show us the result

and also show us the moves that we

picked and that's it we finished the

rock paper scissors

project the last thing we're going to

learn in this lesson is how to organize

our code into different

files so notice that right now all of

our HTML CSS and JavaScript is in one

HTML file and this makes the code harder

to read because the file is bigger and

it mixes three different languages to

make our code more organized and easier

to read we're going to separate each

language into its own file so let's

scroll down and we'll start by

separating our JavaScript into its own

file we'll click here to show our files

and then click this icon to create a new

file and we'll name this file

10-

rock-paper-

scissors. JS and press

enter so when we end a file

withjs it tells the computer that this

file contains JavaScript code not just

text now let's go back to our HTML

file and we're going to move all of this

code into the Javascript file so we'll

select this

code and then we'll

rightclick and

copy and inside the Javascript file

we'll rightclick and paste

now let's

save and we'll go back to the HTML file

and we can delete all this JavaScript

code and now we're just going to load

our Javascript file on to the web page

to do that we can use an attribute of

the script element called SRC or source

so we'll make it equal and this does the

same thing as the image element it tells

a computer which file to

load if we type

10-

rock-paper-scissors

DJs this will look for a file called 10

rockpaper scissors. JS beside our HTML

file which is this file here and it will

run all the JavaScript inside this file

so it does the same thing as before

except now our JavaScript code is in its

own

file and this makes our code cleaner

because each file only contains one

language and each file also contains

less

code now let's go back to the HTML file

and

save and you'll notice that our project

works the same way as before we just

organized our code

better another feature of The Source

attribute is that it also uses file

paths so we can put this Javascript file

in a folder and we'll be able to find it

for example let's show our files and

let's create a new folder by clicking

this

icon and let's name this folder

scripts so this folder will contain all

of our JS files so we can drag this file

into the

folder and now we can locate it using

the source attribute by typing the

folder name which is scripts and then a

slash to go inside this folder and look

for this file and it will find it right

here if we

save everything works as

normal another feature is we can use

multiple script elements this lets us

split our JavaScript into multiple files

and then load them all onto the page

from top to

bottom next we're going to learn how to

separate our CSS into its own

file let's scroll up to our

CSS so we can do the same thing with CSS

so let's click the HTML

file and let's create a new

folder and we'll call this folder Style

and press

enter so this folder will contain all of

our CSS code let's click the folder and

we'll create a new file by clicking this

icon and let's name this file

10-

ro-

paper-

scissors. CSS and press

enter so ending the file with CSS means

this file contains CSS code and now we

can go back to our

HTML and move our CSS into its own file

so let's select all this

code and then right

click

copy and in here right click and

paste and save this

file now let's go back to our HTML

and we can remove this

code and we'll learn how to load our CSS

file onto our

website so we're not going to use the

style element for this we're going to

use a different element called the link

element so we'll type less than link

greater than and the link element

doesn't require a closing tag this is

another void element so the link element

uses two attributes the first attribute

is called

R means relation this tells a computer

what type of file we're loading so we're

going to set this attribute to style

sheet this means we're loading a CSS

file and then we'll add a second

attribute called

href so href tells a computer which file

we want to load

so this also supports file paaths so we

can type the Styles

folder this will look for a folder

beside the HTML called Styles which is

this one right here and then we'll type

slash to go inside the folder and look

for this CSS file which is

10- Rock Das paper Das scissors

CSS so this will load all the CSS inside

this file and apply it to our page so it

does the same thing as before except we

separated each language into its own

file if we save everything still works

and all the Styles get applied and just

like the script element we can also use

multiple link elements to load multiple

CSS

files so that's how we separate our code

into separate files using the script

element and the link element it makes

our code a lot easier to read because

each file contains one language and it

contains less code and that's the end of

this lesson as a final reminder the CSS

we learned in this lesson is just a

review if you want to learn CSS in more

detail you can check out my HTML and CSS

full course in the video

description so in this lesson we

reviewed CSS and added CSS to all of our

projects we learned about the class list

property which lets us control the class

attribute of an element we finished our

rock paper scissors project and we

learned how to organize our JavaScript

and CSS code into separate

files thanks for watching this course so

far if you want to support this channel

you can check out the premium version of

my courses just like this one where you

can get a certificate of completion and

a Better Learning platform if you're

interested in extra videos from me more

in-depth videos and behindth scenes

content you can check out these links

here you can also support the channel by

liking the video subscribing and sharing

this video with others thanks again and

let's continue with the course

here are some exercises to help you

practice using HTML CSS and JavaScript

together

in this lesson we're going to learn two

more features of JavaScript called

arrays and loops and we're going to use

these features to create this to-do list

project first let's create a new file

for this lesson we'll go to our code

editor and click up here to show our

files and this time make sure you have

one of these HTML files selected so we

don't create the new file in one of

these

folders so now we're going to click this

icon to create a new

file and we're going to name this file

11- arrays Das and Das

loops.

HTML and press

enter now let's copy the previous lesson

into this file so we'll click on 10 Dom

projects and and we'll type here and typ

control a or command a to select the

code and then

rightclick

copy and in

here right click and

paste now let's hide our files and we'll

prepare this file for this lesson so we

can scroll to the

top and we'll change the title to arrays

and

loops and let's remove all of the

CSS and we'll also remove the

HTML which is right

here and we'll remove all the

JavaScript now let's

save and we'll open this file in the

browser by right clicking open with live

server and let's also open the console

so we right click click

inspect and click the

console and now we can close the

previous

tabs and the previous code for

now until we just have the lesson 11

file now we're ready to learn arrays an

array is another type of value in

JavaScript and it represents a list of

other values so let's do an example and

create our first array we'll go into the

script element and we're going to type

open square bracket and closed square

bracket and inside the square brackets

we'll type a value like the number 10

and then we'll type comma and and

another value like the number 20 and

then comma again and a third value like

the number

30 so this is an array and it represents

a list of three numbers 10 20 and

30 now arrays themselves are also values

which means we can save them in a

variable so at the front we can create a

variable using const

and let's name it my array and we'll

make it equal to this array and we'll

add a semicolon at the end so now we

created a list of values and we saved

this list in this

variable let's create a new line and

we'll

console.log my

array and Save

and it will display the list of values

in the console so that's basically what

an array is it's a list of

values now to get a specific value in an

array we can use square brackets so

let's create a new line and we'll type

my array and square

brackets inside these brackets we'll put

a number like

zero this number represents the position

in the array so zero means the first

value if we

console do log this

code and

save my array Square braet 0 gives us

the first value which is 10 and that's

what's displayed in the

console now if we change this to

one this will get us the second value in

the array which is 20 if we save it

displays 20 so this number represents

the position in the array zero is the

first value one is the second value two

is the third value and so on we can also

change a value in an array also using

square brackets so let's create a new

line and we'll type my array

square brackets and let's say we want to

change the first value so we'll type

zero for the first value and we just

make it equal to something else like

99 now if we

console.log my array

again and

save you can see that this changed the

first value to 99

so that's basically how arrays work we

can access a value inside an array and

we can also change a value inside an

array now that we understand the basics

of arrays let's learn the syntax rules

to create an array we start with an open

square bracket and we end with a closed

square bracket inside we can put a list

of values and we separate each value

with a comma

we can also write an array on multiple

lines like this we just put the new

lines after the

comma Now to get a value inside an array

we can use square brackets and a number

like one this number is called the index

it represents the position in the array

that we want to get so the first value

is index zero the second value is index

one 1 third value is index 2 and so on

notice that the index starts at zero

this is called a zero indexed

array now inside an array we can put any

type of value for example let's create a

new line and we'll create a new array

using square brackets and inside we can

put the number one and then comma and we

can also put a string like

hello and another comma and we can put a

Boolean value like true and another

comma and we can even put an object like

Curly

brackets Name

colon

socks now an array itself is also a

value that means we can save arrays in

very variables like this or even save it

in an array for example in this array we

can add an array inside like 1 comma

2 next arrays have a weird behavior when

we try to check the type of an array so

on a new line let's type

console.log type of and then square

brackets one comma

2 and

save this will tell us that an array is

an object and that's because an array is

actually an object but it's just a

special type of object if we want to

check if something is specifically an

array we can use this code capital A

array dot is

array

brackets and inside the brackets we'll

put an array like square brackets 1

comma 2 so this will check if this value

is an array if we

console. log this

result and

save it will display

true and finally because arrays are are

just a type of object they also have

properties and methods we can use so one

useful property is called length so

we'll type

console.log my

array.

length this will tell us how many values

are in the array so my array has three

values so if we save

it will display

three next we'll learn a useful method

of an array called push this adds a

value to the end of the

array if we did my

array.

push

100 this will add 100 to the end of my

array if we console.log

my

array and

save you can see that 100 was added at

the

end the last method we're going to learn

for now is called do splice this removes

a value from an array for example my

array do

splice and

brackets and a splice takes two numbers

the first number is the index that we

want to remove so let's say we want to

remove the first value which is index

zero the second number we give to splice

is the number of values we want to

remove if we give it one it will remove

one value at index zero if we give it

two it will remove two values starting

at index zero so for now let's just

remove one value

and let's create a new line and

console.log my

array and

save you can see that splice removed the

first value from the array or index0

which was

99 all right now that we understand the

basics of arrays and the syntax rules

let's do some practical examples so

prepared a project we can do for this

lesson we'll go to our browser create a

new tab at the

top and here we'll type

superimple

dodev SL projects slash arrays and press

enter so this page contains the to-do

list project we're going to create in

this lesson so down here is the final

version of the project we can type a

name for our to-do like make

dinner give it a due date and then click

add and it will add it to our list we

can add another to-do like wash

dishes and then select a due date and

click add again and it will add another

to-do to our list and each to-do also

has a delete button so we can delete it

when we're finished the task so this is

the final version of the project and

these two up here are simpler versions

of the project that we're going to use

to work our way up so let's start with

the first project up here we're going to

open our console by

right-clicking click

inspect and click the

console and the way way this first

project works is we can type a to-do in

this text box like make

dinner and when we click add it will add

the to-do to an array and display it in

the

console if we type another to-do like

wash dishes and click add it will add it

to the array and display it in the

console so let's create create this

project we'll start by creating a file

for this project we'll go to our code

editor and click up here to show our

files and click this icon to create a

file and we'll name this

11-

too-

list.

HTML and press

enter now let's copy the code from

arrays and loops. HTML

so we'll click here control a or command

a and then

rightclick

copy and down here right click and

paste and let's close this for

now we'll scroll up and change the title

to to do list and remove all the

JavaScript code

and this time instead of writing all the

JavaScript in here let's actually put

the JavaScript in a separate file which

we learned in the previous lesson so

we'll open our files

again and this time we'll go to our

scripts folder we'll click this JS file

and we'll click this icon to add a new

file to this folder and let's name it

11- to-do Das

list.js and press

enter next we're going to load this file

into our HTML file so let's open this

and in the script element we can remove

the spaces and we're going to add an

attribute called

SRC equals and we're going to load the

Javascript file that we just created

which is inside the script folder so

we'll type

scripts and then a slash to go into this

folder and we'll load the file

11-

too-

list.js and

save so now I'm going to drag this file

down here so I can see both the HTML and

JavaScript at the same time close this

for now and I can close the other code

for now as

well and finally let's open this in our

browser so we'll right

click open with live

server and let's also open the console

on this page right click click

inspect and click the

console now one more thing I'm going to

do for this video is I'll rearrange my

windows so that we can have the the

final design at the

bottom let's start by creating the HTML

elements let's go to the body and we'll

actually create a paragraph element to

start inside the paragraph we'll put the

text to-do

list next let's create the text box so

to create a text box less than

input greater than and add a placeholder

to this text box Place holder equals to

do name finally let's add this

button so on a new line let's type less

than button greater than and inside the

button we'll have the text

add now let's

save and this creates all the HTML

elements that we need

next let's write our JavaScript so first

we're going to create an array to store

our to-dos and then when we click the

add button we're going to get the text

from the text box and add it to our

array and finally we'll console.log the

array now let's convert these steps into

code let's create a new array first

using const

let's name it

to-do list and we'll make it equal to

square

brackets so this is an array with no

values inside we also call this an empty

array next when we click the button

let's get the value from the text box so

let's go to our button and add an

onclick

attribute and then inside here let's

create a function for this so down here

let's create a

function we'll name it add Todo brackets

and curly

brackets and then inside the onclick

attribute we're just going to call this

function add too and

brackets the next step is to get the

text in the text box we can do that

using document. query selector so to use

Query selector we're going to put a

class on this input element so we'll

type the class

attribute

js- name Das

input and then in here document do query

selector brackets and a string and we'll

type a DOT to get a class and we'll get

this class

js-

name-

input as a reminder this gets an element

with the class JS name input which is

this element and puts it into our

JavaScript and now let's save this in a

variable so at the start let's type

const in input element and make it equal

to this

result so now we took this input and put

it into our

JavaScript to get the text out we're

going to use a property of the input

element called value so down here

input

element.

value and let's save the value in the

text box in a variable so we can use it

later

at the front const name and we'll make

it equal to whatever's in the text

box before we continue let's

console.log the name to check if this is

working so let's save this Javascript

file and let's also save this HTML

file we'll go to our browser and I'll

resize it so we can you can see the

console and now if we type something in

the text box like make dinner and click

add it will get the text from the text

box and then display it in the

console okay so it's looking good so far

the next step is to add this name to our

to-do list so we learned how to do this

earlier we can use a method called push

push will add a value to the end of the

array so let's remove this for now and

at the

bottom we're going to type our

array to do

list. push

brackets and then between the brackets

we're going to add our name

here and now the last step is to

console.log the entire array

console.log Todo

list and

save now let's give it a try or'll type

make dinner in the text box and click

add it will take this text add it to the

array and then console.log the array and

now we have our to-do list let's add

another to-do we'll type type wash

dishes and click

add again it will get the text in the

text box and then add it to the array so

now our array has two values and then we

display them in the

console so that's how we create this

first version of the to-do list project

now one more feature we're going to

create is if we add something to our

to-do list and click add

it will reset the text box to do that

let's go into our

code and we'll create some new lines and

remember that the value property

represents the text in the text box so

to change the text in the text box we

can simply change the value property so

we'll type

input

element. value and change it to the

empty string

so this will make the text in the text

box become empty if we

save and now type something in the text

box and click

add it will reset the text in the text

box let's move on to the second version

of the to-do list so here when we type

something in the text box like make

dinner and click add it will actually

display it on the page if we type

something else like wash dishes and

click add it will also add it to the

page so how do we take our array and

display each value on the page to do

this we're going to learn another

feature of JavaScript called loops loops

let us run some code over and over like

a loop so let's go back to our 11 arrays

and Loops file and we can close this

JavaScript file for now and we're going

to learn Loops so first let's comment

out the previous code by typing

slashstar and at the bottom star

slash let's scroll

down and we'll create our first Loop

we'll start by creating a variable using

the word let and we'll name name this

variable I and we'll make it equal to

1 next we're going to type the word

while and then brackets and curly

brackets and then inside these curly

brackets we're going to put some code

that the computer will run over and over

just like a loop let's put the code

console.

log

I so this will display the variable I in

the console over and over again now

obviously we don't want to Loop this

forever so how do we get this Loop to

stop we can do that using the round

brackets up here inside these round

brackets we're going to put some code

that results in true or false for

example we can check if I is less than

or equal to 5 so the way this works is

that if this code results in true the

loop will keep going over and over once

this results in false the loop will stop

and it will go to the next line now you

may notice that this code will never

result in false because I is equal to 1

and 1 is always less than or equal to 5

so when does this actually become false

and Stop the Loop the answer is inside

this loop we're also going to update

this variable I so we'll type I and

we'll make it equal to itself plus

1 so now every time we Loop over this

code we're going to increase I by 1 and

eventually I will be greater than 5 this

will return false and it will stop the

loop if we

save and then go back back to the tab

for this file and I'll rearrange my

windows so we can see the console this

Loop makes the computer count from 1 to

5 so let's go over this code step by

step to make sure we understand how it

works first we create a variable I and

we make it equal to one and then we do a

loop so if this condition is true the

computer will keep running this code

over and over again so the first time it

Loops I equals 1 and then it displays

one in the console and then we increase

I to two now we go back to the top and

we check this code 2 is less than or

equal to 5 this is true so we're going

to run this code again this time I equal

2 and we display it in the console and

then we we increase I to three and now 3

is still less than or equal to 5 so this

is true which means we keep running this

code and eventually this is going to

increase I to six once I is six this

will become false which will cause the

loop to stop and then we go to the next

line so that's why it counts from 1 to 5

and then it stops at five

so this is called a while loop while

this condition is true it will keep

running this code over and over again

just like a loop as soon as this

condition is false it will stop the

loop all right now that we understand

how a while loop Works let's learn the

syntax rules to create a while loop we

type the word while and then round

brackets and curly brackets the code

inside the round brackets is called the

loop condition the code inside the curly

brackets is called the loop body the

variable I at the top is called the loop

variable every time we loop we're going

to increase the loop variable this is

known as the increment step the

increment step makes sure that the loop

ends at some point without this

increment step the loop would just keep

going forever this is known as an

infinite

Loop now remember that I = I + 1 has a

shortcut instead of this we can just do

I plus = 1 and remember we actually have

an even shorter shortcut for plus equal

1 instead of this we can also do I ++

so this will increase the value of I by

one every time just like before so those

are the three major parts of a loop the

loop variable the loop condition and the

increment

step now each time we run this Loop this

is called an

iteration so in this Loop we did five

iterations we ran this code five times

and lastly Loops create a scope any

variable that we create between these

curly brackets will only exist inside

the curly brackets so that's a while

loop while this condition is true it

will keep running this code over and

over again once this condition becomes

false it will stop the loop and go to

the next

line so in JavaScript there's actually

two types of loops

the first type is a while loop which we

just learned now we're going to learn

another type of loop called a for Loop

to create a for Loop we'll create some

new lines and then down here we'll type

four and brackets and curly

brackets inside these brackets we're

going to type three pieces of code the

first piece of code is a loop variable

which is the same thing as this line up

here so we'll type let I equal one and

then semicolon space and we'll type a

second piece of code which is the loop

condition so here we'll type I less than

equal to 5 and then semicolon and space

and the last piece of code is the

increment step which is this line right

here so we'll type

i++ and between these curly brackets

we'll write the code that we want to

Loop over and over so let's just type

the code

console.log I and

save so this for Loop does the same

thing as the while loop above it counts

from 1 to 5 and if we look at this code

we can see that a for Loop is just a

shorter version of this while loop

instead of writing the loop variable

condition and increment step separately

we group all of them together at the top

so this Loop works the same way first we

create a loop variable and then as long

as this Loop condition is true we will

keep running this code over and over and

every time we run this code we're also

going to increase the loop variable by

one so now that we learned two ways of

doing a loop which one should we use if

we're doing a standard Loop for example

it has a loop variable a condition and

an increment step every time it's

recommended to use a for Loop because a

for Loop is shorter and more organized

than a while loop however if it's a

nonstandard loop then it might be better

to use a while loop so what's an example

of a non-standard loop so let's say we

want to Generate random numbers until we

get a number that's at least

0.5 to create this Loop we'll create a

variable that will store the random

number using

let

random

number and make it equal to zero to

start and then we'll do a while

loop brackets and curly brackets now

inside the loop condition we want to

keep running this Loop until random

number is at least

0.5 so we'll check if

random number is less than

0.5 because if it is less than 0.5 we

want to keep running this Loop until we

get a random number that's at least

0.5 and then inside this loop we're

going to generate a random number

between 0 and 1 and then save it in the

variable up here so we'll type random

number and make it equal to capital M

math.

random so if this random number is less

than 0.5 it will keep generating random

numbers until we get a number that is at

least

0.5 so at the bottom if we

console. log

random

[Music]

number and

save it will give us a random number

that's at least

0.5 so notice that this is a

non-standard loop it doesn't really have

a loop variable that we increase every

time and it also doesn't have the

increment step so in this situation when

we have a non-standard loop it's better

to use a while loop because they're a

bit more

flexible all right now that we learned

the basics of Loops let's do some

practical examples we're going to learn

a technique called looping through an

array this means we're going to go

through each value of an array one by

one and do something with each each

value so first let's comment out the

previous code using

slashstar and star slash at the bottom

let's create an array of strings so

we'll create a variable const to do list

equal to an

array and inside this array we'll have

the string make

dinner another string wash

dishes and another

string watch

YouTube now let's take each value in

this array and display it in the console

to do that we're going to run a loop and

this Loop is going to count from zero to

the last index in the array so remember

that the index is the position of a

value in the array the first value is

index zero the second value is index one

third value is index 2 and so on So

Below this let's type four brackets and

curly

brackets inside these brackets we're

going to create the loop variable so

here we're going to count the

indexes let index equals zero semicolon

space and we'll do the loop condition so

we'll keep looping as long as the index

is less than or equal to the last index

so remember that the index starts from

zero this means that the last index in

an array will be the number of values in

the array minus one or the array. length

minus

one to do list do

length minus

1 and here we'll add another semicolon

and we'll add the increment step which

is index Plus+ so we'll increase it by

one every time now inside these curly

brackets we can do something for each

index of this array for now let's just

console. log this index

and

save so this will count from 0 to two

which is exactly all the indexes in this

array and now using this index we can

also access the value at this

index so instead of just the index here

we can do to-do list and then square

brackets and between the brackets index

this will take whatever the index

variable is and access that index in the

array so if the index variable is zero

this will access to-do list index0 which

is the first value when the index is one

it will access to-do list index one

which is the second value and so

on so for now let's save the value in a

variable using const value

and make it equal to to-do list bracket

index and now let's

console.log the value instead if we

save this will Loop through each index

of the array get the value at each index

and then display each value which is

what we see in the console so this

technique is called looping through an

array we use a loop to go through each

value of an array and then we can do

something with each

value now I'm going to show you a few

shortcuts we can use when looping

through an array instead of checking if

index is less than or equal to to-do

list. length minus one we can shorten

this to index less than to-do list.

length so this check does the same thing

as before the loop Loop will stop at

index equal length minus one but it

saves us some

typing another shortcut is instead of

naming the loop variable index we can

shorten this to

I and we'll shorten this as well and

this as well and that's why we often

name the loop variable I I means

index next we're going to learn a

technique that we can combine with

looping through an array called the

accumulator pattern so first let's

comment out the previous code using

slashstar and star

slash and at the

bottom let's say we have an array of

numbers like this how do we calculate

the total of all the numbers in the

array let's set up this problem let's

say we have an array of numbers const

nums equals array and then the numbers 1

1 and

3 and we want to calculate the total of

all the numbers in this array to

calculate the total we'll learn the

accumulator pattern the first step of

the accumulator pattern is to create a

variable to store the result so below

this let's create a variable const total

and we'll make it equal to zero and the

next step is to Loop through this array

and update the result so down here four

brackets and curly brackets and inside

the round brackets we'll create the loop

variable let I or index equals z

semicolon space and we'll create the

loop condition I less than nums do

length and then semicolon and the

increment step

i++ so as we learned earlier this Loop

will go through each index of this array

and now between these curly

brackets first let's use the index to

get each value so we'll type

nums and then square brackets and access

the index I and let's save this in a

variable using

const num equals this

value and finally we're going to add

each number to the total we can type

total and make it equal to

itself plus each number and remember

remember we have a shortcut for this

which is plus

equals and finally since we're changing

this total variable we have to change

from const to

let all right so after this Loop we

should have added each number in the

array to the total so at the bottom

let's

console. log the

total and Save

and it will display five which is the

exact total of all the numbers in this

array so that's the accumulator pattern

we first create a variable to store the

result and then we Loop through the

array and update the result so notice

that as we Loop through the array we're

adding or accumulating the results into

this variable and that's why this is

called the accumulator pattern pattern

and we call this variable the

accumulator

variable all right let's do another

example using the accumulator pattern

let's say we're given this array of

numbers again and we want to create a

copy of the array where each number is

doubled so if the array is 1 13 we're

going to create a new array with 2

26 so as at the bottom we'll create some

new lines and use the accumulator

pattern the first step is to create a

variable to store the result let's type

const and let's name this

nums

doubled and we'll make it equal to an

array this time so notice in the

previous example the accumulator

variable was a number in this example

the accumulator variable is an array so

we can use different types of values to

accumulate the result it all depends on

the problem we're trying to solve so now

the next step is to Loop through this

array and update the result at the

bottom we'll create a four Loop brackets

and curly

brackets inside the round brackets we'll

create the loop variable let I equal

zero and we'll create the loop condition

I less than nums do length and then the

increment step

i++ and now between the curly brackets

we're going to get the number at each

index so const num equals nums square

bracket I and then we're going to update

the result

so down here we're going to add this

number doubled to this

array so remember to add a value to an

array we can use the method push so

we'll type

nums

doubled do push

brackets and we're going to add to this

array the number num multiplied by 2 and

now at the bottom

let's

console. log the result nums

doubled and

save so this second Loop will create an

array where each number is doubled so

that's how we solve this

example all right now that we understand

how to Loop through an array and the

accumulator pattern let's go

back and we'll create the second version

of our to-do list so when we add

something to the list it will appear on

the page let's go to our code editor and

we'll open 11 Todo list.

HTML and we're also going to open the

Javascript file so it's this one and for

the video I'm going to drag it to the

bottom of my code editor so that I can

see the files side by side so I'll close

this for now

and I'll rearrange my windows a

bit let's open the tab for this project

so we'll review what we have so far we

can click in this text box and type a

to-do like make dinner and click add and

it will add this to-do to this array

which is this array right here we can

type another to-do like wash dishes and

click add and it will add it to the end

of the array so now that we have this

array of to-dos we want to display it on

the page to do that we're going to Loop

through this array and we're going to

create some HTML code for each to-do and

then put that code on the web page using

the Dom so first let's Loop through this

array to make this easier let's make a

copy of this array so right click

copy and then here we'll remove this and

rightclick and

paste so this will give us some default

values to work with so at the top let's

Loop through this array using a for Loop

so we'll type four brackets and curly

brackets and then in inside the round

brackets we're going to create the loop

variable let I or index equal zero

semicolon and the loop condition I less

than too list do

length semicolon and then the increment

step

i++ so this will Loop through each index

of this array and then inside the curly

brackets let's get the string for each

index so we'll create a variable to save

it const to-do and we'll make it equal

to to-do list square brackets and

I and now for each to-do we're going to

create some HTML code so we'll create a

new line and create a variable const

HTML and make it equal and we'll create

some HTML code using this to-do using a

template

string and then inside we'll create a

paragraph element so less than P greater

than and then less than SL P greater

than inside this paragraph we're going

to insert this to-do so we'll type

dollar and curly brackets and

Todo all right so now we're looping

through this array and for each to-do we

created some HTML code and now we're

going to combine all of this HTML code

together and put it on the web page to

combine this HTML together we're going

to use the accumulator pattern so at the

top of the loop we'll create a variable

to store the result let to do list

Capital

HTML and we'll make it equal to the

empty string at the start and then as we

Loop through the array we're going to

add this HTML to the variable up here so

let's create a new line and we'll do

to-do list Capital

HTML plus equals

HTML to combine all of this HTML code

together so now after the loop let's

console do log to do list

HTML to see what we get if we

save we took this array of strings

generated paragraph elements for each

string and then combine them all

together so now that we have all this

HTML we can put it on the page using the

Dom so first let's create an element

where we can put this

HTML so inside the HTML file after the

button we're going to create a different

type of element called a div element so

we'll type less than div greater

than so the div element represents a

container its purpose is to contain

other elements inside like paragraphs

buttons and even other

divs so in this situation we can't

actually use a paragraph element because

in HTML we cannot have a paragraph

inside another paragraph so that's why

we have to use a div element here for

now let's put some text inside this

element so we can learn more about it

we'll type text and Save

so like the paragraph element the div

element is a block element that means it

will take up an entire line by itself

and that's why it appears below the text

box and the button now one difference

between a div and a paragraph is that a

paragraph adds extra space above and

below the paragraph while a div does not

add any extra space above or below so it

doesn't have any default

styling all right so now that we learned

the div let's put this HTML code inside

this div first we need to get this

element into our JavaScript and to do

that we'll add a class to this element

class equals

js- too Das

list and then down here let's scroll

down and we'll put this div element

inside our JavaScript we can do that

using document do query

selector brackets and a string and we'll

type a DOT to select a class and we'll

select the class

js-

too-

list so this will get this div element

and put it in inside our

JavaScript and then every HTML element

has a property called dot inner Capital

HTML which controls the HTML inside this

element and now to put the to-do list

HTML into this div element we're going

to make the inner

HTML equal to the

to-do list HTML

and now let's save this

file and also save the HTML

file so this code will take the HTML

that we created using the loop and put

it into the div element and that's how

we make them show up on the page so now

let's try adding another to-do we'll

type watch YouTube and click

add and unfortunately

this new Todo doesn't show up on the

page and that's because when we click

add it will run this add Todo function

and update the list but we didn't

actually update the HTML on the

page so to update the HTML we need to

run all this code again every time we

add a too so let's create a function for

this code so we can reuse it so at the

top we'll create a

function and let's name this

render

to-do list brackets and curly

brackets so the word render means to

display something on the page so we'll

put all of this code into this function

so we can delete this curly bracket and

then at the end we'll type a closed

curly bracket and let's reformat this

code by selecting these lines and then

press tab to add an

indent so now let's use this function at

the start we'll display this to-do list

on the page so we'll call this function

by typing render

to-do list and

brackets and then let's scroll down

every time we add a to-do to the list

we're also going to display the list

again so at the bottom

render to do list and brackets again so

if we

save at the start it will display the

list on the page and then if we add it

to the list like watch YouTube and click

add it will add it to the list and also

display it on the page so that's how we

create the second version of the to-do

list

project by the way if we scroll up to

the render Todo list function this

technique is called generating the

HTML instead of writing all the HTML by

hand up here we looped through an array

and we generated the HTML using

JavaScript

so when creating websites with

JavaScript we usually follow a

three-step process first we save the

data in this case we saved our data as

an

array next we use the data to generate

the HTML which we did here and finally

we make the website interactive which

we'll do later in this

lesson this is the main idea of

JavaScript and we follow follow this

overall process when creating

websites the rock paper scissors project

from the previous lessons was a bit

different because all the HTML we needed

was already there we just had to modify

it with

JavaScript so this process we're using

for the to-do list is one step above

what we did for rock paper scissors we

need to generate some

HTML and this is a standard process for

creating websites we're going to use

this process for the to-do list and

later the Amazon Project as well as

websites that you build Beyond this

course let's take a break before

continuing with the rest of this lesson

here are some exercises that will help

you practice what we learned so far

now let's create the final version of

the to-do list we'll go back to

superimple

dodev and then here we'll scroll down

and we'll create this final version so

in this version we can type a too like

make

dinner and we can also add a due

date and when we click add each to-do

will now have a name and a due date and

they will also have a delete button that

we can click to remove it from the list

so let's build this out one feature at a

time we'll start by creating this delete

button we'll go into our code and

remember we're generating the HTML

for the to-do list so for each value in

the array we create a paragraph element

so to add a delete button we just have

to add a delete button inside here so

inside the paragraph we'll create a less

than button greater than and then less

than SLB button greater than and then

inside this button we'll put the text

delete

let's

save and in the console you'll see that

the HTML we generated now has a delete

button inside the paragraph and that's

what shows up on the

page next we're going to reformat this

HTML to make it a little easier to read

so we'll create some new lines here and

at the

end and let's put the content of the

paragraph on its own line like this

and also put the delete button on its

own line so remember that template

strings have a feature called multi-line

strings so this is perfect for writing

HTML

code the last step in the process is to

make the website

interactive so next let's make our

delete button do something when we click

it to do that we use the onclick

attribute as usual so inside this button

we're going to add an

onclick attribute equals double quotes

and then inside these double quotes we

can run some JavaScript when we click

this button so this works the exact same

way as what we've been doing so far in

this course the only difference now is

that here we're generating this HTML

using

JavaScript okay so when we click one of

these delete buttons we want to remove

this to-do from the list earlier in this

lesson we learned how to remove a value

from an array using a method called

splice so inside this onclick attribute

we're going to type the to-do list dot

splice and

brackets so splice takes two numbers the

first number is the index that we want

to remove

so if we click this delete button how do

we know which index to

remove well if we look at our Loop up

here we already have the index it's this

variable I so we're going to insert I

into this string and we can do that by

typing dollar curly brackets and

I now splice also takes another number

so we'll type comma and the second

number is how many values we want to

remove so here we just want to remove

one value at this

index and finally because we updated the

to-do list we need to display the list

again on the page to display the list we

can use this function render to do list

so down here we're going to type render

Todo list and brackets

now if we

save you can see that in the generated

HTML when we click the first delete

button it will remove the value at

index0 which is the first value if we

click the second button it will remove

the value at index one which is the

second value so we're basically

generating all this HTML using a loop so

now if we click this delete button

it will remove it from the list and then

display the updated list on the page so

that's how we create the delete

button next let's go back to superimple

dodev and we're going to create the due

date

feature so first let's create this date

selector in our

HTML we'll go to our HTML file and then

under the text box we're going to add

another input element

so less than input greater than and to

make it a date selector input elements

have an attribute called

type so this attribute determines what

kind of input it is if the type is text

which is the default value it's going to

be a

textbox now if we change the type to

date and

save it's going to create a date

selector now let's go back into our

JavaScript code and first we're going to

scroll up and remember that right now

our to-do list is just an array of

strings but this time each to-do is also

going to have a due date so how do we

group the name and the due date together

we can do that using an object so here

instead of just a string we're going to

create an an object and we'll give it a

name property which is make dinner and

we'll give it a due date property and

we'll make the due date a

string so you can type whatever date you

have on the page for me it's 20

22-12

d22 and I'll end this object with a

curly bracket and I'll turn this to do

into an object as well so open curly

bracket

name and do

date

2022

D12

d22 and closed curly

bracket now that each to-do is an object

we need to update the rest of our code

let's scroll down and we'll start with

the render function

so here inside the loop each to-do is no

longer just a string it's an object so

let's change this variable name to to-do

object to make it more clear and now we

need to get the name and due date out of

this object so we'll type const name

equals to do object. name and const do

date equals to do

object. do

date and now instead of inserting to-do

which no longer exists we're going to

insert the

name and we're also going to insert the

DU

date if we

save now each to-do will also display a

due

date before before we continue we're

going to review a shortcut we can use

with objects called

destructuring so here you'll notice the

variable name is the same as the

property name we actually have a

shortcut for this using

const curly brackets

name equals Todo

object so this is called destructuring

this takes the name property out of the

object and and puts it in a variable

also called name and this is a shortcut

for this line up here so we can comment

out this line we can also use multiple

properties in this shortcut to also take

the due date out of the object we can

just add a comma and do

date so this will do the same thing as

this line of code and we can comment

this

out if we save

everything still

works next let's scroll down and we're

going to update our add Todo function so

this time when we click the add button

we're going to get the name and the due

date and put it into our list so let's

get the due date out of this date

selector first we can do that using the

Dom like we did here so let's add a

class attribute so we can get it using

queries selector

js- do

dd-

input and then down here let's create a

variable

const date input element and make it

equal to

document. query

selector and a string Dot and then the

class we want to select which which is

this class

js-

do-

date-

input so this will get the date selector

element and put it into our

JavaScript and now below this let's get

the due date out of the

element we can do that using the value

property again so let's create a

variable first const do date and we'll

make it equal to the date input

element.

value so this will get the date that we

selected and save it in this

variable and now when we add a to-do to

our list instead of just a name we're

going to add an object so open curly

bracket We'll add a name property and

the value will be the name variable up

here so name and then comma and a doe

date

property and the value will be this due

date variable up here so due date and

then a closed curly

bracket and remember that objects also

have a shortcut for this if the property

and the variable name are the same we

can just type it out once like

this this will do the same thing as this

line above same thing with the second

line if the property and the variable

name are the same we can just type a

comma and type it out

once this is called the shorthand

property syntax so these two lines do

the same thing as these lines above so

we can comment this out using double

slash and double

slash so that's all the code that we

needed to update now let's save our

Javascript

file and we'll also save our HTML

file and let's go to our project We'll

add a new to-do like watch

YouTube and select a

date and click

add and scroll down you can see that it

added our new to-do with a name due date

and a delete button

if we click this delete button it will

remove that to-do if we click this one

it will also remove the correct

to-do and that's actually all the

functionality that we need for this

project so let's go into our code and

we're going to clean up by removing the

console.log

here and the console.log up

here and Save

finally let's add CSS to our project to

make it look like the final design we'll

go into our code editor and scroll to

the top and instead of writing all the

CSS in here let's put the CSS in a

separate file just like our JavaScript

so we'll click here to show our

files and then find the Styles folder

and we'll click the Styles folder and

click this icon to create a new file

inside and we'll name this file

11-

[Music]

to-do-list

docss and press

enter and for the video I'm going to

take this CSS file and put it at the

bottom of my code editor so I can see

these files side by side and now I'll

click here to close

it and will load this CSS into our

HTML to do that we can use a link

element so inside the head section let's

type less than link greater than and

we're going to give it two attributes

Rel equals style

sheet and

hre equals the file that we want to load

so we created this this in the Styles

folder so we'll type Styles and then a

slash to go into the folder and we load

this file

11-

too- list.

CSS and

save now let's style our project one by

one until it matches the final design

we'll start with the text on the page

we're going to change the font so in

here let's type

body curly brackets and then we'll

change the font Das family colon Arial

and

save so that looks pretty good now let's

work on styling the to-do list first

let's add some more to-dos to the list

so we'll type

watch

YouTube and then we'll select a date

and click

add and we're going to learn how to

style our list to look like this so

notice that this list creates a sort of

grid we're going to create this grid

using a feature called CSS grid so let's

go into our HTML

first we're going to add a class to this

div element so we can style

it to-do Das grid R and let's

save and inside our CSS we're going to

style this class using dot Todo Das grid

and curly

brackets and to turn this into a grid

we're going to use the property

display and

grid and we're going to add another

property called grid Das template Dash

columns so this basically sets how many

columns are in our grid the number of

values that we give it is the number of

columns for example if we give it 200

pixels 150 pixels and 100

pixels this will create three columns in

the grid the First Column will be 200

pixels the second Colum column will be

150 pixels and the third column will be

100

pixels and now each element inside this

div will go into the columns so the

first element will go in the First

Column second element will go in the

second column and the third element will

go in the third column if we have more

than three elements it will wrap around

and create a new

row so let's

save and and unfortunately that didn't

quite work and that's because if we go

back to our

JavaScript remember that each to-do is

one paragraph element so this entire

to-do with the name due date and delete

button will go inside the First Column

and then the next entire to-do will go

inside the second column but what we

actually want is for the name to go in

column 1 due date column 2

and delete button column 3 to do this

we're going to separate this element

into three elements so that each element

will go into each

column so instead of one

paragraph let's actually use a div

element so less than div greater than

and less than slash div greater than and

in between we'll insert the name

so the reason we use a div element is

because div elements don't have any

default styling so it's a little easier

to style with

CSS for the due date let's also create a

div element so less than

div and then at the end less than slash

div greater than and finally for the

delete button we already have an element

so so let's just reformat these lines

we'll select these lines and then press

shift tab to remove the

indent let's remove the extra line and

we basically separated each to-do into

three

elements if we

save now the grid is working because

this element goes into the First Column

this element goes into the second column

and the button goes into the third

column

and that's how we lay out these elements

in a grid like the final design next

let's also lay out the inputs and the

add button in a grid we'll go to our

HTML and let's put these three elements

in a div so we can use grid so we'll

create a less than div greater

than and then

inside let's remove this and we'll add

it at the end less than SL div and let's

reformat these lines by selecting them

and then press tab to add an

indent and now let's make this div a

grid as well let's go back to our CSS

and we'll add a class to this div class

equals let's call it to-do Das input d

dgrid and instead of writing all this

CSS again we can use a feature of CSS so

here we're going to type a comma and

enter so when we type a comma we can

style multiple classes at the same time

so we're also going to style dot

too- input Das grid if we save the CSS

file

and let's also save the HTML

file now the input and the add button

are also laid out in the same

grid next let's adjust the spacing

inside our grid so grid has some

properties for this we'll go to our CSS

press enter and we'll use the property

column Das Gap so this sets the spacing

between the Columns of the grid so let's

make this colon 10 pixels and

save so now it will add 10 pixels

between each column let's add some

spacing between the rows as well and

grid has another property for this row

Das Gap colon 10 pixels and

save so that will add 10 pixels of space

between the rows now notice it didn't

add space between these two rows and

that's because these two are separate

grids this is the to-do list and this is

the to-do input

grid so to add space between them we

just going to use

margin at the bottom we'll style dot

too- input Das

grid and we'll just add some margin

under this grid so margin Das bottom

colon 10 pixels and

save all right now let's move on to

styling the inputs and the buttons we'll

start with the inputs first let's add a

class so we can style them here let's

add a class name Das

input and down here let's let's also add

another class

do- dat Das

input let's

save and now inside our CSS we'll style

both of these

inputs so we'll style do

name- input curly brackets and first

let's make the text bigger like the

final design we'll set the font Das size

colon 15 pixels and save okay so that

looks pretty good now let's add spacing

on the inside of this input so we'll add

padding six pixels and

save and that looks pretty good let's

move on to the due date input so we

actually want the same Styles as the

name input so again we can use that

feature of CSS we'll type a comma and

then dot

do-

date- input so now these Styles will be

applied to this class and to this class

let's

save and that looks pretty good to me

let's move on and style the

buttons we'll go into our HTML and find

the add button let's add a class so we

can style

it and we'll use add-

too- button let's

save and then inside our CSS we'll style

that class using dot add-

too- button curly

brackets and let's start with the

background color we'll set the

background-color

colon

green and

save now let's do the text

color color colon

white and

save now let's remove the border around

our button using border colon

none

save and let's make the text a little

bigger so we'll do font

D size colon 15

pixels and

save and the last thing we'll add is

when we put our Mouse over the button it

turns into this pointer icon we can do

that using

cursor colon

pointer and

save next let's style the delete buttons

so these delete buttons are created in

our JavaScript we'll go into our

JavaScript

file and then here let's add a class to

each of the delete buttons so we can

style them so we'll add class equals

double quotes and then delete Das

too-

button let's

save and then inside our

CSS at the bottom we style dot delete

Das too Das button curly

brackets and let's start with the

background color so we'll set background

Das color colon and for this design I

use the color dark

red and

save so that will style our delete

buttons now let's change change the text

color to white so we'll use color colon

white and

save now let's remove the Border using

border colon

none

save and let's also make the text bigger

using font Das size colon 15

pixels save

let's add this pointer icon using cursor

colon

pointer save and let's add some padding

at the top and bottom of the button so

we'll add

padding-top colon 10 pixels and padding

Dash bottom colon 10 pixels and Save

so that's all the Styles we need for the

delete button and we can also close the

console to see the entire list however

now we have another problem which is

this text and this button are not

vertically aligned in the center to

vertically align in the center we're

going to go back to the grid Styles so

we'll scroll

up to the to-do

grid and CSS grid has another property

for vertical alignment and that is align

Das items Colon

Center to vertically align in the center

if we

save now the text is aligned with the

button but now we have a new problem our

add button is no longer stretching to be

the same as the inputs so by default

align items is

stretch that's why this button stretches

to match the inputs and now that we

changed it to align center it's no

longer going to stretch so to solve this

problem we just have to make this grid

stretch so down here in the to-do input

grid Styles we'll change align Das items

back to

stretch and Save

save and that will cause this Grid at

the top to stretch vertically again and

that's it that's all the styling that we

need and now we finished this to-do list

project in the rest of this lesson we're

going to learn more details about arrays

and

Loops so I'm going to put this back in

the same

window and I'll rearrange this

window and now let's go back to 11

arrays and loops.

HTML and we'll open the tab for that

file and we can also close these other

files for

now and first let's comment out the

previous code

using

slashstar and at the bottom star

slash and we'll scroll down and

save the first detail we're going to

learn is that that arrays are references

so in the object lesson we learned that

objects are references arrays work the

same way so for example if we create an

array

const array 1 equals the array 1 2

3 this variable doesn't actually contain

the values 1 2 3 this array is saved

somewhere in the computer's memory and

this variable only contains a reference

that points to where this array is in

memory and that means if we create a

copy of this variable

const array 2 equals array

1 array 2 doesn't contain a copy of the

values it actually just contains a copy

of the reference so now both of these

variables are pointing to the same array

so if we did array

2. push

for and then we

console.log array 1 and we

console.log array

two and

save it will show us that even though we

added four to array two array 1 and two

were both modified and that's because

arrays are references so both of these

point to the same array in memory to

avoid this Behavior we can create a copy

of the values in the array using a

method called slice so here if we did

array

1. slice instead

this will make a copy of the values in

Array one and now these two variables

point to two different arrays if we

save now you'll see that this line only

affected array

two the second detail we're going to

learn is a shortcut called

destructuring so at the bottom here

let's create a new array

const array 3 3 equals the array 1 2

3 and let's say we want to get the first

value and the second value out of this

array one way to do this is to use the

index like this another way is to use a

shortcut called

destructuring so here we're going to

replace this with square brackets and

now we can type some variable name

if we type first value it will take the

first value and save it in a variable

called first value if we type comma and

second value it will take the second

value and save it in this variable so

this is an easier way to get values out

of an array and save them inside a

variable next we're going to learn more

details about loops so Loops have two

features called break and continue break

lets us exit a loop early for example

let's create some new lines and let's

create a loop that counts from 1 to 10

so as usual we can use a four

Loop let I =

1 I less than or equal to 10

and I

++ and we'll

console. log I and

save so this will count from 1 to

10 so now let's say that when I is 8 we

want to stop this Loop early so first

let's check if I is equal to 8

if it is equal to 8 we're going to stop

this Loop by typing break and

semicolon if we

save once this reaches eight break will

cause this Loop to stop and now it only

counts up to eight so that's the break

feature of a loop it lets us stop a loop

early the next feature is called

continue continue lets us skip one

iteration of the loop or one run of the

loop for example let's say we want to

skip the number three so at the top we

can check if I is equal to

three and if it is we can use the code

continue this will skip the rest of this

code and go back up to the top of the

loop and do i = 4 if we

save this will skip three in the loop so

continue let us Skip One iteration of

the loop so now let's say that we want

to skip a number if it's divisible by

three divisible by three means the

number can be divided evenly into three

for example 3 and six are both divisible

by three but s is not divisible by three

because there's one remaining this is

called the remainder and we can

calculate the remainder using the

remainder operator which looks like this

so to check if a number is divisible by

three we can check if the remainder is

zero so here we're going to replace this

with I remainder 3 and we'll check if

the remainder is equal to to Z if we

save this will skip three and six

because they're both divisible by

three next let's use continue in a while

loop so at the end here we'll create

some new lines and let's say we want to

count from 1 to 10 using a while loop so

we'll create a loop variable let I equal

1 and we'll create a while

loop I less than or equal to 10 curly

brackets and the increment step

i++ and inside the loop we just

console. log I and

save so this will count from 1 to 10

again and let's say we want to not count

numbers that are divisible by three so 3

6 and 9 so at the top here we can check

if I remainder 3 is equal to zero and

curly brackets and we might just try to

do

continue however in a while loop

continue will actually skip the

increment step and this will cause an

infinite Loop Loop so when using

continue in a while loop we have to do

this increment step manually so before

continue we have to do I

++ to avoid an infinite Loop if we

save it will skip the numbers that are

divisible by three which is 3 6 and 9 so

remember in a while loop if we use

continue always do the increment step

manually in a for Loop however the

increment step is done automatically

after every

iteration all right the last detail

we're going to learn is how to use loops

with functions so let's say we have an

array of numbers and we want to create a

copy of this array where each number is

doubled so we already have the code for

this we can scroll up and the code for

this is here

so let's actually make a copy of this

code from before we'll

rightclick

copy and scroll down

here and at the

bottom right click and

paste at the top let's create an array

called

nums so const nums equals array and one

1 and

three if we

save this will create an array where

each number is

doubled now what if we wanted to use

this loop on a different array other

than one one and three we can do that

using a function so let's create a

function around this Loop we'll create

function let's name it dou full

array brackets and curly bracket we'll

remove the closed curly bracket and at

the bottom We'll add it back and we'll

select these

lines and press

tab so now instead of doing this loop on

the same array every time we can turn

this into a parameter so at the top here

we'll create a parameter called

nums and we're going to delete this

line and we're going to Loop over this

parameter instead so at the bottom we

can call our function using double array

and

brackets and between the brackets we're

going to save an array into nums so

square bracket 1 1 and 3 if we

save this will do the same thing as

before but now because it's in a

function we can use this loop with any

array not just one one and three so at

the end we can do double array

brackets and an array 2 2 five this time

and

save and it will create an array where

these numbers are doubled so using a

function we can reuse this Loop for any

value another feature of using a

function with a loop is that we can

break out of this Loop using a return

instead so first let's actually use a

return in this function instead of

console.log we're going to

return nums doubled

and here we're going to console.log the

result

console.log and

console.log and

save so this does the same thing as

before except we're returning the result

and console. logging outside of the

function now let's say that if we see

the number zero we want to stop this

Loop early to do that we can click here

and check if num is equal to

zero and if it is we can break out of

this Loop now when we're inside a

function we can also use a return

statement to break out of this Loop so

we can also do return nums

doubled so a return statement will end

this function immediately so this is

another way of ending the

loop so down here if we add the number

zero and then five and

save you'll notice that the loop stops

when we see the number zero so return is

another way of breaking out of a loop

when it's inside a function and that's

the end of this lesson in this lesson we

learned about arrays which represent a

list of values we learned about loops

which let us run some code over and over

just like a loop we learned a Technique

we can use with loops called the

accumulator pattern and we used it to

create a to-do list project we learned

that arrays are references and the

destructuring shortcut and we learned

more features of Loops like break

continue and using Loops inside a

function here are some exercises to help

you practice arrays and loops

in this lesson we're going to learn some

Advanced features of functions and we're

going to use them to improve our

previous

projects first let's create a new file

for this lesson we'll go to our code

editor and click here to show our files

and click here to create a new file and

we'll name this

12- Advanced D

functions.

HTML and press

enter now let's copy 11 arrays and Loops

into this file so we'll click here

control a or command a and then

rightclick

copy and in

here right click and paste

and we can close this for now and let's

prepare this file for this lesson so

we'll scroll

up and change the title to

Advanced

functions and let's remove all the

JavaScript code from

before and now let's save and open this

file in the browser by right click

clicking open with live

server and let's also open the console

on this page so we'll

rightclick

inspect and open the

console and now we can close the

previous

tabs as well as the previous

files and now we're ready to begin so

first we're going to review how to use

fun

functions inside the script element

let's create a function using the word

function will give it a name

greeting brackets and curly brackets and

inside the function we'll type the code

console.log the string

hello so this is a function and it lets

us reuse code to run the code inside

this function we can type the function

name which is greeing and then

brackets if we

save this line of code we'll run the

code inside the function and display

hello this is known as calling the

function or running the

function so now that we understand

functions we're going to learn an

advanced feature of functions which is

functions are values so we learned many

types of values in this course like

numbers strings and booleans and we can

save a value in a variable for example

let's create some new lines and we'll

create a variable const num equal

2 so this will save the value two inside

the variable num

now functions are also values and this

means just like a number we can save a

function inside a variable so let's give

it a try we'll create a new line and

type

const function one and we'll make this

equal to a function this time so we'll

just type

function and a name

greeting brackets and curly

brackets and inside the function we'll

type

console. log the string hello

2 and we'll put a semicolon at the end

since we're saving in a

variable so this variable now contains a

function we're using the exact same

syntax as before except we're just

taking this function and saving it in a

variable because functions are values

so now that this function is inside this

variable let's actually console.log it

so we

console.log function one and

save and this will show us that the

variable function one actually contains

this

function now on a new line we can also

do console.log

and check the type of function one and

save and it will tell us that the type

of this variable is a function so as you

can see a function is just another type

of value and we can save it in a

variable we can also run the function

inside this

variable by typing the variable name

function 1 and because this contains a

function we can actually just call it

using

brackets so this will run the code

inside this function if we save it

displays hello

to now let's do some Cleanup in this

code in JavaScript as long as there's a

way to access a function this function

name is not needed so here we can access

this function using this variable so

this function name is not needed and we

can actually just delete it like this

and now this is called an anonymous

function which means a function without

a

name now an interesting thing to know is

that the function syntax that we've been

using this entire course up here is

actually a shortcut for this code now

even though this syntax uses VAR and we

usually don't recommend VAR this syntax

actually has a couple advantages number

one it's easier to read and number two

it gives us a feature called hoisting

which means we can call this function

greeting brackets before we create it in

the code so using hoisting we don't have

to worry about what order we write this

code hoisting doesn't work when we

create our function and save it in a

variable like this so in JavaScript

functions are values and just like any

other value we can save it in a

variable now let's think what else can

we do with a value well we can save a

value in an object for example let's

scroll

down and create some new lines and we'll

create an object

const object 1 equals curly

brackets and inside this object we'll

have a property num with the value

two so this saves the number two inside

this object now because functions are

values we can also save a function

inside this object so we'll type comma

and then a property fun colon and we'll

create a function this time function

[Music]

greeting brackets and curly brackets and

inside we type

console. log the string hello

3 so this saves a function inside this

object under the property fun now to

access this function we just use the dot

notation as normal so object one dot

fun and because this value is a function

we can call it using

brackets if we

save this will run the code inside the

function and display hello 3 so remember

this is called a method when we have a

function saved inside an

object again as long as there's a way to

access this function for example using

object one. fun then we don't need this

function name so we'll delete it and use

an anonymous

function now let's think what else can

we do with a value we can pass a value

into a function for example down here

let's create a function

function

display brackets and curly brackets and

we'll give this function a parameter so

in here we'll create a parameter and

name it

param and inside the function we can use

a parameter just like a variable so we

console.log the

param and then down here let's call this

function using

display brackets and two

this will take the value two save it

inside Pam and then we can use it just

like a variable if we

save this will display two in the

console so this is known as passing a

value into a function now because

functions are values we can also pass a

function into a function so let's give

it a try down here

we'll create a new function

function run brackets and curly

brackets and this function will also

have a parameter let's call it

param and down here we'll call this

function run

brackets and between the brackets we're

going to give it a function this time so

we'll type function

brackets and curly brackets and inside

the function we'll type

console.log the string hello

4 so this will take this function and

save it inside Pam and now up here we

can use Pam just like a variable so we

can type

Pam and because Pam contains a function

we can actually just call it using

brackets if we

save this code will run the function

that we created down here and display

hello 4 so this is called passing a

function into another

function the function that we're passing

in is called a callback function or a

callback so to summarize functions are

values anything we can do with a value

we can also do with a

function now let's do some practical

examples using functions as values we're

going to learn a feature of JavaScript

called set timeout set timeout allows us

to run a function in the

future first we'll comment out the

previous code using

slashstar and at the bottom

star slash and let's create some new

lines and we're going to type the code

set capital T time

out so set timeout is a built-in

function so we can type brackets to call

this function Now set timeout takes two

parameters inside these brackets the

first parameter is a function that we

want to run in the future

let's create a

function brackets and curly brackets and

inside this function let's type

console.log the string time

out so here we're using a function as a

value and we're passing it into another

function at the end we'll type a comma

and we'll give set timeout a second

parameter the second parameter is how

long to wait before running this

function so this is a number in

milliseconds 1,000 milliseconds is equal

to 1 second so if we type 3,000

milliseconds this is equal to 3 seconds

so set timeout will wait for 3 seconds

and then call this function if we

save after 3 seconds

it's going to display timeout in the

console so that's set timeout we give it

a function and it will call this

function after a certain amount of

time so now we're going to learn an

important concept called a synchronous

code so after set timeout let's type

console.log the string next

line and Save

so notice that it displays next line

first and then after 3 seconds it

displays timeout so what's happening

here why are they reversed set timeout

sets up a timer and after 3 seconds it

will call this function however it

doesn't actually wait for the 3 seconds

to finish it just sets up the timer and

immediately goes to the next line so

that's why this line is displayed first

so this is called asynchronous code

asynchronous code means the computer

won't wait for this line to finish

before going on to the next line so for

set timeout it'll just set up the timer

and then immediately go to the next line

synchronous code on the other hand means

the computer will wait for one line to

finish before going to the next line so

all the code we've written in this

course so far has been synchronous code

in addition all the code inside this

function is also synchronous code so if

we added

console.log the string time out

to and

save the code inside the function will

still run line by line it will wait for

each line to finish before going to the

next line and after 3 seconds it will

display timeout followed by timeout

2 so don't worry all the code that we

normally write will be synchronous code

it will run line by line as usual the

only time that code becomes asynchronous

is when we use certain features of

JavaScript like set timeout so set

timeout is the only part that is

asynchronous now the advantage of set

timeout being asynchronous is that it

does doesn't block our code for 3

seconds waiting for this timer to finish

it just sets up the timer in the

background and then goes to the next

line of code so this allows our code to

do other things while this timer is

running in the background and this is

similar to real life if you set up a

timer on your alarm clock you're not

going to stop and wait for the timer to

finish you're going to go and do

something else asynchronous code is the

exact same concept

next we're going to learn a similar

function to set timeout called set

interval so at the bottom let's type the

code set capital I

interval and set interval is another

built-in function so we can call it

using

brackets and set interval takes these

same two parameters as set timeout the

first parameter is a function that we

want to run in the future so let's type

function brackets and curly brackets and

inside we'll type

console. log the string

interval now let's add a comma and the

second parameter is also a number in

milliseconds so we'll type 3,000

milliseconds or 3 seconds so set

interval will run this function 3

seconds in the future but this time it

will keep running the function every 3

seconds if we

save in the console every 3 seconds it

will run the function and display

interval so set interval is also

asynchronous below it if we type

console.log the string next

line

two and

save it will set up the interval and

then immediately go to the next line and

display next line two so that's set

interval we give it a function and it

will keep running this function after a

certain period of time so now let's do a

project using what we learned so far

let's go to our browser and we'll create

a new tab at the top

top and here let's type

superimple

dodev slash projects slash Advanced Das

functions and press

enter so this is basically the rock

paper scissors game that we created

earlier except this time it has an extra

button called autop playay if we click

this Buton

button every second the computer will

play by

itself so this feature will help us

practice using set

interval so first let's make a copy of

the project files we'll go into our code

editor and click this icon to show our

files and let's make a copy of 10 rock

paper scissors for this lesson so we'll

rightclick copy

and down here rightclick and

paste and I'll stop this for now so here

we're going to change the name by right

clicking

rename we'll remove copy at the end and

at the beginning we'll change it to 12

and press

enter and let's also make a copy of the

JavaScript and CSS files so we'll click

this file and right click

copy and then click the folder right

click

paste and we'll rename this file

rightclick

rename remove copy at the end and at the

beginning change it to 12 and press

enter and let's also make a copy of the

CSS file select it rightclick copy

click the folder right click and

paste and right click

rename remove copy and at the front

change it to 12 and press

enter now let's scroll down to 12 rock

paper

scissors and I'll close this for

now and inside the head let's change

this to load 12 rock paper scissors and

we'll scroll to the

bottom and here instead of the lesson 10

file we'll load The Lesson 12 Javascript

file let's save and we'll open this in

the browser by

right-clicking open with live

server so now we're ready to begin let's

go back to superimple

dodev and the first thing thing we're

going to create is this autoplay button

so beside the reset score button which

is here we're going to create a new

button less than button greater than and

inside we'll have the text auto

play let's

save and go back to our

Tab and now we have this button so next

let's style this button with CSS so

we'll give it a

class class equals

auto-play Das

button and

save and now let's open the CSS

file I'm going to take this file and

then drag it to the bottom so I can see

it side by side so I'll close this for

now and rearrange this a little bit and

then down here and we're going to style

the autop playay button so let's just

make the style the same as the reset

score button so in the CSS we'll scroll

down to the reset score button Styles so

we'll add a comma at the end and type

dot

auto-play dasb button so now these

Styles will apply to the class reset

score button and the auto playay button

if if we

save now we styled our project so next

let's make this button interactive so at

the top here we'll add an onclick

attribute and then in here we're going

to run some JavaScript code let's

actually create a function so we can

separate the JavaScript into its own

file so we'll run a function called auto

play and

brackets so now let's

save and right now this function doesn't

exist so we have to create this function

in the Javascript file so for me the

file is right here I'll select it and

then drag it down here so I can see it

side by side so let's scroll down and

I'm going to create it just above the

play game function so here we'll create

some new lines and type function

auto play brackets and curly

brackets and now inside this function we

want to play the game every second so we

can use set interval to run some code

every second so let's type set

interval

brackets and inside the brackets will

give it a function that we want to run

so brackets and curly

brackets and then at the end let's type

a comma and we'll give it

1,000 so this means it will run this

function every 1,000 milliseconds or 1

second and now inside this function

we're going to automatically play the

game and to play the game we can use

this function right here play game so

here we'll type play game

brackets now we need to provide this

function with a Player move and remember

we have another function pick computer

move which will give us a random move so

above this line let's create a variable

const

Player move and we'll make it equal and

we'll pick a random move using pick

computer move

and

brackets and finally we'll take this

move that we picked and pass it into

this function so Player

move so now when we click this button it

should play the game every second let's

save and click

autoplay and it works the computer is

playing against itself every second so

now let's make this button button stop

playing when we click it again so at the

top let's create a variable to keep

track of whether or not we're playing so

we use let is auto playing and at the

start we'll make it equal to

false and

save and now inside this function we'll

check using an if statement brackets and

curly

brackets and inside this condition let's

check if we're not playing so not is

auto

playing so if we're not playing then we

want to start playing the game which is

this code down here so let's select this

code and then right click

cut and in here right click and

paste and also after we start playing

the game we're going to change this

variable to true so is auto playing and

we'll make it equal to true because now

we are autop playing so now let's add

the else Branch to this

statement else curly

brackets so now we need to stop this

interval so how do we do that the answer

is that set interval actually returns a

number and this number is like an ID we

can use this ID to stop the interval so

at the front let's create a variable to

save this ID

const

interval ID and

equals however there's another problem

here every time we run the function

we're going to get a different ID so in

order to save the ID from last time we

need to put this variable outside the

function so let's select this and remove

it for now and we'll scroll up and here

we'll create the variable let

interval ID and we'll leave it undefined

to start and now down here we're going

to save the return value into this

variable by typing

interval ID equals set

interval and now at the bottom we're

going to use the interval ID to stop the

interval let's scroll down and to stop

an interval we can use a function called

clear interval so we'll type clear

capital I interval

and

brackets and between the brackets we're

going to give it an ID that we want to

stop so we'll give it this interval

ID

interval

ID and then at the bottom let's also

change is autop playing to false because

we just stopped it so is auto playing

equals false

and

save so now if we try out this

button it will start playing the game by

itself every second and if we click the

button again it will stop playing the

game so that's how we stop an interval

we need to save the ID and then call

clear interval with this ID so now I'll

clean up the code a little by removing

this extra line and Save

and now we're finished with this

feature so next let's go back to our

Advanced functions file so I'll click up

here and then at the bottom I'll open 12

Advanced

functions and hide the files for now and

we're going to learn some more features

of functions as values so let's actually

close the other files that we opened

and first let's comment out the previous

code with

slashstar and at the bottom star

slash let's scroll down and

save and let's open the tab for this

file so now we're going to learn another

way to Loop through an array first let's

create an array we'll type square

brackets and inside the array we'll have

the string make

dinner and another string wash

dishes and another

string watch

YouTube so in the previous lesson we

learned how to Loop through an array

using a for Loop or a while loop another

way to Loop through an array is using a

method of the array called four each so

at the bottom let's type dot for capital

E each and

brackets so this is the four each method

and it allows us to Loop through this

array inside these brackets we're going

to give for each a function so we'll

type

function brackets and curly brackets so

again we're just passing a function into

another

function however this function will be a

little different we're going to give it

a parameter so up here let's create a

parameter called

value so what four each does is that it

Loops through the array and for each of

these values it will save the value in

the parameter and run the function so

let's

console.log

value and

save so this will Loop through the array

and display each value in the console so

let's go through this step bystep so

it'll take the first value save it in

this parameter and run the function then

it will take the second value save it in

the parameter and run the function then

it will take the Third value save it in

the parameter and run the

function so the for each method is

actually the preferred way to Loop

through an array because this is easier

to read than a for Loop like this and

for each also has another feature we can

give this function a second parameter so

we can type comma and the second

parameter is the

index or the position of the value in

the array so for the first value index

will be zero for the second value index

will be one third value index will be

two and so on so above this line let's

also

console.log the

index and

save and this will also display the

index of each

value all right now let's do a practical

example using the for each method we're

going to go back to the to-do list

project that we created in the previous

lesson so we'll click up here to show

our

files and let's scroll up and let's open

11 too

list.js so in this code we used a for

Loop to display the to-do list on the

page we're going to switch this to using

a for each method instead said so first

let's actually make a copy of the files

for this project we'll click up

here and let's click 11 to-do list and

rightclick

copy and let's click the script

folder rightclick and

paste and now we'll rename this by

right-clicking

rename remove copy from the end and

change the beginning to 12 and press

enter let's also make a copy of the CSS

and HTML file for this project so we'll

click the CSS file right click

copy click the Styles folder right click

and

paste rightclick

rename remove copy

and at the front change it to 12 and

press

enter and finally we'll scroll down

click 11 Todo list.

HTML

rightclick

copy and then down here right click and

paste right click

rename remove copy at the end and at the

beginning change it to 12 and and press

enter now we can hide these

files and we can close the lesson 11

files and now here we're going to change

the CSS file that we load to 12 to-do

list and we'll scroll down and we'll

also change the Javascript file that we

load to 12 to-do list now let's

save and we'll open this in the browser

by right clicking

open with live

server okay now let's go back to the JS

file so I'll take this file and drag it

to the

bottom and I'll rearrange the windows

here we're going to scroll down and

we'll change this for Loop to use a for

each method so first let's type above

this for Loop and we'll type the array

that we want to Loop through which is

Todo list and we'll type Dot and use the

four each method and

brackets inside the brackets we'll give

it a function that we want to run for

each to do so we'll type

function brackets and curly

brackets and this function can have two

parameters the first parameter will

contain each value in the array so we'll

call it too

[Music]

object we'll type a comma and the second

parameter contains each index in the

array so we'll just call it

index and now inside this Loop we

basically want to do everything that we

did here so let's just make a copy of

this

code right click

copy and then up here inside for each

right click and and

paste so now if we scroll up we already

have the to-do object up here so we

don't need to get it from the array like

before so we can remove this line and

let's also remove these

comments the other thing we have to

change is that previously we were using

I for the index but now the index is

called index so we just change this to

to

index so that's how we use a for each

method instead of a for Loop if we

compare this code to the four Loop that

we had before the for each method is

easier to read so for the rest of this

course we're going to prefer to use four

each instead of a for Loop so we're

going to remove this for

Loop let's scroll back up and

save and the project still works so

that's a practical example of using the

for each method now let's go back and

learn some more details about for each

we'll close the Javascript file for now

and go back to Advanced functions. HTML

and open the tab for this

file so in the previous lesson we

learned a feature of Loops called

continue continue lets us skip to the

next iteration or the next run of the

loop for each methods don't have

continue but we can do the same thing

with a return statement so let's say in

this Loop we don't like washing dishes

if the value is wash dishes we're going

to skip it and not display it in the

console so above we'll create an if

statement

and then inside the condition we'll

check if value is equal to the string

wash

dishes and then in the curly brackets if

it is equal will return and

semicolon so this return statement will

end this function early and it will go

on to the next function so it basically

does the same thing as continue in a for

Loop if we

save you'll notice that it skipped wash

dishes in the previous lesson we also

learned a feature of Loops called break

break lets us exit a loop early

unfortunately there's not an easy way to

break in a 4 each Loop so if we need to

use break to exit this Loop early then

it's better to use a regular for

Loop let's take a break before

continuing with the rest of this lesson

here are some exercises that will help

you practice what we learned so far

so next we're going to move on and learn

a shorter way to write functions called

Arrow functions so let's go to the

bottom of this code we'll create some

new lines and let's create a variable

const and we'll name the variable Arrow

function and we'll make it equal to to

brackets equal greater than or an arrow

and then curly

brackets inside the curly brackets we'll

type some code

console.log brackets and the string

hello and we'll put a semicolon at the

end so this is an arrow function it

works the same way as a regular function

for example we can call this Arrow

function by typing the variable name

Arrow

function and

brackets if we

save this line of code will run the code

inside this Arrow function and display

hello so Arrow functions mostly work the

same way as regular functions so to

compare them let's actually type above

this code we'll create some new lines

and type

const

regular

function equals the word

function brackets and curly brackets

console.log string

hello so these two syntaxes do the same

thing the difference is that instead of

using the word function an arrow

function just uses an

arrow now parameters work the same way

in an arrow function we just type the

parameter between these round brackets

so here let's type

param and here as

well if we want multiple parameters it

also works the same way up here we can

type comma param 2 and down here comma

Pam 2 and finally return statements also

work the same way so in this function we

can return five and in the arrow

function we can also return

five so now let's learn some differences

between these two Arrow functions have a

few shortcuts that regular functions

don't have for example at the bottom

let's create an arrow function using

const and we'll name it one

perm and make it equal to an arrow

function brackets arrow and curly

brackets now in this Arrow function

we're going to give it one parameter

param and inside the function will

console.log param plus

one so when an arrow function only has

one parameter these round brackets are

optional so we can actually remove

them if we do one param brackets 2 if we

save it will display 2 + 1 which is

3 let's learn another shortcut we'll

create some new lines and type const one

line and make it equal to an arrow

function brackets arrow and curly

brackets and inside will return 2 +

3 so when an arrow function only has one

line like this we can actually put it on

the same line as the

arrow and now that everything's on the

same line the curly brackets are

actually optional so we can remove them

and we can also remove the return

statement so this is a oneline arrow

function if we just have an arrow it

will automatically return the result on

the right so at the bottom we can

console. log and call the one line

function with

brackets if we

save this function will return to plus

three and it will display five in the

console so that's Arrow functions it's a

shorter way of writing a regular

function and it has a few

shortcuts for now let's get some

practice using Arrow functions so let's

scroll up in this code to the for each

method so let's use an arrow function

here instead we just have to remove the

word

function and after the round brackets

add an arrow equals greater than if we

save the loop still works so when we're

passing a function into another function

like for each it's recommended to use

Arrow functions because it makes our

code easier to read so now let's use use

Arrow functions in some of our previous

projects we'll start with the rock paper

scissors game let's open our files by

clicking

here and we'll find the 12 rock paper

scissors. JS

file and then inside this file we're

going to scroll down to the autoplay

function so here we're passing a

function into another function so it's

recommended to use an arrow

function let's remove the word

function and add an arrow so now this

code is a little easier to read now what

about this function up here function

autoplay should we also switch this to

an arrow function so this situation is

more personal preference so above this

let's actually create an arrow function

version of this const

auto play equals brackets and arrow and

curly

brackets so even though we could create

an arrow function version of this I

actually prefer the regular function

syntax here for two reasons number one I

think this is easier to read than this

and number two this function syntax

enables hoisting which means we can call

this function before we create it and we

don't have to worry about which order we

write the code so for these reasons I

actually prefer this situation to use a

regular function syntax and not an arrow

function so we'll comment out the arrow

function using double

slash and double

slash now let's

save and let's open the tab for this

project and we'll give give it a try so

click

autoplay and this still works after

replacing with an arrow

function next let's go to the to-do list

project and switch to Arrow functions so

we'll go to our code editor and find the

to-do list project which is

here and let's scroll

down so inside render to-do list we're

using four each and we're passing this

function into another function so it's

recommended to use an arrow function

here so we'll remove the word

function and after the brackets We'll

add an

arrow and again I'll leave this function

syntax as a regular function because

it's easier to read and enables hoisting

so let's

save and go back to our to-do list

and everything still

works next let's go back to 12 Advanced

functions.

HTML and we'll scroll to the

bottom and we'll open the tab for this

file and we'll review another place we

could use Arrow functions which is

inside an object so at the bottom here

let's create a new object con

object 2 equals

object and then inside let's type the

property method colon and an arrow

function brackets arrow and curly

brackets so even though we could save an

arrow function inside an object like

this objects already have a shortcut for

functions so at the bottom we could just

type

method brackets and curly

brackets so this syntax is called the

shorthand method syntax so this

shorthand method syntax is actually

easier to read than an arrow function so

when saving a function in an object it's

actually recommended to use this syntax

instead there's also another difference

between regular functions and arrow

functions but we'll learn about it later

in in this course because it's a more

advanced

feature now let's move on and we're

going to learn another Improvement we

can make to our projects so let's

comment out this code we'll scroll up

and type SL star and at the

bottom star slash and

save and next we're actually going to

scroll up to the very top of this file

and we're going to create a button on

the page so inside the body we'll type

less than button greater than and inside

the button we'll have the text

click now let's say that we want to run

some JavaScript code when we click this

button so here we can type on click

equals double quotes and write some

JavaScript inside this double quotes

quot now we're going to learn a better

way of doing this called add event

listener to use add event listener first

we're going to get this button and put

it into our JavaScript using document.

query selector so let's add a class to

this button so we can select it and

we'll set it to

js-

button and now inside the script element

we're going to use

document. query

selector brackets and the string do

js-

button so now let's save this button in

a variable so we can use it later at the

front we'll type

const button element equals this

result now every HT H ml element has a

method called add event listener add

event listener let us run some code when

we interact with the element so it sort

of does the same thing as

onclick so at the bottom let's type

button

element dot add capital E Event capital

L

listener and brackets

so add event listener has two parameters

the first parameter is the event or what

type of interaction we want to listen

for so between these brackets let's type

the string

click so this will run some code when we

click the button the way to find these

event names is to look at this attribute

the word after on is the

event next the second parameter is a

function that we want to run when we

click this element so we'll type a comma

and because we're passing a function

into another function we're going to use

an arrow function so we'll type

brackets arrow and curly

brackets so inside here let's just do

console. log string click

and

save and now when we click this button

it will run this function and display

click so this code does the same thing

as the onclick attribute however add

event listener has some advantages over

using an attribute first it lets us add

multiple event listeners for an event

for example let's add another click

event listener we can select this

code and

rightclick

copy and then down

here rightclick and

paste and let's change this to log click

to if we

save and click the

button it will run both these functions

so add event listener let us add

multiple listeners to one event another

advantage of doing this is that we can

remove an event listener using a method

called remove event

listener so under this code we can type

button

element do remove capital E Event

capital L listener and

brackets and remove EV listener also has

two

parameters the first parameter is the

event so in this case it is the string

click and we'll type a comma and the

second parameter is the function that we

want to remove so that when we click

this button it will no longer run that

function now we can't just type a copy

of this function we need to use this

exact function inside remove event

listener to do that we'll save this in a

variable first so above this let's

create a

variable

const event

listener equals and we'll select this

code right click

copy and in here right click and

paste and now we'll replace this with

the VAR

variable event

listener and down here we'll remove this

same

variable event

listener if we

save and click the button again it will

only display click two because we added

this event listener and then we removed

it so it will no longer run this

function when we click the button so as

you can see

add event listener gives us more control

over event listeners we can add multiple

listeners to an event and we can also

remove a listener from an event so

because of these advantages the best

practice is to use add event listener

instead of an onclick attribute so let's

go back into our projects and switch to

using add event listener we'll start

with the rock paper scissors project so

we'll open our

files and we'll open 12 rock paper

scissors and click here and

save and we'll scroll up to 12 rockpaper

scissors. JS and for the video I'll drag

this down to the bottom and I'll hide

the files for

now and then rearrange the

windows and finally open the tab for

this file

now let's go to the HTML we'll scroll up

to these move buttons which is up

here so here we're using the onclick

attribute and we're going to switch it

to add event listener so first let's get

this button into our

JavaScript We'll add a class so we can

select it

js-

rock- button

and

save and then down

here let's go below the autoplay

function right here and we'll use add

event listener so we'll get this button

into our JavaScript using

document do query

selector brackets and a string dot

js-

ro-

button and we're going to use dot add

event

listener

brackets so we're going to listen for a

click and a comma and we'll give it a

function that we want to run so a common

mistake here is to actually run the

function for example play game brackets

and the string

Rock so we're supposed to give a

function to add event listener however

this doesn't result in a function this

will actually run play game and give us

the return value which is undefined so

this code will actually result in

undefined and then we're giving

undefined to add event listener so it

won't

work so in order to give add event

listener a function we need to create a

function here

so let's remove this code and we'll

create a function using brackets arrow

and curly

brackets and then inside this function

we're going to call play game so we'll

type play game brackets and

rock so now when we click the rock

button it will run this function and

play the game so let's remove the

onclick

attribute and save the

HTML and also save the

JavaScript and then go to our project

and click the rock button you can see

that it works except this time we're

using add event listener so let's do the

same thing for the paper and the

scissors button feel free to pause the

video if you want to try it

yourself so we'll scroll down here and

let's add a class to the paper button so

we can select it

js-

paper- button and then in our JavaScript

we'll make a copy of this code so right

click

copy and then down

here right click and

paste and now we're going to replace the

rock button

with

paper and when we click this button

we're going to play the game with

paper now let's

save and we'll remove the onclick

attribute and save the

HTML if we click the paper button it

works as

before finally let's do the scissors

button so we'll add a class Js

s- scissors dasb

button and then inside our JavaScript

we'll make a copy of this rightclick

copy and then down here create some new

lines rightclick and

paste and now switch to the scissors

button and play game with

scissors let's save

and remove the onclick

attribute save the

HTML and try the scissors

button so everything still

works and I'll leave switching the reset

score button and the autop playay button

as

exercises so now let's try add event

listener with a different event we'll

use it with key down so let's say that

in our project we want to make it so we

can play the the game with our keyboard

if we Type R it will play Rock if we

type P it will play paper and if we Type

S it will play

scissors let's go into our

JavaScript and we'll scroll

down and we're going to add an event

listener to the body this time so that

if we type anywhere on the page we can

run some code so we're going to get the

body element using document

body and

then add event listener and

brackets this time the first parameter

or the event will be the string key

down and let's type comma and give it a

function that we want to run brackets

arrow and curly

brackets inside here let's just type

console.log key down for now and

save so now if we go to the project and

we open the console

rightclick and click

inspect click the

console and then click on the page if we

type a key on our

keyboard it will run this function and

display key down so now we have to check

what key was pressed and play the game

so how do we know which key that we

pressed earlier in this course we used

the attribute on key down and we learned

that it gets a special object called

event and the event object contains

which key was pressed add event listener

also provides this event object but it

provides it as a parameter to this

function so inside the round brackets

let's add a parameter

event now every time we type on our

keyboard add event listener will save

the event object in here and run the

function and this event object contains

the key that we

pressed so in the console.log let's

display event. key this time and

save now if we click on the page and

type R

event. key will contain R if we press P

event. key will contain P so that's how

we know which key we pressed so now

let's close this and instead of

console.log we'll create an if statement

to check which key we pressed so if

brackets and curly

brackets and here we'll check if event.

key

is equal to the string R if it is we're

going to play the game with rock so

inside here we can just run this play

game

function play game and brackets and

inside we'll type the string

Rock now let's check if we pressed P so

we'll add another Branch else if

brackets and curly brackets and in the

second condition we'll check if event.

key is equal to the string P if it is

we'll play the game with paper so inside

here we'll run play game brackets and

the string paper and finally we'll check

if we pressed s so at the end We'll add

another else if brackets curly brackets

and inside here we'll check if event.

key is equal to the string s if it is

we'll play the

game with the string

scissors now let's

save click our page and type R

and it plays the game with rock if we

type P it will play the game with paper

and if we Type S it will play the game

with

scissors so that's an example of using

add event listener with a different type

of event with a key down if we need the

event object we can get it using a

parameter up here so those are all the

features we're going to create for our

rock paper scissors project

now let's move on to the to-do list

project and switch to add event listener

we'll go into our code editor click up

here and find 12 to-do list.

HTML we'll also scroll up to the scripts

folder find 12 to-do

list.js and open this file and I'm going

to put it at the bottom here so I can

see it side by side I'll close this for

now

and close rock paper

scissors and then open the tab for this

project okay so let's start by switching

the add button to use add event listener

we'll go into our HTML and find the add

button which is here and we're going to

add a class so we can select it in

JavaScript

js-

add- too dasb button

now let's go to our JavaScript and

scroll

down above the add Todo

function we'll get this button into our

JavaScript using

document. query

selector brackets and then a string Dot

and the class we want to get

js- add- too dasb button

and then after this we use do add event

listener

brackets inside these brackets we'll

give it the event the string click comma

and then a function to run when this

event happens so brackets arrow and

curly

brackets and in here we just want to do

the same thing as the onclick attribute

which is ADD too and call this function

let's

save and then in the HTML let's remove

the onclick

attribute and

save and let's try it out so we'll type

A

too watch

YouTube select a due

date and then click add

and the add button still works as before

but we're just using add event

listener next let's switch all the

delete buttons let's scroll up to where

we create these delete buttons which is

here and first We'll add a class to all

the delete buttons so we can select them

in

JavaScript

js- delete Das too dasb button

and now we're going to use document.

Query selector and add an event listener

to all of these buttons however there's

two problems here first is that at this

point in the code this is just a string

we haven't actually put this button on

the page yet we do that down here in

this line of code we put the HTML that

we generated onto the page so in order

to add an event listener we need to put

the HTML on the page first so we have to

do it after this code so down here we're

going to type

document. query

selector brackets and the string Dot and

we'll select this class

js- delete Das too

Dutton however there's also a second

problem here which is we're going to

have multiple delete

buttons and query selector only gives us

the first one so how do we select all

the buttons on the page that match this

criteria instead of just the first one

to do that the document object has

another method called query

selector

all so query selector all will give us

all the elements on the page that have

the class JS delete Todo button so down

here let's console.log this result to

see what it looks like

[Music]

console.log brackets and close bracket

and

save and then here

rightclick

inspect and the

console and expand this you'll see that

document. query selector all gives us a

list of elements and this list works

just like an array this is index zero or

the first button and this is index one

which is the second button so now let's

remove

console.log and add event listeners to

all of these

buttons to do that we're going to Loop

through this list of delete buttons

so again this list works like an array

so we can use a for each method to Loop

through it so at the end let's type

enter and tab and then dot for each and

brackets as usual we'll give for each a

function that we want to run for each of

these values so we'll type brackets

Arrow and curly

brackets and now every time we Loop

through the list for each will give us

two parameters the first one is the

value in the list which is a delete

button element so let's name it delete

button and we'll type comma and the

second parameter is the index so

index so now we want to add an event

listener to each delete button so inside

here we'll type delete button dot add

event listener and

brackets inside these brackets we'll

tell it what event we want to listen to

which is the string click and comma and

then a function that we want to run when

this event happens so brackets Arrow and

curly

brackets so now when we click a delete

button we want to do the same thing as

this onclick attribute above so let's

select this

code we'll

rightclick

copy and then down

here right click and

paste and now we can remove these

characters because we're not in a string

anymore and that's all we need to

do so to summarize we used query

selector all to get a list of all the

delete buttons on the page and then we

looped through the list using four each

and for each delete button we added a

click event listener and ran the same

code that we did before so now we can

scroll up and remove this onclick

attribute and Save

go back to the page close a console and

try out the delete

button and you can see that it still

works so that's how we switch the to-do

list project to use add event

listener so now we're finished improving

all of our

projects in the rest of this lesson

we're going to learn more features that

use functions as

values so let's close this for now and

we'll go back to

12 Advanced functions.

HTML and we'll open the tab for this

file and let's also comment out this

JavaScript code using

slashstar and star

slash let's

save and now let's scroll to the bottom

of this

code and create some new

lines so in this lesson we learned the

array method for each which lets us Loop

through an array now we're going to

learn two more array methods called

filter and map so let's start with

Filter let's say we have an array of

numbers and we want to create a copy of

this array with all the negative numbers

removed so let's go up here and create

an array of the number one comma -3

comma 5 and type the method do

filter and

brackets so Filter Works the same way as

for each we give it a function so

bracket arrow and curly bracket and this

function has two parameters the

value and the

index so filter will take the first

first value save it in here and run the

function then it will take the second

value save it in here run the function

and the third value save it and run the

function now the only difference is that

this time this inner function will

return a value so we'll type

return and we're going to return a

Boolean like

true so now the return value matters so

what filter does is it creates a new

array if the inner function returns true

it will put this value in the new array

if the inner function returns false it

will not put this value in the new array

for example at the front let's

console.log the result of this so we'll

type

console.log Open Bracket and down here

close bracket and Save

so in this example the inner function

always returns true so all three values

will be in the new array if we change

the return value to false every time and

save all three values will not be added

to the new

array so now let's use this to solve our

problem we want to remove the negative

numbers from this array so inside this

inner function we're going to return

true if the number is positive and

return false if the number is

negative so we'll check if value is

greater than or equal to

zero curly brackets will return true and

include it in the new

array

else will return false and not include

it in the new array so let's remove this

and

save so now only values that are greater

than zero will be in the new copy so

using this we can sort of filter out

values based on a criteria that's why

this method is called

filter now we can shorten this logic by

using this code return value greater

than or equal to zero so this comparison

will return true if it's greater than or

equal to zero and it will return false

otherwise so this line does the same

thing as this code up here so we can

comment this out with slashstar and star

slash and

save and as always we can return a

truthy or falsy value instead of just

true or

false the last array method we're going

to learn is called map so let's create

some new lines and scroll

down and let's say we have an array of

numbers again like the array 1 1 3 and

we want to make a copy of this array

with each number

doubled so at the end we'll

type map

brackets and Map works just like for

each and filter between the brackets

we'll give it a function bracket arrow

and curly brackets and this function

will get two

parameters the first parameter is each

value in the array and the second

parameter comma is the

index so map will take the first value

save it in this parameter and run the

function take the second value

save it in this parameter run the

function third value save it and run the

function and inside this function we're

going to return a

value so what map does is it creates a

new array and then whatever we return

will be added to the new array so if we

return

10 and then we console.log this result

console.log

and close bracket and

save it will create an array where each

value becomes

10 now the interesting thing is that we

can actually use the value itself in the

return so here if we did value + 10 and

save it will take each value in the

original array add a 10 and put it in

the new array

so map will transform an array into

another array based on the return value

so if we want to return an array where

each number is doubled we just have to

multiply each value by two and save and

this will give us 2

26 next we're going to review some

shortcuts of Arrow functions to make

this code more

compact first let's make a copy of this

code rightclick

copy and down

here rightclick and

paste so notice in the inner function

we're not using index so let's just

remove it for now and now that this

Arrow function only has one parameter

these round brackets are optional so we

can also remove these to make the code

more compact another shortcut is if we

only have one line of code in an arrow

function we can put the code on one line

like

this and now the curly brackets and the

return are optional so we can actually

just remove all of this

code so if we have just an arrow it will

automatically return this result on the

right and we don't have to type return

ourselves

so this code does the same thing as the

code above but as you can see these

shortcuts make our code very Compact and

clean so let's save and this will give

us the same

result the last thing we're going to

learn in this lesson is a feature of

functions called a closure a closure

means if a function has access to a

value it will always have access to that

value so let's take a look at an example

we're going to go back to the to-do list

project so we'll click up here and then

scroll up to 12 to-do

list.js and close this and then open the

tab for the to-do list which is here and

let's scroll down to the query selector

all so we're going to focus on this

inner function here so notice that this

fun function uses index from above now

the interesting thing about index is

that as soon as this for each ends index

gets deleted for example if we add some

new lines and we try to

console.

log

index and

save and then go into our project

rightclick

inspect and the con

it'll tell us that the index is not

defined so as soon as we end the for

each Loop index doesn't exist

anymore however if we move this into the

inner function so inside here and we

console.log

index and

save and we click a delete button it

will tell us that the index is zero so

even though index gets deleted right

away down here if we click one of these

buttons later on it still has access to

Index this feature is called a closure

if a function has access to a value it

will always have access to that value

the value like index gets packaged

together or enclosed with the function

that's why we call it a closure

so even if the value index gets deleted

after the loop we can click the delete

button 5 seconds later or even 5 minutes

later and this function will always have

access to

index so closures are something that

naturally happens as we write JavaScript

code and it's nice to know how this

feature works there are some Advanced

Techniques that we can do with closures

but they're not used that often so I

won't be covering them in this course

but maybe in a different video now let's

remove

console.log and

save and that's the end of this lesson

in this lesson we learned that functions

are values we learned set time out and

set interval which lets us run a

function in the future we learned an

array method called for each which is a

cleaner way of looping through an array

we used four each Arrow functions and

and add event listener to improve our

projects we learned two more array

methods filter and map and we learned a

feature of functions called

closures here are some exercises to help

you practice what we learned in this

lesson

in this lesson we're going to start the

Amazon Project and we're also going to

learn a very useful technology called

git so first let's take a look at the

Amazon Project to see how it works we're

going to go to our browser

and create a new tab at the top and

we're going to type super simple dodev

SL projects SL Amazon and press

enter so this is going to be the project

we're going to build in this course this

is an e-commerce website that looks like

Amazon where we can see a list of

products on the homepage and then we can

add these products to a cart by clicking

add to

cart and then we can see our cart by

clicking the top

right and on this page it will show us

which products are in our cart and it

will also show us the cost of our order

including shipping and taxes and once

we're ready to create an order we can

click this button to create the order

and it will take us to this page which

shows us a list of our past orders we

can also track our order by clicking

this track package

button and it will take us to this page

which tells us the progress of our order

whether it's preparing it's shipped and

it's

delivered so that's an overview of the

project we're going to built this is a

complex multi-page website where the

different pages interact with each other

to create a full app the first thing

we're going to do is to download the

starting code for this project we're

going to create a new

tab and here we're going to type

github.com

slup

simple Dev SL JavaScript D Amazon d

project and press enter

you can also find the starting code in

the description by clicking

here and then going to the links for

this

lesson and on this page we can see the

starting code for the Amazon Project so

this code contains all the HTML and CSS

that we need the reason we're going to

use some starting code instead of

writing all of this ourselves is because

this course is focused on JavaScript not

HTML and CSS if we were to write all of

this code ourselves it would just take

up too much time and it would be an

entire course by itself if you want to

learn how to create this code you can

check out my HTML and CSS full course

which would teach you all the skills

that you need but for this JavaScript

course we're going to start with the

HTML and CSS here and we're just going

to focus on adding JavaScript to this

website so now let's download all of

this code we can do that by clicking

this green code button here and then

click download

zip once that's finished downloading

we're going to go to our downloads

folder so for me it's this folder right

here called downloads

and then we're going to unzip this file

by double clicking

it and this will give us a folder that

contains all the code so we're going to

select this folder and move it to our

desktop next let's go to our desktop so

we're going to close this for now and

I'll hide the

browser and on the desktop we're going

to select the folder that we downloaded

and we're going to rename this so at the

end we'll remove Main and press enter to

rename it to JavaScript Amazon

Project next we're going to take this

folder and open it in our code editor so

let's open vs

code and we're going to click

file open

folder and we're going to find the

folder that we downloaded for me it's on

the desktop and it's this folder right

here so we'll click this folder and then

click select

folder and then we can close this

welcome

message okay so now we have our starting

code and we're going to set up the

project so first let's open our browser

again and we can close the GitHub

page as well as the tabs for the

previous lessons so we'll close these

tabs right

here but we'll leave the final Amazon

Project

open next let's go back to vs

code and we're going to open this

project in our browser so we're going to

select this file amazon.

HTML so this file corresponds to the

homepage here so let's select this file

and then

rightclick open with live server

so I'm just going to rearrange my

windows here so we can see these side by

side and now we're ready to begin so

let's take a look at the code that we

have to start with as I mentioned all we

have here is the HTML and CSS for this

website there's currently no JavaScript

at all on this

page so one thing you'll notice is that

we can actually create almost all of the

website using just HTML and CSS we

actually don't even need JavaScript to

create all of this we're able to create

the header at the top as well as three

products to start with and this shows

that HTML and CSS can pretty much create

everything that we see visually on the

website where JavaScript comes in is

that JavaScript makes this website

interactive so right now if we click the

add to card button it looks pretty nice

but it doesn't actually do anything and

that's because we haven't added

JavaScript yet so the role of JavaScript

is to make our website interactive after

we created all the content and The

Styling now before we begin adding

JavaScript to this website we're

actually going to take some time and

learn another very useful technology

called git so git is a technology that

lets us track changes in our code for

examp example do not follow along here

but let's say that I'm working on this

website and I go into my code editor and

I change some code here so let's say

that I add some code

here and then in this file I'm going to

delete some code so I just select some

code and delete it and then

save and then in this file I'm going to

change some code at the bottom

so now let's say that I made a mistake

and I want to undo all the changes that

I just made so how would I do that how

would I remember all the code that I

changed in the different files so right

now this is really difficult and this is

a problem that we run into in bigger

projects we're changing lots of code in

different files and it's really hard to

keep track of what code has changed and

this is where git comes in git lets us

track changes in our code and it helps

us solve this

problem so here's what it looks like if

I have git set up in my project I can go

into this section of VSS code this

section is for git and then here git

will tell me which files I changed and

if I click these files it will tell me

which lines I changed and exactly which

code I changed if I want to I can click

this button

to reverse all the changes in this

file I can also click here to reverse

all the changes in all the

files so as you can see kit helps us

track changes in our code and it lets us

easily undo our changes if we need

to and this technology is really useful

in bigger projects like this Amazon

Project where we're going to be changing

lots of code in in many different files

so before we start this project we're

going to learn how to set up and use

git the first thing we need to do is to

install git to do that we can go to this

section of vs code called Source

control now if this section looks like

this with a button initialize repository

that means you already have git

installed otherwise if you're on Windows

you can click this button and then click

open or you can go to this website

directly and then click this link to

download

git once it's finished downloading we're

going to run the installer and then just

go with the default

options if you're using a Mac you can

click up

here and then type

terminal and press enter

and inside here you're going to type git

and press

enter and then click this link and

install

git all right after installing git we're

going to restart vs

code and make sure you have the Amazon

Project

open and now if if we go into the git

section it should look like this with

the button initialize

repository so now that we've installed

git we're going to set up git in our

Amazon Project we can do that by

clicking initialize

repository if this button doesn't work

for you you can also try going to the

terminal menu and click new terminal

and then inside this terminal type kit

in it and press

enter so a repository is just a folder

where changes are being tracked by

clicking initialize repository this

turns the current folder which is

Javascript Amazon Project into a

repository and now all the changes

inside this folder will be tracked by

git so to start off git will tell us

that all of these files are new files

and that's because we just set up this

repository so all of these files are

considered new changes that we're

starting to keep track

of next we need to configure a username

and email with Git now don't worry this

information is not used anywhere online

this is just forget to add an author to

the changes that we make so to configure

a username and email we're going to go

to the

top and open the terminal menu and click

new

terminal and then inside

here we're going to type get config

user.name and double

quotes now if this looks familiar to you

and you've already done this before you

can skip this step and and the next

step so between these double quotes

we'll pick a username that we want to

use so for me I'll use super simple Dev

and press

enter and we'll also configure an email

by typing get config user. Emil double

quotes and between these double quotes

we'll put an email so I'll put Simon at

superimple

dodev and press

enter so now that we configured a

username and email we can close this

terminal next we're going to save these

changes into git so that git will start

tracking any new changes that we make to

save these changes we're just going to

type type a message here describing what

we changed so let's just type the

message add the starting

files and then we're going to click

commit and if this popup shows up we're

going to click

yes so that will take all of our changes

and save them into git so now that we've

saved those changes into git any new

changes that we add will start showing

up here so let's do an example and let's

change some code in a couple different

files for practice so let's click this

icon up here to show our code and let's

go into amazon.

HTML and we'll just change this title to

intro to git and

save and then let's go into checkout.

HTML and at the top let's actually

remove the title and save and then let's

open orders.

HTML and at the top let's just add

something to the title like

page if we

save and then go into the source control

section or the git

section it will tell us all the changes

that we just made in our code in the

three different files if we click one of

these files it will actually tell us

exactly which code that we

changed now if your git section looks

like this where the changes are on top

of each other instead of side by side if

you want to you can change this by

clicking these three dots here making

sure that inline view is unchecked and

also unchecking use inline view when

space is

limited so now it's very easy to undo

this code we can just take the code on

the left and then copy paste it on the

right to undo this change we can also

click here to undo all the changes in

this

file and up here we can also click this

button to undo all the changes in all

the different

files so that's an intro to Git it helps

us keep track of changes in our code and

it's very useful for bigger projects

like this Amazon Project where we're

going to be changing lots of code in

many different files if you want to

learn about git in more detail you can

check out my git and GitHub full course

in the video

description so now that we've setup git

let's start the Amazon Project so first

make sure that this section is empty and

we've reversed all the changes that we

made when practicing

git next let's click the this icon to

show our

files and let's remove the previous

code and we're going to start in the

amazon. HTML

file and let's close the git page and

then open the tab for this file it

should say amazon. HTML up

here so we'll start by creating the list

of products on the homepage so right now

we start with three products if we go to

the final project we're going to add the

rest of the products that you see here

and we're also going to make this

interactive so that when we click the

add to card button it will add this

product to our

cart so let's go back to our

project and in order to create this

we're going to learn the main idea of

JavaScript so when using JavaScript

script we usually do a three-step

process the first step is to save the

data and then we generate the

HTML and finally we make it

interactive let's go through each step

to create this list of

products so right now we have three

products on our page to start with and

we're going to add more products to this

page so let's start by finding the HTML

for one of these products because we can

always just copy and paste this to

create another one now we're going to

learn a very important skill for bigger

projects which is how to find the code

for something on this page so let's say

that we want to find the code for one of

these products we're going to

rightclick and click

inspect and this will bring up the

console and I'm actually going to click

these three dots and click this icon to

move the console to a separate window so

that we can see the whole web page so

now we're going to click this icon in

the top

left and we're going to hover over and

click the thing that we want to get the

code for so I want to get the code for

this entire first product so I'll click

in this

space and this will tell us that the

code for the product is this code a div

with the class product -

container so now we're going to take

this class and then search for it in our

code editor so let's open vs

code and we're going to type contrl f on

Windows or command F on Mac to search

for code in this file so we're going to

search for the class that we saw earlier

which is

product-

container and this will take us to the

code for one of these products so we can

actually click the arrow on the left to

collapse this code and we'll see another

product container which corresponds to

the second product we can click this

Arrow again and we'll see a third

product container which corresponds to

the third

product so that's how we find the code

for something on the page now to add

another product to this page one thing

we can do is to take this HTML and just

make a copy of it at the bottom of the

page however this is not a good idea

because if we add lots of products we're

going to be copying this HTML over and

over and if we expand this you can see

that each product has a lot of HTML code

so we don't want to be copying all of

this over and over again it's going to

be a lot of code and it's going to be

hard to manage in instead another

strategy is to generate this HTML code

using JavaScript so let's learn how to

do that before we can do that we need to

add JavaScript to this page so we're

going to create a Javascript file so

let's click up here to show our

files and first let's create a new

folder to contain all of our JavaScript

code so let's name this folder SC

scripts and press

enter next let's click on our folder and

we're going to click this icon to create

a new file and we'll name this file

amazon. JS and press enter so this will

be the Javascript file for this HTML

file next inside this Javascript file

let's type the code

console.

log

hello just to make sure that this works

and

save next we're going to load this

Javascript file in our HTML file so

let's go back to amazon.

HTML and then at the bottom of the code

we're going to scroll down and then

right above the closing tag for the body

we're going to add a script element

and we're going to give this element an

attribute SRC or Source equals double

quotes and we're going to load this

Javascript file so this Javascript file

is in a folder called scripts so here

we're going to type the folder name

scripts and then a forward slash to go

into the folder and we'll load the file

amazon. JS and

save so now let let's go back to the

page and we'll open the console right

click

inspect and then click the

console and it should display hello so

now we're loading JavaScript on this

page so let's open up vs code

again and we're going to generate all of

this HTML using JavaScript instead so

the first step in our process is to save

the data what does this mean data means

information so in this case the data is

the information about our products for

example the products name the price

ratings and the image so right now the

information about the products or the

data is inside our

HTML so in our code if we click here to

expand this element you can see that the

inform

about the products for example the name

and the image is inside the

HTML so what we need to do is to take

this data and save it inside our

JavaScript so that our JavaScript can

use it so let's go to our Javascript

file and I'm just going to put it down

here so we can see it side by

side and we're going to move this data

into our JavaScript

so let's remove

console.log and let's create a variable

to save the data so we'll type const and

let's name it

products and make it

equal and now we want to create

something that closely matches our data

so in this case we have a list of

products so in here we're going to

create an array because an array

represents a list

and now each product in the list has

many values like an image a name and a

price so we're going to use an object to

represent each product because an object

lets us group multiple values

together so inside this array we're

going to create an object using curly

brackets and now inside this object

we're going to save the data for the

first product so first let's find the

data in our HTML we're going to search

for the product's name by typing contrl

F or command F and we'll search for

black and

gray and this will take us to the code

for the first product so this is the

name of the first product so let's

actually scroll up and we're going to

get get the image for the first product

and we're going to take this and save it

in our JavaScript so let's select this

code we're going to

rightclick

copy and then inside this object let's

create a property called image colon and

then here right click and

paste and let's save this as a string so

at the front we'll type a single quote

and at the end we'll type a single

quote so we just saved the image inside

our

JavaScript let's move on and save the

name inside our JavaScript so we'll

scroll down we'll select this code and

then

rightclick

copy and in this object we'll type comma

and a property called name col in a

string

and we'll right click and

paste next we're going to save the

rating into our JavaScript so we'll type

comma and let's create a property called

rating

colon for the rating there's actually

two parts the stars and the number of

ratings that it has so let's actually

group these two values into an object

because these values are related to each

other so in here we'll make the rating

and

object and each rating will have the

stars and for the socks it's

4.5 comma and the rating will also have

a

count and for the first product it's

87 next let's save the price into our

JavaScript

so we'll create another property called

price and for the first product the

price is

$10.90 however JavaScript has problems

doing math with decimal numbers or

floats like this so a best practice when

calculating money is to calculate in

cents instead of dollars so for this

reason we're going to save the price as

cents so we'll save it as

1,90 as a reminder $1 is equal to 100

cents and because we're saving in cents

it's helpful to rename this property to

price cents

instead so now if we scroll up we just

saved all the information or the data

about the first product into our

JavaScript next let's go to the end here

and type comma and create another object

and we're going to save the data for the

second product into this object so feel

free to pause the video if you want to

try it yourself

first so again let's find this product

in our HTML we'll go to our HTML and

type contrl f or command F to search for

code and we'll search for the name

intermediate

size basketball so now this is the code

for the second product we're going to

scroll up a bit and find the image for

this product and we're going to select

it rightclick

copy and then inside the second object

we'll create an image property just like

we did up

here and we'll save it as a string and

we're going to rightclick and

paste and let's type comma and we'll

save the name inside the second object

so we'll scroll down and select the

name and then right click

copy and then down here create a string

and rightclick and

paste and we'll type a comma and we'll

save the rating

colon

object and we'll save the number of

stars which is

four and the number of ratings that it

has count colon

127 and finally we'll type a comma and

we'll save the price of the product in

cents colon

295 so now the data for these second

product is saved inside our

JavaScript let's go to the end and type

comma and create another object and

we're going to save the data for the

third product inside again feel free to

pause the video to try it yourself first

so let's save the image we'll find the

code for this product in our HTML so up

here we'll typ contrl F or command

F and we'll search for the product name

which is

adults plain cotton

t-shirt and scroll up and we're going to

save the image first so let's select

this right click copy and then down here

create an image property colon and a

string and then right click and

paste and we'll create a comma and let's

save the name in our Javas script next

create a string and then we'll scroll

down here we'll select the

name right

click

copy and then in here right click and

paste and comma and we'll save the

rating colon and object and we have the

number of stars for this one it's

4.5 colon and the

count and for this one it is

56 and lastly type a comma and we'll

save the price in

cents colon

799 and now let's save our Javascript

file now one really important thing is

to make sure that in each of these

objects we have the same property so we

have the image property the name

property and the same rating property

with the same structure we want all of

our objects to have the same structure

so that our code can handle each product

the

same so that's what it means to save the

data we create something in JavaScript

that closely matches the data that we

have on the Page by the way this is

called a data structure because its

structure structures or organizes the

data and this represents a list of

products so we usually use a combination

of objects and arrays to create a data

structure in

JavaScript so now that we've saved the

data the next step is to use this data

to generate the HTML instead of writing

the HTML

manually to generate the HTML we can

Loop through this array and for each of

these products we're going to create

some

HTML so let's go ahead and loop through

this array first we'll scroll down to

the

bottom and we'll type the name of the

array which is products and then we'll

Loop through this array using a for each

method so we'll type Dot 4 Capital each

brackets and inside we create a function

using brackets arrow and curly

brackets and we'll give it a parameter

called

Product so I'm going to move this back

to the top here so we can see more of

the code so the way that for each works

is that it takes each object saves it in

this parameter called Product and then

runs the function so it takes the first

object saves it in product runs the

function function takes a second object

saves a product runs a function and so

on so for each of these products or each

of these objects we want to create some

HTML so inside this function let's

create a variable const

HTML equals and we'll create a template

string using back

ticks and now inside this template

string we're basically going going to

copy all the HTML for one of these

products so let's go back to our HTML

file and how do we find the HTML for one

product so we learned this earlier we

can

rightclick

inspect and then click the top left

icon and click the element we want to

get the HTML for so this HTML represents

one product and we can search for this

class product- container in our code so

we'll go back to our vs

code inside the HTML file we can contrl

f or command F to search for code and

we'll search for the class product Das

container and let's go to the first

result so we'll go to the first result

which is here and let's copy all of the

code inside this ele element one trick

we can do is to click the arrow on the

left to collapse it and then we'll

select all this code and we'll

rightclick

copy and then inside our Javascript file

inside the string we're just going to

rightclick and paste the

HTML and if we need to fix the

formatting we can select all of this

code and then press tab a few times to

add some indexs and here we can remove

the indent and let's

save so now we're basically looping

through the array of products and for

each product we're creating all of the

HTML that we had before so we're

generating this HTML using

JavaScript now let's console.log this

HTML to make sure that it's working

we'll scroll down to the

bottom and here let's

console.log the HTML that we just

created if we

save and then go back to our page right

click and

inspect and click the

console you can see in the console that

we just generated all this HTML and we

generated three of these

let's go back to our

code and scroll

up now one problem here is that in the

HTML that we generate we don't want to

have the name black and gray socks every

time for the second product we want to

have a different name and a different

image and for the third product we want

to have a different name and a different

image so how do we create slightly

different HTML for each

product to do that we're going to

replace this part of the code with

whatever the image property is so for

here we're going to delete it and we're

going to insert the property image into

this string so to insert values into a

template string like this we can use

Dollar open curly bracket Clos curly

bracket and then inside here we're going

to insert the

product. image property so it's going to

take whatever the image property is of

the product and put it inside this HTML

code same thing for the name instead of

black and gray socks every time we're

going to delete this and then insert a

value we're going to insert the

product Dot and we'll insert the name

property this time into this HTML so dot

name and we'll do the same thing for the

other pieces of data so for each product

the number of stars could be different

so instead of 4.5 every time let's

delete this and we're going to insert

the products rating and stars so

product.

rating. Stars

one thing we have to watch out here for

is that this image has to exist so right

now if we substitute the product.

ratings. Stars into this we will get

this image and if we go into our files

by clicking here and open the images

folder and then open the ratings

folder we can see that there's no image

called rating

-4.5 instead there's an image called

rating

-45 so if the rating is 4.5 we should

convert it into 45 so that this image

actually

exists similarly if the rating is four

we should convert it into 40 so that

this image actually exists so in here we

should actually multiply this by 10 so

that this points to an actual image that

exists

here next let's move

on and we'll work on replacing the count

so we'll remove this and dollar curly

brackets and we'll replace it with the

products. rating Dot and the count

property so

count and finally we're going to replace

the price for each product so in here

we're going to remove this and

substitute

product. price

sense and remember that this is a number

in cents but when we display it on the

page we want to display it as dollars so

we're going to divide this by 100

because there are 100 cents in each

dollar so now in the HTML that we're

generating we're actually inserting the

details about each product if we

save and then go back to the console

right click

inspect and

console and look at the HTML that we

generated you'll see that it's different

for each of the products so that's how

we use JavaScript to generate all the

HTML

here so now the last step is we're going

to combine all this HTML together into

one string and put it on the web page

let's go back into VSS

code and to combine all this HTML

together let's create a variable at the

top for combining all the strings

together so we'll type let let's call it

products cap Capital

HTML and make it equal to an empty

string to start and then each time we go

through the loop we're going to add this

HTML string up here so instead of

creating a new variable we're just going

to add products

HTML equals itself products

HTML plus this string and remember a

shortcut for this is to just type plus

equals so this is called the accumulator

pattern we Loop through an array and

each time we're adding to the result so

we're accumulating the result and now

that we combine all the HTML into this

variable we can scroll to the

bottom and let's remove this line

because this doesn't exist anymore

and then after the loop let's

console.log the products

HTML and

save and now if we go into our

console we combined all the HTML for all

the products

together and now the last step is to

take this HTML and put it on the page

and we can do that using the Dom

so let's go back into our

code and to use the Dom we're first

going to get an HTML element from the

page and put it inside our

JavaScript so first let's go to our HTML

file and remember that a product-

container represents one of these

products here so we're going to look for

this element here a div products- grid

so this element contains all of our

products so we're going to use the Dom

to take this element put it into our

JavaScript and replace all the HTML

inside so to put this element in our

JavaScript we're going to give it a

class so let's add a class

js-

products- grid and

save and let's go into our JavaScript so

I'm just going to move this this down to

the bottom again so we can see it side

by

side and then inside our JavaScript at

the bottom we're going to use the Dom by

typing

document. query selector brackets and a

string and we're going to type dot to

select a class and we're going to select

js-

products-

grid so the DOT means we're going to

look for a class called JS products grid

which is right here and it's going to

take this element and put it inside our

JavaScript and now we can change the

HTML inside the element to do that we'll

use the property do inner Capital

HTML and we'll change it to the products

HTML that we created Above So for

products Capital

HTML and

save so it's not going to look any

different but now we're actually

generating all the HTML with JavaScript

and then using the Dom to put this HTML

inside here so now we can actually

delete all of this because we're

generating this with

JavaScript if we save this file

our products will still be here because

even though we deleted the HTML we're

now generating it with

JavaScript now one problem that I see

here is that the price shows up with one

decimal but we actually wanted to show

up as

10.90 so let's scroll up to this part in

the code so we'll scroll up

here and look for Price

sense and the reason this happens is

because price sense is

1,90 so if we divide that by 100 the

result is actually

10.9 if we want to force this to show

two decimals like

10.90 we actually have a special method

that we can use with a number so here we

can add brackets around this to make

sure we calculate this number first and

numbers have a special method called dot

2 Capital fixed and brackets so to fixed

we'll convert a number into a string but

we can tell it how many decimals we want

between the brackets if we type two it

will show two decimals so if we save now

it shows correctly on the page if you're

wondering how to find this method you

can find it by searching in Google or

using an AI

tool okay let's let's take a break here

and take a look at git to see all the

changes that we made so I'm going to

expand this here and we're going to

click the git

section and it's going to tell us that

we changed two files if we click the

HTML

file git will tell us that we deleted

all of the HTML code for the products

which is correct if we open the

Javascript file it will tell us that we

added all of this new JavaScript code

including the data and the loop for

generating the

HTML so git helps us track all of the

changes that we made so now let's

actually take these changes and save

them into git so we can track new

changes at the top let's type a message

to describe the changes that we made so

let's type

generate HTML with

JavaScript and click

commit and yes if this shows

up so now let's talk about the benefit

of generating the

HTML so let's close git for now and I'll

move this to the side

here so the benefit of generating the

HTML is that if we want to add another

product we don't have to copy paste all

of this HTML again all we need to do is

to go up to the data and add the data

for a new product so let's do an example

and add a fourth product to our list so

at the end here let's type a comma and

create another

object and let's go to the final

project and we'll scroll down to this

four fourth product here so we're going

to take the data about this product and

save it in our JavaScript so first let's

create a property image colon string and

we're going to take this image and put

it in here to do that we can rightclick

the image

inspect and then we're going to copy

this Source attribute so we can double

click it and we can select this

attribute

rightclick

copy and then inside our JavaScript

we're going to right click and

paste and at the end we'll type a comma

and create the name

property and a string and we're going to

select this

name rightclick copy and then in here

right click

paste copy comma and a rating property

colon and object we have these Stars

which is five and the

count which is

2,197 and at the end we're going to add

the price in cents colon

1,899 so now if we save this JavaScript

file and then go back to our

project and we scroll down you'll notice

that it automatically added the fourth

product and all we had to do was to add

another object to our array and then our

Loop will handle generating all the HTML

for us so you can see that generating

the HTML with JavaScript is a lot easier

than copy pasting this HTML every time

and that's why we use this

technique next we're going to add the

rest of the products in the final

project now one thing we could do is to

manually copy this over one by one but

to make this easier inside the starting

code I've actually created a file that

contains all the data so if we scroll up

and close this for now and we're going

to go to this data folder and open it

and inside this folder I've provided a

Javascript file called products. JS and

in here it contains an array with the

data for all the products in the final

project so we don't have to create it

ourselves so now let's use this products

array in our code so first we need to

load this file on our page we can go to

our amazon. HTML file and then scroll

down to the

bottom and then at the bottom in the

script element we're going to add

another script element above it so we

type script and then the source is going

to be equal to this Javascript file so

we'll type the folder called data and

then a slash to go into the folder and

load the file

products.

JS so what this does is that it will run

the files one by one

first it will run the products. JS file

and create the array and then it will

run our amazon. JS file and generate the

HTML so back here let's

save and then go back into amazon.

JS so now instead of using our own

products array let's just use the

products array in this

file so we'll go back to to amazon.

JS and we're just going to delete this

array so over here we can click this

Arrow to collapse the code and I'm going

to select it and then just delete

it and

save so now this variable will be coming

from this file if we go back to our

project and scroll down you can see that

we created all the products in our final

project so the way this works is that

inside our amazon.

HTML we're loading two JavaScript files

this Javascript file creates all the

products and then this Javascript file

Loops through the products and creates

all the

HTML so keep in mind that script

elements are loaded one by one so the

order matters we have to first create

the products array and then we can use

it if these two were reversed then the

code wouldn't

work so this is how a real world website

is created we don't write all the HTML

manually instead we save the data for

the website in a data structure like

this and then we use JavaScript to

generate the HTML using the data so now

let's go into get and look at our most

recent

changes so here it will tell us that we

changed two files in the amazon. HTML

file we added a script element and then

in the amazon. JS file we deleted the

products array that we created on our

own so let's type a message to describe

our changes use products. JS file and

then click commit and yes

now one other thing I want to show you

about git is if we go back to our files

here and then open amazon. JS git has a

really useful feature called a history

so we can open this timeline section and

then click this filter icon and only

check git

history and now you can see that we

actually have a history of all of our

changes for this file so if we click the

first line in the history it will show

us that here we added all of the code

and then the second line in the history

we deleted this part of the code so this

gives us a step-by-step history of all

the changes in our code and in git this

is called a version history you can also

see that the messages that we created

when we commit show up here and these

messages help us us understand what was

changed in each version in the

history all right so let's close this

for

now and the last step in the process is

to make it

interactive so let's take a look at our

current

project so we'll go here and open this

tab and let's scroll

up so right now if we click the add to

cart button Buton it doesn't do anything

so we're going to add some JavaScript to

make this interactive and actually add

this product to a cart so first let's

find the add to cart button in our code

we'll go back to our amazon. JS file

close this for

now and to find the code we can actually

just search the text in the button so

inside here let's typ contrl F or

command F and we're going to search for

the text add to

cart and this will take us to the code

for this button so now we're going to

add an event listener to this button and

make it do something when we click it to

add an event listener we're first going

to add a

class

js-

add-2

dcart and then we're going to use the

dawn to add an event listener to this

button so down

here after we've put this HTML on the

page we're going to use

document. Query

selector all brackets and then a string

a DOT and we're going to select all the

js- add to cart so

js- add-2 to- cart so this will give us

a list of all the add to cart buttons on

the page and then we can Loop through

each of the buttons so we can type dot

for each

brackets and then in here we'll give it

a function bracket arrow and curly

brackets and a parameter so the

parameter is going to be the button

element that we got from the page so now

for each of these buttons we're going to

add an event listener so we can do

something when we click the button to do

that we'll type

button. add event

listener brackets and then the event

that we want to listen for which is the

click

event and then a function that we want

to run when we click this button so

brackets arrow and curly

brackets so for now let's just

console.log a message to make sure that

this is working so we'll

console.log added

product and

save and we can also remove this line

for now because we're not using it and

save again and then now on our page

we're going to click add it to

cart and then look inside our console so

rightclick

inspect and click the

console and it displays added product so

now whenever we click one of these

buttons it will display this message so

that means that our code here is working

correctly next we need to figure out how

to add the product to a cart and we need

to figure out what this looks like if we

think about a cart a cart is basically

just a list and inside this list we have

the product that we want to buy and the

quantity or the number of this product

that we want to buy so we can actually

represent this in JavaScript as an array

inside the array we can have some

objects and each object is going to

contain the product and a

quantity so we can use something like

this to represent our cart so let's go

ahead and create create this cart array

now to keep things cleaner let's

actually separate the cart into its own

file so we'll click up here to show our

files and then we'll go into the data

folder and click this folder and click

this icon to create a new

file and we'll name this file cart. JS

and press

enter so this file will contain all the

code related to the cart and the reason

we separate it is to keep our code

organized each file will focus on one

particular thing so inside

C.J let's create our cart so we can just

create a variable const cart and make it

equal to an array so we'll start off

with an MD cart and let's save this

file and now we need to load this file

into our

HTML so we can open amazon.

HTML and again we can just add another

script element so let's add it at the

top to make sure we load the cart before

running the rest of our code so we'll

type less than

script and the attribute

source and we'll load the data folder

slash to go inside cart. Js

and

save so now it will run this file at the

start and it will create an array

representing our cart so now that we

have a cart we need to figure out what

happens when we click a button how do we

add a product to this cart so let's go

back into amazon. JS and we'll figure

this out together so down here this is

the function that is run when we click

the button so in here we have to figure

out how to add this product to the

cart one way to do this is to just add

an object to the cart like this we have

the product's name and the quantity that

we want however when we click this

button how do we know which product

we're supposed to add to the cart to

solve this problem we're going to learn

a feature of HTML called a data

attribute

a data attribute is just another HTML

attribute except the purpose of a data

attribute is that it allows us to attach

any information to an HTML element so

let's do an example and create a data

attribute we're going to scroll up to

the add to card button here and then at

the end of the opening tag after the

class we'll type enter

and then we're going to type data Dash

and then we can type any name that we

want like

product-name and we'll make it equal to

double

quotes and then inside the double quotes

we're going to put the product's name

like a basketball or a t-shirt so to do

that we're going to insert using dollar

and curly

brackets product

AME and

save so now let's inspect the HTML on

the page we're going to rightclick on

this add to card button and

inspect and then in the elements tab it

will show us the HTML for the button and

now you can see that each of these

buttons now has a data attribute called

data- product-name and it's equal to the

product name

so before we continue let's learn the

syntax rules for the data

attribute a data attribute is just an

HTML attribute that means it follows the

same syntax rules we have an attribute

name on the left and an attribute value

on the right the one difference is that

data attributes have to start with data

Dash and then we can give it any name

that we want like product- name but we

have to make sure to separate the words

with a dash this is also known as Kabob

case so the purpose of a data attribute

is that we can attach any information to

an element so here we attached the

product name to this button but we can

also attach the product's image or the

price and so on so now that we attached

the product's name to this button when

we click this button we can actually get

the name and this will tell us which

product we should add to the

cart so let's see what this looks like

in our code so we'll go to our

code and then when we click the button

we're first going to get the product

name from the button to do that we're

going to type button and then the

property dot data set

so the data set property basically gives

us all the data attributes that are

attached to this button so now we're

able to get the product name so let's

console.log this to see what it looks

like

console.log Open Bracket close bracket

and

save and then in here let's click the

basketballs add to cart

button and we'll go into our console

right click

inspect and

console and I'm just going to move this

to the left so we can see it side by

side with our

code so this is what the data set

property looks like it gives us all the

data attributes that are attached to the

element so in our case we have the

product name now this works just like an

object so to access the product name we

just have to type dot product capital N

name so notice that the name gets

converted from Kebab case to camo case

so now if we

save and let's go back to our

website and click the add to cardart

button it will get that data attribute

from the button and display it in the

console if we click the socks at to cart

button this will tell us which product

we should add to the cart so now that we

have the product name let's actually put

this into our cart so let's go into our

code and here let's save the product

name in a variable called const

Product name

equals and then here we're going to add

this to the cart

so we already created a cart variable

here so we're just going to type the

variable cart and we're going to dot

push into the array and let's push an

object because we said we wanted a

product and the

quantity so we'll add an object

containing the product name which is

this variable product

name and a quantity

of

one and that's pretty much it we first

attached the product name to the button

using a data attribute and then when we

click the button we got the product name

out and then we add the product to the

cart so at the bottom let's

console.log thee cart to see what it

looks like if we

save and then go here and open the

console right click inspect

console and let's add a basketball to

our cart so we'll click here and then in

our cart we now have a basketball with a

quantity of one so now let's add another

product to our cart we'll go to the

t-shirt and click add to

cart and now we have two products in our

cart one b basketball and one

t-shirt so now we're successfully adding

products to a cart next let's try adding

one t-shirt again if we click add to

cart and unfortunately this doesn't look

quite right the T-shirt product is

repeated twice and each of them has a

quantity of one what we actually want to

do is we want one t-shirt product with a

quantity of two

because this is how we're going to

display it on the cart page so let's

figure out how to achieve this and we'll

do this step by step first we'll check

if the product is already in the cart if

it is in the cart we'll just increase

the quantity by one if it's not in the

cart We'll add it to the cart so let's

convert these steps into code so the

first step is to check if a product is

already in the cart so how do we do that

let's go back to our

code and one way to check this is we can

Loop through our cart and look for a

particular product name so up here let's

create some new lines and let's check if

this product name is already in the cart

array so we'll type cart and we'll Loop

through the cart using dot for each

brackets and then inside we'll give it a

function brackets arrow and curly

brackets and we'll give this a parameter

and let's just call it an item so an

item will contain a product name and a

quantity so we want to see if this

product name is already in the

card so we're going to check if the

product

name over here is equal to this item's

product name so we'll type equals the

item.

product name and curly

brackets so if the product names match

that means this product is already in

the

cart so let's save this matching item in

a variable so we can use it later so

we're going to create the variable

outside the for each Loop and outside of

its scope so we'll type let matching

capital I item and we'll make it

undefined to start and if we find a

matching item we're going to save it in

this variable so

matching item equals

item so this is how we figure out if a

product is already already in the cart

now the next step is If the product is

in the cart we'll just increase its

quantity by one so we'll type

if

matching item and curly brackets so we

can just type matching item here because

if we did find a matching item it will

be an object which is a truthy value so

in here we're going to increase the

matching items quantity by one using

matching

item. quantity and we'll plus equal

1 and finally If the product is not in

the cart We'll add it to the cart which

is basically what we do here so at the

end we can just type else if we did not

find a matching item curly brackets and

move this code so we'll select it right

click

cut and then in here rightclick and

paste and remove the new lines and

save so now let's go into our project

we'll

rightclick inspect the

console and let's click the add to card

button for the basketball so we'll click

this

and then in our cart we have a

basketball with a quantity of

one let's add a

T-shirt and now we have one T-shirt with

a quantity of one and if we click add to

cart on the T-shirt

again now we have a t-shirt with a

quantity of two so that's how we solve

the problem of combining the quantities

together now there's one last problem

that we have to solve here

which is it's not good to use the

product name to identify the product in

the cart because in an e-commerce

website we might actually have two

products that have the same name but

from different brands so to fix this we

should give each product an ID and this

ID should be unique so no two products

will have the same ID so let's use an ID

to identify these products instead of

using the name we'll go back to our

code and if we open our files here and

go to data products.

JS you'll notice that I've actually

added an ID for each of these products

and this ID is unique so I added it here

to save us a bit of work so we don't

have to create the IDS

ourselves so now let's just use this ID

in our code so we'll go back to amazon.

JS and then in here instead of using the

product name we're going to use the

products ID to identify it in the cart

but first we need to attach the ID to

the button so we'll scroll up and

instead of a data- product name

attribute we're going to use a data

product-id attribute and we're going to

save the

products ID

instead and now down here we're going to

grab the ID from the button to do that

we'll change this to product ID so

remember this gets converted from Kebab

case to cam case and we'll rename this

variable product

ID and then here we'll compare product

ID is equal to the items product

ID and lastly when we add to the cart

we're just going to add the product ID

to the

cart and

save so now if we go to our website and

click add to cart and check our

console and expand this you can see that

we're saving the product ID so that two

products with the same name will be able

to be added to the

cart okay so that's how we make the add

to cart button

interactive and now we finished all

three steps first we save the data for

the website in our JavaScript and then

we use this data to generate the

HTML and finally we made it

interactive and this is the main idea of

JavaScript this is generally how we use

JavaScript on a real

website now let's go back to git so

we'll open our code editor and open the

git section and review the changes that

we made so we'll expand it and then in

the HTML file we just added the cart. JS

file and then in here we just created

the cart array and in our amazon. JS

file we basically added a data attribute

to the button and then down here we made

the button interactive by adding an

event

listener so now let's save these changes

into git we'll type a message to

describe our

changes make add to cart button

Interactive

and click

commit all right so let's close this for

now and the last feature we're going to

create in this lesson is we're going to

make this cart quantity in the top right

interactive so we'll do this step by

step first we need to calculate the

quantity or the total number of products

in our cart and then we're going to put

that quantity

on the page here so how do we calculate

the total quantity of the cart so

remember that the cart is an array of

objects and each object has a quantity

so to calculate the total quantity we

can Loop through this array and add the

quantities together let's go into our

code and we'll open amazon. JS and let's

scroll to the

bottom so here after we update our cart

we're going to calculate the total

quantity so let's create some new lines

and as we saw earlier we can Loop

through the cart array so we'll type

cart dot for each brackets and a

function arrow and curly brackets and

we'll give this a parameter

item so this is going to Loop through

each object in the cart

next we need a variable to store the

total quantity so let's create a

variable up here we'll type let and name

it cart

quantity and make it equal to zero to

start and then as we Loop through this

array we're going to add the items

quantity to this variable up here so

here we can type cart quantity plus

equals the

items.

quantity so this will add up all the

quantities and save it in this

variable so at the bottom let's

console.log the cart quantity to make

sure that this is working so we'll

save and go back to our page and open

the console right click inspect and

console when we click add to cart on the

basketball the quantity will be one if

we click add to cart on the T-shirt the

quantity will be two if we click again

the quantity will be three so looking at

the cart it basically added one

basketball and two T-shirts to get a

total of three so that's how we can

calculate the total quantity of the cart

so now that we have the total quantity

we're going going to put it on the page

here and we can do this using the Dom so

let's go back to our

code and to use the Dom we first need an

HTML element where we're going to put

this quantity so let's find the HTML

element for this number here we can go

back to our page we're going to

rightclick this number and then

inspect and then we can click this icon

in the top

left hover over this number and click

it so this will tell us that the code

for the number is this code right here a

div with a class cart quantity so now

we're going to search for this class

cart quantity in our code so let's go

back to our

code and let's go to the amazon. HTML

file because the header is still in this

file and we'll type contrl f or command

F to search for code and we'll search

for cart Das

quantity and it will tell us that it's

this line right here so next to use the

Dom we need to get this element into our

JavaScript to do that we're going to add

a class to this element so let's add the

class

js- cart D quantity and say

save now let's go back to our JavaScript

file and I'm just going to move it down

here so we can see it side by

side and we'll scroll down after we

calculate the quantity let's get this

element into our JavaScript using the

Dom so at the bottom we'll type

document. query

selector brackets and a string we start

with a DOT and the class

js- cart D

quantity and now that we have this

element we can change the HTML inside

using the property do inner Capital

HTML and we'll make it equal to the cart

quantity that we calculated above so

let's

save and go back to our website and

let's click the add to card button for

the

basketball now it will update the

quantity to be one let's click the add

to cart for the T-shirt it will update

the quantity again and it will be two if

we click it again it will increase to

three so now the cart quantity up here

is

interactive the last thing we need to do

is we'll go back to our

HTML and in instead of starting at three

the card quantity should start at zero

so let's

save and now the cart quantity starts at

zero if we click add to cart it will

increase to one so that's how we create

this cart quantity feature in the final

project so now we're finished all the

features that we're going to do in this

lesson let's go back to our JavaScript

and I'm just going to move it back up

here

and let's clean up this code by removing

these console.

logs and

save and finally let's check git one

more time to see the changes that we

made so we can expand this and go to the

git

section if we click amazon. HTML it will

tell us we added this class and if we

click amazon. JS it will show us the

code that we added for C calculating the

card quantity and putting it on the

page so finally let's type a message to

describe our

changes make the cart quantity

interactive and

commit so now we can close

this and that's the end of this lesson

in this lesson we started the final

Amazon Project

we set up and learned how to use git to

track changes we learned the main idea

of JavaScript which is save the data

generate the HTML and make it

interactive we created a list of

products on the homepage we made the add

to cart button interactive and we made

the cart quantity

interactive thanks for watching this

course so so far if you want to support

this channel you can check out the

premium version of my courses just like

this one where you can get a certificate

of completion and a Better Learning

platform if you're interested in extra

videos from me more in-depth videos and

behind the scenes content you can check

out these links here you can also

support the channel by liking the video

subscribing and sharing this video with

others thanks again and let's continue

with the course

here are some exercises to help you

practice what we learned in this lesson

in this lesson we're going to learn a

feature of JavaScript called modules

which is a better way to organize our

code so first let's take a look at a

problem that we have in our current code

we're going to go to our files here and

we're going to open amazon.

HTML and then we're going to scroll to

the bottom of this file to our script

tags so right now we're using three

script tags to run all of our

JavaScript so this runs all the code in

cart. JS and then it runs all the code

in products. JS and finally it runs all

the code in amazon. JS so this is

basically the same thing as combining

all the files together into one big file

and then running all of our code however

there's a big problem with using script

tags like this and that problem is it

can cause naming conflicts so in our

situation here we created a variable

named cart in cart. Js

this means we can't use the variable

name cart in any of our other files so

for example if we went to amazon.

JS and then we scroll to the top

here and let's say that we try to create

another variable named cart so at the

top we type const cart equals square

brackets and

save and now if we go back to our

project you'll notice that the website

stops working and if we rightclick

inspect and open the

console it will tell us that we got an

error and it says that cart has already

been declared so this is happening

because we created a variable called

cart in cart. JS and then later in

amazon. JS we created another variable

named cart now we can't have two

variables with the same name in

JavaScript and this causes an error and

it causes our website to break so this

is called a naming conflict when we have

two variables with the same

name so the big problem with script tags

is if we go back to our

code you can see here that it's really

hard to tell which variables have been

created in other files and it's really

easy to accidentally create a naming

conflict like this so that's the problem

with using script tags like this and

running our code one file at a time it's

very easy to get naming

conflicts so now we're going to learn

how to solve this problem using a

feature of JavaScript called

modules so a module basically contains a

variable inside a file so now this

variable is not going to cause conflicts

with anything outside the file for

example in our project we created a

variable called cart and we want to

contain this variable inside the cart.

JS file so that it doesn't conflict with

the cart variable inside the amazon. JS

file so we can do this using a module so

now let's learn how to create our first

module we're going to go back to amazon.

HTML and then here to create a module

we're simply going to delete this line

of code that uses a script tag to load

cart. JS so we'll delete it and

save and you'll see that the website is

working again so how does this work when

we use a script tag it will run all the

code inside cart. JS so this code will

create a card variable and this will

cause a naming Conflict by removing the

script tag we're no longer running the

code inside cart. JS so we're no longer

creating a cart variable and it will no

longer cause a naming

conflict so to create a module we simply

do two steps number one we create a file

and write our code inside the file and

number two don't load the file with a

script tag by doing this any variables

we create inside the file will be

contained inside the file and it won't

cause naming conflicts so that's

basically how we create a

module okay so now we run into another

problem in our code if we open amazon.

JS we created this card variable as an

example but what we actually want to do

is to keep the cart variable inside

cart. JS because we want to keep all the

code that's related to the cart inside

this file so in

and if we

save and then go back to our project and

click add to cart you'll notice that it

no longer works so let's look at the

console again to see what error we get

we'll right click

inspect and open the

console and it's going to tell us that

cart is not defined so the problem that

we have here is that in this file we're

using the variable cart but now because

we're not loading cart. JS using a

script tag the cart variable doesn't

exist anymore it's contained inside

cart. JS and we can't access it from the

outside so now we're going to learn how

to get a variable out of a file or a

module to do that we're going to do

three steps the first step is to add a

type equals module attribute the second

step is to export and the third step is

to import let's learn these steps one by

one so the first step is to add a type

equals module attribute we're going to

open amazon.

HTML and we're going to scroll to the

bottom and here in the last script tag

where we load amazon. JS we're going to

add an HTML attribute here so we're

going to type type equal equal module

and

save so the type equals module attribute

basically lets this file get variables

out of other files it basically enables

this feature now the second step is to

export so we're going to go to cart.

JS and now we're going to choose which

variables can be accessed outside of

this file so for example we want to

access the VAR variable cart outside of

this file to do that in front of the

variable we're just going to type the

word export and space and save so now

this variable can be used outside of

cart.

JS the last step is to

import so we're going to go to the place

where we're going to use this variable

which is inside amazon.

JS and now at the top we're going to

tell the computer which variable we want

to get from another file so we'll type

import open curly bracket close curly

bracket and between these brackets we're

going to give the name of the variable

we want to get which is the cart

variable and then we'll tell the

computer which file we want to get this

variable from so we'll type

from single quotes and and

semicolon and now inside these quotes

we're going to locate the file using a

file path so let's open up our files

here so it's easy to see what files we

have so right now we're in amazon. JS

and we want to locate cart. JS so the

first step is we actually need to get

out of the scripts folder we're in the

scripts folder and we need to get out of

it and into the data folder so to get

out of the current Cent folder that this

file is in we're going to type dot dot

so dot dot basically represents the

folder outside of this current folder

which is this folder right here

JavaScript Amazon projects and then

we're going to type a forward slash to

go outside of the scripts folder so now

that we're outside of this folder we're

going to go into the data folder so here

we're going to type data and then a

slash to go into this folder and we're

going to locate the file cart. JS

C.J and

save so what this code does is that it's

going to take the variable cart out of

the file cart. JS and we use this file

path here to locate that file so as a

reminder dot dot means to go outside of

the current folder outside of scripts

into here and then we go into the data

folder and then inside the data folder

we find cart.

JS so those are the three steps to get a

variable out of a module first we add a

type equals module attribute to enable

this feature and then we export the

variables that we want to get out and

finally we import the variables when we

need

them now there's two more things that we

need to know about modules number one we

have to put all of our Imports at the

top of the

file and number two in order for modules

to work we need to use live server so

for example if I open the folder that

contains amazon.

HTML so I open JavaScript Amazon Project

and then I select this HTML file and

rightclick open with Google

Chrome the website won't work and that's

because modules don't work if we open

the HTML file directly like this so

let's close this for

now and to get modules to work we need

to open our code editor and then

rightclick the HTML

file and open with live

server so in this course in order for

modules to work we need to use live

server to open our HTML files

so now that we learned how to use a

module let's talk about the benefits of

modules the first big benefit is that it

helps us avoid naming conflicts the only

time that this causes naming conflicts

is if we import this variable and we

have another variable named cart inside

this file like

this so this will again create a naming

conflict if I save this the website will

stop working but at least now we have

control over when naming conflicts

happen they will only happen if we

import the same variable name now

modules have another feature that allows

us to avoid this problem as well so

after the variable name that we import

we can type as and then a different name

such as my cart and save so this will

basically take the input and rename it

to my cart so that this will no longer

conflict with this variable name so as

you can see modules have a lot of

features that help us avoid naming

conflicts when we have lots of files in

our project so now I'm just going to

delete this and put the code back

because that was just an example and

save so the second big benefit of

modules is that we don't have to worry

about the order of our files

before when we loaded everything with

script tags we had to make sure that we

load C.J first because we need the cart

variable to be created and then we can

use it in amazon.

JS so the order of our script tags

really matter and it becomes really hard

to manage when we have lots of files in

a big

project but now with modules we can just

import the variables that we need and we

don't have to worry about the order that

we're loading our

files so as you can see modules are a

better way to organize our code

especially in bigger projects so now

let's use git and save our changes so

we'll go to the git section here and it

will tell us we changed three files in

amazon. JS we removed the script tag and

added type equals module in cart. JS we

exported the cart variable and in

amazon. JS we imported the cart variable

from cart. JS so now let's save these

into get so here we'll type a message

use

modules and import cart from cart. JS

and

commit now that we learned modules let's

use them in more places in our project

so let's close this for now and we're

going to open amazon.

HTML and next we're going to turn

products. JS into a module as well so

we'll start off by deleting the script

tag because the script tag will just

load all the code onto the page so we'll

delete this and

save so notice that our website stops

working and now inside amazon. JS we

need to to access products from

products. JS so again we're going to do

three steps the first step is to add a

type equals module attribute which we

already have so we don't need to do this

again the second step is to export the

variables that we want to get out so in

this case we want to get the products

variable out of the products. JS file so

let's open our files and open products.

Js

and we'll scroll to the

top so to get the products variable out

of this file in front of the variable

we're going to type export and space and

save and the last step is to import the

variable that we need so inside amazon.

JS we need the products variable so at

the top we're going to type

import curly brackets

and then inside here we're going to type

the variable name that we want to get

which is

products and we're going to get this

variable from single quotes semicolon

and then inside here we're going to

locate the products. JS file so we're

going to type dot dot and slash to go

outside of the current folder so outside

of the scripts folder and then we're

going to go into the data folder so type

data and a slash to go into the folder

and we're going to locate the file

products. JS and

save so now that we're importing this

variable from this file the rest of our

code will work and our website will

start working

again so that's how we turn products. JS

into a module as well so let's go into

get and take a look at our

changes so in amazon. HTML we deleted

the script tag and then in products. JS

we exported the variables that we wanted

to get out and then in amazon. JS we

imported the variables that we need from

the

file so let's type a message and save

these changes into git import products

from products. JS and

commit let's close

this and let's open amazon.

HTML now the last thing is you might be

wondering should we also delete this

script tag that loads amazon. JS and the

answer is no because we still need one

Javascript file to load our code so this

file will import from all the other

files that we created

and this is how we organize our code in

a real

website so this file is called the entry

point so now that we've seen some

examples of modules we're going to use

modules to organize our code better so

let's go into amazon.

JS and then we're going to scroll down

to the code for the add to card button

so inside this file we're going to

scroll down here all the way down to

this code here so this is a code that we

run when we click add it to cart and

you'll notice that we're running a lot

of code here when we click that button

we're running code that adds the product

to the cart and we're also running code

that calculates the quantity and updates

the page so a best practice in

programming is that when we have a lot

of code here that does different things

it's better to split these up into

smaller functions to make our code

easier to read so here this part of the

code takes the product ID and then adds

it to the cart so it makes sense to

split this into its own function so

let's scroll up and at the top here

let's create a function for this code so

we'll type function and let's call it

add to cart brackets and curly brackets

and then we're just going to move all

this code into the function so we'll

select this

code and then

rightclick

cut and then inside this

function rightclick and

paste and then down here we're going to

run this function inside here so when we

click add to cart we're going to run add

to cart function that we just created

and Save

so now let's give this a try so we'll

click add to

cart and unfortunately it doesn't work

anymore so let's take a look at the

console to see if there's any errors

we'll rightclick

inspect and then open the

console and it's telling us that product

ID is not defined so if we look at our

code

here and scroll up in the function

you'll notice that we're using product

but it's no longer anywhere in the

function and that's because product ID

is outside the

function so we actually want to keep

this code outside because it's using

this button so instead we're going to

take product ID and put it into a

function using a parameter so at the top

of the function we're going to add a

parameter product

ID and then when we call this function

we're going to pass it the product

ID so we're going to take this value put

it into the function and save it in here

and then the function can run as normal

so now if we save and then go to our

project and click add to cart you can

see that it's working

again next let's go back and scroll

down and we're going to put the rest of

our code into its own function as well

to make it more organized so at the top

here let's create some new lines and

create a

function and this code updates the card

quantity on the page

here so let's name this function

update cart quantity brackets and curly

brackets and we'll move this code into

the function so let's select this code

and then rightclick cut and then in here

rightclick and

paste and then down here we'll call the

function using update cart quantity and

brackets and

save so as you can see by splitting up

our code into smaller functions it makes

our code a lot easier to read when we

click add to cart it's really easy to

understand what's going on first we're

going to add a product to our cart and

then we're going to update the card

quantity so now let's save and then go

back to our project and try it out and

you can see that everything is working

again so we're going to do two more

things to better organize our code so

let's go back to our code and the first

thing is we're going to scroll up to the

add to cart function and I made a small

mistake in the previous lesson I

actually want to rename this parameter

from item to cart item instead to make

it a little more clear so we're just

going to rename this to cart item and

here as well we name it to cart item and

save and we'll scroll down here and

we're going to do the same thing for

this parameter so we'll rename it to

cart item and then here cart item and

Save

and the last thing we'll do is let's

scroll up to the add to cart

function so you'll notice that this code

manages our cart so it's actually a best

practice to move this function into

cart. JS because cart. JS contains all

the code that's related to the cart a

best practice is to group related code

together into its own

file so here let's take the function add

to cart we'll select it and then

rightclick

cut and then inside cart. JS we're going

to rightclick and paste and just move

that function into this file because

this file contains all the code that's

related to the cart so now that this

function is inside the file we need to

access it from amazon.

JS and we can do that using modules

using the features export and import so

inside cart. JS in front of the function

we're going to export it so we can use

it in other files so let's save this

file and then inside amazon. JS we're

going to scroll to the

top and you'll notice that we're already

importing something from cart. JS so we

actually don't need to write import

again here we can actually import

multiple things from this file by typing

comma and space and then something else

that we want to import so in our case

we're going to import the function add

to cart so here we'll type comma add to

cart so now it will import both the cart

and the add to cart function from this

file so Imports can import multiple

things from a

file Imports have another syntax import

Star as this Imports everything from a

file and groups it together inside this

object and then we can access each

import as a property or a

method so lastly I'm just going to

scroll down to my code

here and I'm just going to remove this

extra new line and

save now you might be wondering if we

should move update cart quantity into

cart. JS as

well so this function actually handles

updating the web page rather than

managing the cart so we're going to keep

this function inside this file for

now so now let's go into get and save

our changes so we'll go here and inside

cart. JS we moved the add to cart

function and then we exported it and

then inside amazon. JS we imported the

add to card

function and then down here we took the

big block of code that we had before and

we separated it into two functions add

to cart and update cart quantity and

this made our code a lot easier to

read so now let's type a message

describing our changes move add to cart

into cart. JS and commit

next we're going to create the checkout

page in our final project and we're

going to use modules to organize our

code again so let's open the final

project and we're going to click this

cart icon in the top

right and this will take us to another

page which is the checkout page so on

this page we can see the products that

are in our

cart so if you're wondering how that

cart icon works it basically uses is an

HTML element called a link element which

looks like this link elements have a

special attribute called href when we

click a link element whatever is inside

the href attribute it will open it in

the page so if we put youtube.com inside

the href and we click the link it will

open youtube.com in our browser if we

put a file like checkout. HTML inside

href it will look for a file called

checkout. HTML and open that

file so in our project if we look at our

code and open our

files inside amazon.

HTML we're basically just using a link

element or an a element and this has an

hre of checkout. HTML so what this does

is it's going to look for a file called

checkout. HTML beside the current file

amazon. HTML so here's amazon. HTML and

it's going to look for checkout. HTML

beside it and then open that in our

browser which is how that cart icon

works so in our browser at the top you

can see that it opened checkout. HTML so

that's basically how a link element

works and how we can navigate from one

page to another you can learn more about

link elements in my HTML and CSS full

course but for now now we're going to

learn how to build the checkout page

using

JavaScript so first let's take a look at

the code for this page so again the code

is inside checkout.

HTML so in our code editor we're going

to open checkout.

HTML and this is a code for the page

that we saw earlier that contains our

cart so just like with the homepage

instead of writing all this HTML

manually we're going to use JavaScript

to generate this

HTML so first we need to add JavaScript

to this page so let's scroll down to the

very bottom

here and right before the end of the

body we're going to create a script

element to load some

JavaScript and we'll give it an

attribute Source equals double quotes

and then a file we want to load so let's

create a new Javascript file file for

this page so inside our scripts folder

let's click amazon. JS and then click

this icon to create a new file and let's

name this file checkout. JS and press

enter and now we're going to load this

page inside checkout.

HTML so here in the source attribute

we're going to locate this file so first

we need to go into this scripts folder

so we'll type

scripts and then a slash to go into the

folder and then we'll load the file

checkout.

JS and next we're going to add another

attribute type equals double quotes

module so remember from earlier in the

lesson this attribute enables module

features for this file so now this file

can import from other JavaScript files

so now let's

save and let's open checkout. JS and

we'll start creating this page with

JavaScript so let's go back to our page

first and take a look at the structure

of this page so you can see on this page

we actually have two sections we have

the cart section on the left which shows

the products in our cart and we also

have the payment section on the right

which calculates the cost of our order

so let's use JavaScript to create the

cart section first so remember the main

idea of JavaScript is first we're going

to save the data and then we're going to

generate the HTML and finally we'll make

it

interactive let's start by saving the

data that we need for this section of

the page so for this section we're

basically displaying a list of products

along with the quantity of each product

that we want to buy and and if you

remember we already created a data

structure to represent this which is our

cart inside our cart we have the ID of

the product as well as the quantity that

we want to buy so we can just reuse this

data structure to create this section so

let's go into our

code and we're going to open cart.

JS so inside here we have an array

called cart that's supposed to represent

our data here

so right now our card is empty so to

make it easier for us to develop we're

just going to add some default values

into this array so inside here let's

create an object and put one product

into our card first so looking at this

page the product that we want to put is

the socks so we'll go back into our code

and I'll rearrange my windows so we can

see it side by side and we're going to

get the product ID for the socks here so

we're going to go into products.

JS and then here's the socks we just

going to take this

ID right click

copy and then inside the

cart and remember we structured our data

so that each card item has a product ID

as well as a

quantity so here we're going to create

the same structure that our current code

uses

so we're going to give each object a

product ID colon and single quotes and

we're just going to rightclick and

paste the ID that we copied earlier and

then we'll type a comma and we'll give

it a

quantity colon and for the first item

we're going to give it a quantity of two

so we'll just create a cart that kind of

matches what we see on this page

next let's create a second card item to

represent the basketball so we'll type

comma curly brackets we'll give it a

product ID colon and single quotes and

then we're going to get the ID for this

basketball so inside products. JS we

going to scroll down to the basketball

here and we're going to copy this

ID right click copy

and then inside cart.

JS in here right click and

paste and we'll give this one a

quantity colon one and

save so what we're doing here is we're

just creating some default values that

we can use to write the code to generate

this page so this is just for

development when we're actually using

the website the cart will start off as

empty so so if we compare our data to

our page you might notice that there's a

few things that are missing such as the

product's image the name and the price

so how come we're not saving these into

our data and that's because we're using

a special technique we're just saving

the product's ID and then we can use

this ID to search for this product

inside the products array here so using

the ID we can find all the other details

of the product like the image the name

and the price so there's no need to save

this data twice inside the products

array and inside the cart array all we

have to do is save the ID of the product

that we want and then search for it so

this technique is called duplicating the

data or normalizing the data and this is

a very common technique in software

engineering okay so the one other thing

that we probably need to save in our

data is the delivery times and the

delivery options but we're going to

leave this for the next lesson because

it requires some more features that

we're going to

learn so for now we finished saving the

data that we need the next step is to

use this data to generate the

HTML so let's open checkout.

JS so I'm just going to drag it to the

bottom here so we can see it side by

side

so the first step we need to do is to

take the cart array and import it into

checkout. JS so we can use it so in here

let's import curly brackets the cart

array and we're going to import it from

single quotes and semicolon and we're

going to use a file path between the

quotes to locate cart. JS so let's open

our files again and to get from here to

here we need to go out of the scripts

folder so to do that we can type dot dot

and then slash to go to the outer folder

and then we're going to go to the data

folder so we'll type data slash to go

into this folder and we'll locate cart.

JS so cart. JS and save and next we're

going to Loop through this cart and

generate the HTML just like we did for

the

homepage so let's close this for now and

here we're going to create a loop over

the cart so we'll type cart. for each

brackets and a

function and then we'll give it a

parameter let's call it cart

item and then for each cart item here

we're going to generate this

HTML so in here let's create a template

string for the HTML using back ticks and

we'll create some new lines and then

here we're going to copy and paste the

HTML for one of these products so first

let's find the HTML for one of these

products and to do that we can

rightclick

inspect and then click this top left

icon and then click the element we want

to get the HTML

for so here's the HTML for one of these

products and we're going to search for

this class card item container and our

code so inside our

code let's open checkout.

HTML and we'll type control F or command

F to search for code and we'll search

for the class cart D item D

container which is this code right here

so if we collapse it and collapse this

this is the code for these two products

here so we're going to take this HTML

and we're going to move it into our

JavaScript so we can generate it with

JavaScript so we'll right click

copy and then in here right click and

paste and if we need to fix the

formatting we can select all of these

lines and then press shift tab to remove

some indents

and I'll add an indent here next when

we're generating this HTML we want to

replace this with the actual products

image and this with the actual products

name so we're going to take this card

item and use it to get the data that we

need so let's open card. JS to see what

each cart item looks like so we have the

product ID and the

quantity so first we need to use this

product ID to search for the product in

order to get the other details like the

image the name and the

price so to do that let's get the

product ID out of the cart item first so

we'll create a variable const product ID

equals the cart item do product

ID and now we need to use this to search

for the full product so the full product

if we open our files is INS inside

products.

JS which is this array right here so I'm

just going to move this up here so we

can see it side by

side so to search inside this array we

actually need to import products into

checkout. JS so let's use some module

features again at the top we'll import

curly

brackets the products array and we'll

import it from single quotes and

semicolon and then here we'll locate the

products. JS file so we'll type do dot

slash to go out of the scripts folder

and then we'll go into the data folder

data and then a slash to go into this

folder and we import from products. JS

so

products. JS and save so now we have

access to this products array here and

we'll search the array for the full

product details so down

here let's create a variable to save the

result so we'll type let and we'll name

it matching

product and then down here we'll Loop

through the products array so we'll type

products. for each brackets and a

function and then we'll give it a

parameter

product and now for each product here

we're going to check if the ID property

is equal to our product ID here so down

here we'll check if the

product. ID property is equal to our

product ID up here and then if they're

equal that means we found the matching

product and we're going to save it in

this variable so matching

product equals this product that We're

looping

through so now that we have the matching

product we have access to the image the

name as well as the price that we can

use to generate this HTML so this is a

good example of duplicating or

normalizing our data so now at the

bottom let's

console.log our matching product to see

if it works so matching

product and

save now if we go into our project and

we rightclick inspect and check our

console you can see that we were able to

get the full product details for each of

these products using the product ID so

now that we have the full product

details we can use this to generate all

this HTML

so down here instead of generating the

same image every time we're going to use

the image in the matching product so

let's get rid of this

code and here we're going to remove this

and we're going to substitute using

dollar curly

brackets the matching

product.

image and we'll scroll down and instead

of the same product name every time

we're going we're going to replace this

and we're going to substitute the

matching

product. name so each time we're going

to generate HTML with a different image

and a different name and down here the

same thing remove the price and we'll

replace it with matching product Dot and

then we'll just check here what the

property is it's called a price sense

and remember this is in

and to display it as dollars we have to

convert it by dividing by 100 and

save and lastly we're going to replace

the quantity here so if we scroll down

we can see that this is the quantity so

instead of two every time we'll

substitute and for the quantity remember

it's not part of a product it's part of

our cart so each cart item has a

property called called quantity so down

here we're going to substitute the cart

item.

quantity and

save so now we're generating all this

HTML by looping through our cart so the

next step is we're going to combine all

this HTML together and then put it on

the page so I'm just going to move this

up here so we can see more of the

code so to combine all this HTML

together let's create a variable up here

to store the result so we'll type let

and let's call it the cart summary

HTML equals an empty string and now each

time we Loop through the cart we're

going to add this HTML up here so that

we combine it so here we'll type cart

summary

HTML Plus

equals this HTML that we

generated and at the bottom I'll just

add a

semicolon and then let's console.log the

cart summary

HTML

console.log cart summary HTML to make

sure that it worked so we'll save and

then in here we'll check the console

right click

inspect the console

and now you can see that we generated

the HTML and each cart item is different

depending on the product that is being

displayed so that's how we generate all

the HTML for this section and the last

step is to take this and put it on the

page using the Dom so first we need an

element that we can put the HTML inside

of to find this element let's rightclick

inspect and click the top left left and

click one of these

products and let's find this order

summary element because this contains

both of our products here so we're going

to replace all the HTML inside here with

what we generated so let's search for

the class order summary in our code so

we'll go back to our code and let's open

checkout.

HTML and we'll type contrl f or command

F to search for code and we'll search

for the class

order-

summary and then it's right

here and we're going to add a class so

we can select it using the Dom so js-

order- summary and

save so now let's use the Dom and put

this element in our JavaScript so inside

here at the

[Music]

bottom we use

document. Query select VOR

brackets and the class we just

created js-

order-

summary and we'll use the property.

inner Capital

HTML and we'll change the HTML to cart

summary

HTML and we can remove this

line and now if we

save we're basically generating all this

h HTML with JavaScript and then putting

it on the page so now we can go back to

checkout.

HTML and we can actually remove the code

inside this order summary so we can

delete this

code and save and everything will still

work because this is now being generated

by

JavaScript so that's how we create the

cart section of this page with

JavaScript let's go into get and save

our changes so we'll open the git

section and then it will tell us that we

changed three files in checkout. HTML we

removed all the HTML that was written

manually and then at the bottom we

created a script tag to load our

JavaScript and then we also changed

cart. JS and added some default values

to work with and then we created

checkout. JS which loops through the

cart creates the HTML and puts it on the

page so let's create a message to

describe our

changes generate

HTML for the order summary and

commit next let's open our project

again and before we continue we actually

have two issues that we need to fix the

first issue is that the price is

displaying as one decimal here instead

of two and the second issue is that

these delivery options are actually

shared between the two products for

example if I click this delivery option

here it will actually unselect for the

second product so they're sort of shared

between the two

products but what we actually want is

for each product to be able to select

its own delivery options so we're going

to fix these two issues

next first let's focus on the price and

we want to display it in two

decimals so we actually learn how to fix

this on the homepage using the method to

fixed so we're going to use the same

code here let's go into our

code and we'll open our files and let's

open checkout. JS

again so here we're going to scroll down

to where we display the

price which is here price sense and to

show this in two decimal places we're

going to surround this with brackets to

make sure we calculate it

first and then use the method

do2 fixed brackets and then two to show

two decimal places if we save and then

open our

project now the price is displaying

correctly before we move on we're going

to learn how to better organize this

code so if we go

back so notice that we're using this

code inside the checkout page as well as

inside amazon. JS which is the homepage

so we can actually share this code

between the two files so we don't have

to repeat it and to do that we can use

modules so let's open checkout. JS again

and what we'll do is we're going to

create a function that does the same

thing as this code and then we can share

this function between the two files so

let's create a file that's going to

contain this shared function so we're

going to go to our scripts folder here

and inside we're going to create a new

folder this time and let's call this

folder

utils and press

enter so we're naming it utils because

this code is sort of like a useful

utility that we want to

share now inside this folder we're going

to have different types of utils so

let's create a new

file and let's name it money. JJs so

this file is going to contain utilities

that are related to money which is this

code right here so let's press

enter and I'm just going to move this to

the bottom so we can see it side by

side so now inside this UIL file we're

going to create a function that does the

same thing as here and then we can share

it between the two

files so here we'll create a function

and let's name it format currency

because that's what this code is doing

and then brackets and curly

brackets so this function is basically

going to do the same thing as here so

we're going to add a parameter here

price sense

because we want to use this function for

any amount of price

sents and then in here we're going to do

the same thing which is price sents

divided 100 and then we're going to

surround this with brackets to make sure

we calculate this

first and then display it in two decimal

places using dot 2 fixed brackets and

two and finally let's return this result

return and

save so what we just did is we created a

function that does the same thing as

this code here and now we're going to

share this function between checkout. JS

and amazon. JS so first in order to

share it we need to export this function

so at the front we're going to type

export and

save and now inside each of these files

we're going to to import this function

and use it so let's scroll to the

top and here we're going to import curly

brackets we're going to import the

function format

currency and we're going to import it

from single quotes and

semicolon and then inside here we're

going to locate the file money. JS so

here we're in the checkout. JS file

which is right here and to go here we're

first going to go into the UTS folder so

we're going to Type U toils and then a

slash to go into this folder and we're

going to locate the file money. JS so

money.

JS now for modules we have to do one

extra thing at the front of this file

path we need to type dot

slash so remember that dot dot

represents the folder outside the

current folder so for checkout. JS if we

go outside of this folder we're going to

go outside the scripts

folder now a single dot on the other

hand means the current folder so this

dot means we're going to go into the

current folder which is the scripts

folder and then we're going to go into

the utils folder and then we're going to

go and locate money.

JS so for modules if we want to start in

the current f folder our file paths have

to start with Slash so that's one extra

thing that we have to do so now that

we've imported the format currency

function let's use it in the rest of our

code so we're going to scroll

down to here and instead of writing this

all over again we're just going to use

the function format

currency and then brackets and we're

going to remove the rest of the code

here and and close bracket and

save so we're basically running the same

code except we're using this shared

function that's located in another file

so let's open our

project and we can see that the price is

still displaying

correctly so now let's go back into our

code and we're going to share this

function inside amazon. JS as well so

let's open amazon.

JS and then we'll scroll to where we

show the price which is here and we're

going to use this function again so

first we have to import it so we'll

scroll up to the top and import curly

brackets we'll import the function

format

currency and we'll import it from single

quotes semicolon and then here we'll

locate the file money. JS so remember

for module if we want to start in the

current folder we have to type slash and

then we're going to go to the UIL folder

so utils and then a slash to go inside

the folder and locate the

file money.

JS and now we're going to use this

function so let's scroll

down and we're going to replace this

code and use format currency and

brackets so we can remove the rest of

the code here and

save and now let's look at our

project and we'll click up here to go

back to the

homepage and you can see that the prices

are displaying as two decimal

places and that's it if we look at our

code again we're essentially taking this

function and sharing it across two files

using modules so using modules we can re

use a lot of our code and reduce

repetition next let's work on the second

issue that we saw earlier so we'll go

back to our project and click the top

right to go back to the checkout page

and then here the delivery options are

shared between the two products but we

want each product to choose its own

delivery

options so to fix that let's go back

into our code and just going to resize a

here so we can see it side by

side and we'll open checkout. JS again

and we can close this for

now so this is an HTML element called a

radial selector and here's the code for

a radial selector so the way that radial

selectors work is that if a set of radio

selectors have the same name then we can

only select one of them so for example

if these three radio selectors have the

same name attribute then we can only

select one of them now if the three at

the top have one name and the three at

the bottom have a different name then we

can select one from the first three as

well as one from the second

three now what's the problem with the

radial selectors here well let's take a

look at the code for these selectors to

do that we're going to rightclick one of

them and then

inspect and then click the top left and

click one of these selectors to get the

HTML code so here we have the code for

the radio selector and you can see that

the name of the selector is delivery

option one and now if we click the top

left again and find one of these bottom

selectors you'll notice that these also

have the name delivery option one so all

six of these have the same name at

attribute that's why we can only select

one of these six at a time so what we

actually want to do is we want the first

three selectors to have one name and the

second three selectors to have a

different name so let's figure out how

to give these a different name so inside

the console we can see the code for this

selector and we have a name attribute

delivery D

option-1 so let's actually find this

name in our code so we'll go to our code

editor and contrl F or command F to

search for code and we'll search for

delivery Das

option-1 and if we scroll

down you'll notice that every time we're

generating these radio selectors we're

always using the same name delivery

option one so every product is going to

have the same name for the radio

selectors and all of these are going to

be shared so what we actually want to do

is instead of using the name delivery

option one every time each product is

going to use a different name for these

three

selectors so one way we can do that is

instead of the number one every time we

can replace it with the product's ID

because the ID is always unique for each

product so let's substitute using dollar

and curly

brackets the product

ID and then down here as well instead of

using the name one every time we're

going to

substitute

product. and

actually we use the name matching

product so we'll scroll down and just

update this to matching

product and then down here matching

product and and as well down here

instead of one every

time substitute the matching product. ID

and

save so now these three radial selectors

will have a different name attribute

than these three radial selectors that

means we can select one out of these

three and we can select one out of these

three so that's how we fix that error

instead of using the same name delivery

option one every time we're going to

generate a name using the product's ID

so let's go into get and save our

changes so in amazon. JS we imported

this shared function and we used it to

format the price in two decimal places

and then in checkout. JS we also used

the shared function

here and we fix the radio selectors

and then in this file

moneyjar

function so let's create a message to

describe our changes fix price

formatting and radio

selectors and

commit the last step in our process is

to make it

interactive so I'm just going to close

these for now

and going to move it to the right again

so we can see our

project and for the order summary

there's a few things we can make

interactive for now we're going to start

with this delete link when we click this

link it should remove this product from

the cart so we're going to learn how to

build

this so let's go back to our code and

first let's add event listeners to all

of these delete links to do that we're

going to find the code for these delete

links so we'll rightclick

inspect and then in here this is the

code so we're going to search for this

class in our code editor delete quantity

dlink so in here let's open checkout. JS

and we're going to contrl f or command F

and search for delete - quantity

dlink which is right

here next we're going to add a class to

these elements so we can add event

listeners so at the end here let's add a

class

js- delete

daslink and

save and then at the bottom we're going

to scroll down and then out here we're

going to add the event

listeners so first we're going to select

all the delete links on the page using

document. query selector all brackets

and then a string and we're going to

select a class using Dot and the class

js- delete

daslink and then we're going to Loop

through all these links so dot for each

brackets and a

function and and in here it will give us

the link every time and then for each of

these links we're going to add an event

listener so

link.

addevent

listener

brackets and here we're going to give a

string and the event we want to listen

for which is a

click and then a function that we want

to run when we click these links so for

now let's just

console.log string delete to make sure

that it's working so we'll save

this and then in here we click these

delete links and then open the console

right click

inspect

console we can see that it's working now

so now let's go back to our

code so when we click delete we're going

to do two steps the first step is we're

going to remove the product from the

cart and the second step is we're also

going to update our HTML and remove the

product from the page so let's start

with the first step so when we click

delete how do we know which product we

need to remove from the

cart so we learned how to do this for

the added to cart button we can attach

the product's ID to the link element so

let's scroll up again to where the

delete link is which is right here and

we're going to attach the products ID to

this element using a data attribute so

at the end here we're going to add

data-

product-id equals double quotes and then

here we'll

substitute the matching

product. ID and

save and now that we attached the

product ID to this element we can get it

in our JavaScript below so let's scroll

down and then here we're going to delete

this line and using the link element we

can get that product ID using link. dat

set to access the data attributes and

we're going to access product

ID and let's save this in a variable so

we can use it later so const product ID

equals this

value and let's

console.log this to see if it

works and

save so now if we go to the project and

click the delete link for the first

product and then look at the console

inspect and console it will show us the

products

ID if we click the second products

delete link it will show us the second

products ID so now now we have the ID

that we need to remove from the cart so

now how do we actually do that so before

we begin figuring that out instead of

writing all the code down here let's

actually create a function inside C.J to

do this task the reason we're going to

do this is because cart. JS is supposed

to contain all the code that's related

to the cart so this will help us

organize our code better so let's open

our files again again and we're going to

open cart.

JS and we're going to scroll to the

bottom and we're going to create a

function for removing a product from the

cart so let's type function and let's

name it remove from cart brackets and

curly

brackets so this function we'll take a

product ID which we have and remove it

from the cart so here let's let's create

a parameter for the ID product ID and

now in here we're going to figure out

how to remove it so here's one way we

can do this first we can create a new

array and then we can Loop through our

cart and then add each product to the

new array except for this product ID so

now let's convert these steps into code

so inside this function here let's

create a new new array using const we'll

call it new cart equals an empty

array the next step is we're going to

Loop through our cart so we'll type

cart. for each brackets and a

function and we'll give it a parameter

cart item and the last step is that

we're going to add each card item to the

new array except if it has this product

ID so we can do that by checking if the

cart

item. product ID is not equal to the

product ID that we're looking for

product

ID so if it's not equal to the product

we're trying to remove we're going to

add it to the new cart so new cart. push

cart item

so the result of this Loop is it's going

to contain all the cart items that don't

match this product ID and that's the

same thing as removing this from the

cart so now the last step is we're going

to take our new cart and replace the

cart up here so we'll scroll

down and then here we'll make cart equal

to our new

cart because we're reassigning this

variable we have to scroll up and change

it from const to let and

save so now that we created this

function let's use it in our checkout

page first we're going to use the

modules feature and Export this function

and

save and then inside checkout. JS we're

going to import this function so I'm

just going to move this down to the

bottom so we can see it side by side

so here so in checkout. JS we're going

to scroll up and we're already importing

from cart. JS so we're just going to

import one additional Thing by typing

comma and we're going to import this

function remove from cart and

save and then we're going to use this

function at the bottom so we'll scroll

down and then here we're going to

remove from cart brackets and we're

going to give it the product ID we want

to remove so product

ID and lastly let's just console.log the

cart to make sure that this works so

console.log the card and

save so now let's go into our

project and we're going to click this

delete link for the first product so

delete and let's open the console right

click inspect the console and now it's

going to show us that we have one

product remaining in the cart and this

product has a quantity of one which is

the second product here so by clicking

that delete link We successfully removed

this product from the cart so now if we

refresh and tried clicking the second

delete

link and look at the

console and then EXP expand the cart it

will tell us that the remaining product

has a quantity of two which is this

product so we successfully removed the

second product from the cart when we

clicked

delete so now let's go into get and look

at our changes so we'll go into this

section well I can close this for now

and we'll open git and it will tell us

that in C.J we change it to let and we

created this new remove from cart

function and then in checkout. JS we

import that function and then at the

bottom when we click the delete link

we're going to remove this product from

the cart now finally we can remove this

console.log save and we're going to put

these changes into git so we'll type a

message to describe our

changes delete products from cart when

clicking

delete and

commit the second thing we have to do

when we click delete is to update our

HTML so if we go back to our

project when we click delete we want to

remove this product from the page so one

way we can do this is first we're going

to use the Dom to get the element we

want to remove and then we can use a

method called

remove so every element that we get from

the Dom has a method called remove which

removes it from the page so first of all

how do we know which element to get from

the page so let's actually look at the

HTML for one of these products we're

going to

rightclick

inspect and then click the top left and

then click one of these products

here and this will give us the HTML so

these two products are represented by

these two divs here with the class

cart--

container so one way to identify which

product this is for is to add a special

class to this element and this class

will contain the product

ID and then if we go back to our code

and we open checkout. JS and scroll to

the

bottom when we click delete we have the

product ID here so we can use this to

select that special class that we're

going to add so first let's add that

special class to each of these elements

so we're going to scroll up to the

HTML and we're going to go to the top

here to the div cart--

container and then here we'll add a

special class

js- cart Das item Das container Das and

then we'll substitute the product's ID

so we'll type the

matching

product.

ID and let's put this class on a

separate line so the line is not too

long now let's

save and now we're going to scroll to

the bottom and use our code to get this

class so we'll scroll to the

[Music]

bottom and here we're going to use the

Dom as well as this product ID to get

that special class that we just added

above so here we can type

document. query selector brackets and

then inside we'll type a string and

we'll select the class using a DOT js-

cart D item D container Dash and then

we're going to substitute the product ID

so because we want to insert something

in here we're going to switch this to a

template string using

backtick and now we can substitute this

product ID into this

string product

ID so by creating the string like this

we're able to select the specific

container that we need so now let's save

this in a variable so we can use it

later so const container equals this

result so for now let's let's actually

console.log this to see if it works

console.log

container and

save and then we'll go back to our

project so just move this

here and then in our project if we click

delete on the first product and then

check the console right click inspect

and the console you can see that we're

getting the correct element that we

should delete if we go out here and

click this delete link and check the

console you can see that this is also

getting us the correct element that we

want to

delete so now that we have the element

we want to delete the next step is to

use the do remove method so again every

element we get with the Dom has a method

called do remove which will remove it

from the page so if we go back into our

code down here all we have to do is type

out the element

container. remove and brackets and this

will remove it from the page if we

save and try it out so we'll go in here

we'll click delete on the first product

and it will remove it from the

page if we click delete on the second

product it will also remove it from the

page so that's it now let's refresh to

bring the products back

and that's how we make the delete link

interactive and remove the products from

the cart as well as from the

page so now let's save our changes into

git we'll go to the git

section and it will tell us that in

checkout. JS at the top we added that

special class which contains the product

ID and if we scroll down to the

bottom we created the string which will

get us these specific element that we

want to remove and then we use the do

remove method so now let's create a

message to describe our

changes delete products from

HTML when clicking delete and

commit the last thing we're going to do

in this lesson is we're going to add

local storage to our cart so if we go

back to our

project if we delete some products in

our cart and then

refresh notice that our cart goes back

to what it was before and that's because

right now if we look at our code and we

open cart.

JS our cart is just a variable and

variables are reset when we refresh the

page or when we go to a different page

so again if we go back to our project

and we go to a different Page by

clicking the top left so on this

homepage we can add as many products as

we want to our cart and if we go back to

the checkout page our cart will just get

reset to whatever it is here so that's a

problem with just using a variable to

save our cart it gets reset when we

refresh the page or we go to a different

page to solve this problem we're going

to use local storage to save our cart

so first let's create a function for

saving the cart to local storage because

we might want to reuse this code so down

here let's create a function we'll call

it save to storage brackets and curler

brackets and we're just going to save

the cart to local storage using local

storage do set item

brackets and set item takes two

strings the first string is the name of

whatever we want to save so we're going

to save our cart so we're just going to

call this the cart and then the second

string is the data that we want to save

so remember that local storage can only

save strings so to save our cart we need

to convert it into a string first and we

can do that using

json.

stringify brackets and then inside we're

going to give it the cart so this will

convert the cart into a string and now

we can save it in local storage so now

let's use this function whenever we

update the cart we need to save it to

local storage so it doesn't get reset

when we refresh the page so here when we

add it to the cart at the bottom after

we update the cart we're going to use

that function we created above save to

to storage and

brackets and also in the function remove

from cart so this function is also

updating the cart so after we update the

cart we're also going to save to storage

and brackets and

save so now whenever we update the cart

we're going to save it in local

storage the last thing we need to do is

at the top at the beginning of our code

we need to get the cart from local

storage instead of using this default

value so let's add some new lines here

to separate the code for a bit and here

we're going to get the cart from local

storage and we can do that using local

storage. get item and brackets so get

item takes one string and that is the

name of what we saved earlier which is

the cart so we're going to to give it

the string

cart so this will give us the cart that

we

saved however remember that local

storage can only save strings so it will

give us the string version of our cart

and we need to convert it back into an

array to convert it back to an array we

can use the code

json. pars and brackets and close

bracket the last thing we need to do is

when we first use the website we might

not have a cart in local storage so if

we don't have a cart saved local storage

will give us null so in this situation

if this value is null we want to give

the cart a default value which is this

value below so to give the cart a

default value if it's empty we can use

an if statement by typing if brackets

and curly brackets and then here we can

check if not

cart so if we don't have a cart in local

storage this will give us

null in this case not null will become

truthy and we're going to run the code

in this if

statement so if the cart is empty we're

going to make the cart equal this

default value below so let's just select

this code and we'll right click cut and

then in here right click and

paste and remove the extra line and

save so now if the cart is empty we just

give it a default value if we go back to

our project and try out our code so

let's delete the first product and

refresh the page notice that the cart

gets saved and the first product remains

deleted if we go to the homepage and we

add some new products

and then go to our

cart notice that our cart is saved

between pages so by using local storage

we can save our cart even when we

refresh the page or go between different

pages so that's all we're going to build

in this lesson so to clean up let's

delete all these products in the

cart and then go to the

homepage and we'll add back two socks

and one basketball which which is the

default value of the

cart let's go back to the checkout

page and now we're done with this part

of the page so finally let's save our

changes into git we'll go to the git

section and it will tell us that inside

cart. JS we're now loading the cart from

local storage when we open the page if

the cart doesn't exist we're going to

give it a default value and we created a

function to save the cart into local

store

stage so now let's add a message to

describe our

changes save cart in local storage and

commit and that's the end of this lesson

in this lesson we learned about modules

which is a better way to organize our

code we created the checkout page in our

final project we learned about HTML link

elements and radio selectors we made the

delete link interactive and we saved the

cart in local

storage here are some exercises to help

you practice what we learned in this

lesson e

in this lesson we're going to learn

about external libraries and we're going

to finish the checkout page in our final

project an external library is basically

just code that is outside of our

project so far we've only been using

Code that is inside our project like

these

files well a lot of developers write

JavaScript code and then put their code

on the internet and we can actually load

their code from the internet into our

project and use it we call this code an

external library because it's code that

is outside of our project Let's do an

example and load our first external

Library we're going to go to the video

description and we're going to click

this

link for the hello external Library

and it will open up a page that contains

JavaScript code so I actually wrote this

code myself and you'll notice that this

is just normal JavaScript code we create

a function called hello and it just

console.log hello so this is called an

external Library it's code that is

outside of our project so the cool thing

is we can actually load this code from

the internet into our project so let's

give that a try we're going to go to our

project and we're going to open

checkout.

HTML and we're going to scroll to the

bottom and above the script tag we're

going to add another script tag to load

some code so

script and we'll give it a source

attribute and then in here instead of

using a fth like we've done before we're

going to give this a a URL of a website

that contains JavaScript code so if we

go back to our

browser and here the URL of this page is

up here so we're just going to copy this

right click copy and then paste it into

our

code right click and

paste so now the computer will get all

the JavaScript code from this URL or

from this

page so it's going to get all the code

from this page and load it into our

project like normal code so let's save

and let's give this a

try so this code creates a function

called hello so let's try running this

hello function in our project we'll go

to checkout. JS and then scroll to the

top and then here let's just run the

function hello so hello and brackets and

Save

now if we go back to our

project go to the checkout page and

check the console right click inspect

and the console you'll see that it

displayed the message

hello so that's how an external Library

works it's just code that is outside of

our project and we can load this code

using a script tag like this we just

give it the URL of where this code is

located

so there's two things you might be

wondering about how come we put the

script tag at the top so generally we

load external libraries first and then

we can use the library in our own code

below and the second thing is how do you

put code on the internet like this to

learn this you can check out my video on

how to put a website on the internet

it'll show you how to put any file like

HTML CSS and JavaScript files onto a

website like this

this next let's talk about why we use

external libraries external libraries

let us share code instead of writing all

the code ourselves we can use code that

other people wrote and this helps us

save time and avoid duplicating work

right now we're loading a very simple

Library so let's load a more complex

library to show how we can save a lot of

time and work let's go back to our

project and go to the checkout

page here we have a section for choosing

a delivery option for this product and

you'll notice that each option has a

date so this is the date that the

product should be delivered by so the

way this works is that the cheapest

option here takes 7 days to deliver the

$4.99 option takes 3 days to deliver and

the

$9.99 option takes one day to deliver so

to get these dates here we need to do

three things first we need to somehow

get today's date in our JavaScript

number two we need to do calculations

with the date such as ADD seven days or

add 3 days and number three we need to

display the date in an easyto read

format like

this now we could try to figure out how

to do this ourselves by writing our own

code but this is going to be a lot of

work instead we can use an external

Library to help us work with dates so in

this project we're going to use an

external Library called DJs this is a

popular library that helps us work with

dates so first let's load DJs into our

project we're going to go to the video

description and we'll click this

link for the DJs external Library

and when the page opens you'll see a

bunch of random code here now you might

think that this is some special code but

this is actually just regular JavaScript

code that has been compressed so

basically all the extra spaces have been

removed and the variable names have been

shortened to one

letter we can press JavaScript code like

this because we need to load this code

from the internet into our project by

compressing it it makes this code

smaller so it will load into our project

faster so this compression process is

called minification or we Minify the

code okay so this is the code for the

external Library DJs now let's load this

code into our project we'll go back to

our

code and then go to checkout.

HTML and then here we're going to add

another script tag less than script and

the source

attribute and then here we're going to

give it the URL of the code we want to

load so let's go back to the code for

DJs and then up here we're going to

rightclick and copy this

URL and then inside our code in the

source attribute we're going to

rightclick and paste the

URL and

save so again this will take all the

code that's located on this page and

then load it into our

project now let's give it a try the DJs

external Library creates a function

called

DJs so we'll go to checkout. JS and then

at the top we're going to run the JJs

function and

brackets now make sure this is all

lowercase cuz that's the name that the

library used so now let's actually

console.log the result of this function

console.log

and

save and we'll go back to our project in

the checkout page we're going to check

our

console and you'll see that the DJs

function gives us an object and this

object represents the current date and

time so we know that DJs is working and

that's it we successfully loaded the DJs

external Library into our

project now let's learn how to use

DJs external libraries usually have a

documentation page that shows us how to

use the library we can find the

documentation Page by searching on

Google the library name like DJs and

then documentation or we can ask an AI

tool how to use the library to make

things easier in this video I'm going to

show you the features that we need and

you can go through the documentation

later if you want so earlier we said we

needed to do three things with the date

first we want to get today's date number

two we want to do calculations with the

date and number three we want to display

the date in an easyto read format DJs

helps us do all of these things so first

let's use DJs to get today's date

according to the documentation to get

the current date and time we can just

use the DJs function like

this so if we go back to our code

and that's what we have here we call DJs

and it gives us an object that

represents the current date and time the

second thing we need to do is to do

calculations with the date so for the

delivery options here we need to

calculate today's date plus 7 days or

today's date plus 3 days so again the

DJs Library can help us do

this so let's go back to our

console and look at the object that we

get back from DJs so this object

represents today's date and time and

this object also has a method called add

which adds a certain amount of time to

this date so this is what we need for

the project to calculate these dates

here let's go to our

code and first let's save this result in

a variable so we're going to remove this

and create a variable const today

equals

DJs and then down here we're going to

use the add method so we'll type

today. add and

brackets now the add method takes two

parameters the first one is the number

of time that we want to add so if we

want to add seven days we're going to

type seven and then the second parameter

is the length of time that we want to

add so if we want to add seven days

we're going to give it a string days so

this will add seven days to today's

date so let's save this result in a

variable const delivery date equals this

result and we'll console.log it to make

sure it's working correctly

console.log the delivery date and

save now if we go back to our project

and open the

console it will give us an object that

represents 7 days after to date or 7

days after when you're watching this

video so that's how we use DJs to do

calculations with the date it gives us

methods like add to add a certain amount

of time to the date finally we're going

to use DJs to display this date in an

easyto read format like

this so according to the document

this date object has another method

called format which will display the

date in an easyto read format so let's

go back to our

code and we'll remove the

console.log and we'll type delivery

date.

format and then inside these brackets

we're going to give this method a string

so this string tells DJs what kind kind

of format we want for the date so in the

documentation it has a table showing us

some special characters we can put into

this string for example if we want to

show the day of the week like Monday or

Tuesday we can type four D's into the

string and this will give us a string

where this text is replaced by the

actual day of the

week if we want to add a comma and a

space to this format we can just add a

comma and space and this will show up

directly in the result now let's say

that after this we want to show the

month according to the documentation to

show the month we can type for Capital

M's and it will replace this with the

month and finally we'll type a space and

according to the documentation if we

want to insert the day of the month into

the string we can type a capital D

so this method takes this date and

converts it into a string with this

format so now let's console.log this to

see what it looks like well

console.log and

brackets and

save and then go into our project and

open the

console and now you should see the date

7 days after today but displayed in an

easyto read format

so that's how we use the DJs external

library to help us work with dates and

as you can see it saves us a lot of time

and work we don't have to figure out how

to work with dates ourselves we can just

use someone else's code to solve this

problem so a best practice in

programming is when we need to do

something complicated try to find an

external Library first before writing

the code

ourselves to find external libraries we

can you can search in Google JavaScript

and then what kind of Library we're

looking for like date

Library we can also use an AI tool to

help us find external

libraries next we're going to learn how

to use external libraries and JavaScript

modules together right now if we look at

our code and go to checkout.

HTML we're loading these libraries using

script tags the problem with script tags

is that it runs this code directly on

the page and this might cause naming

conflicts for example the hello Library

creates a function called hello so if

something else is called hello in any of

our other code it might cause a naming

conflict a better way to load external

libraries is to use JavaScript modules

because a module will contain this code

inside a file and any variables that are

created inside inside the file will not

conflict with anything outside of the

file to use external libraries and

JavaScript modules together we're going

to use a special version of the library

called an esm version esm stands for

ecmascript modules ecmascript is just

another name for JavaScript so the esm

version of a library is just a version

that works with JavaScript

modules so let's do an example we're

going to go to the video description and

we're going to open the esm version of

hello.js so you can see that it's the

exact same code as before we're creating

a function called hello except this time

I just added the word export in front of

function so this turns the library into

an esm version and now it will work with

JavaScript modules so let's use the esm

version in our code we're going to go

back to our

code and we're not going to use script

tags to load this anymore so let's

delete

this and

save and then in checkout. JS at the top

we're going to use an import to import

this function into our code so we'll

type import curly brackets we'll import

the function

hello and we're going to import it from

a string and then this time instead of

giving it a file path like before we're

going to give it a URL that contains our

code so on the web page we're going to

rightclick and copy the URL at the top

and then inside our code in here we're

going to rightclick and

paste so this import works the same way

as before before except now the codee is

coming from the internet rather than one

of our files so let's

save and then go back to our project and

check the

console and you can see that everything

is still

working so that's how we use external

libraries and JavaScript modules

together we just load the esm version of

the library and we use import as normal

except this time we're importing from

code that is on the

internet next let's use DJs with

JavaScript modules to do that we're

going to load the esm version of DJs so

we're going to go to the video

description and click this link for the

DJs esm

version and now we're going to load this

code into our project so let's go back

into our codee and first let's open

checkout.

HTML and we're going to remove this

script tag because we're going to load

this with JavaScript modules so let's

save and then go into checkout. JS and

then at the top we're going to import

from the DJs esm version so we'll

import and we're going to use a slightly

different syntax we're just going to

type

DJs without the curly brackets and then

we'll type from a

string and we're going to give it the

URL that contains the code so we'll go

to our

browser and then click the URL at the

top we're going to right click

copy and then in our code inside these

quotes rightclick and

paste and

save so now let's open our project and

take a look at the the console to make

sure it works so we'll right click

inspect the

console and everything is still working

so that's how we use the DJs external

library with JavaScript modules so

before we continue we're going to learn

about this new syntax that we used here

so this syntax is called a default

export a default export is another way

of exporting something from a file we

can use it when we only want to export

one thing from a file and it makes the

syntax a little bit cleaner because we

don't have to type the curly brackets so

let's do an example of a default export

to see how it works we're going to open

the utils folder and open money.

JS and at the bottom we're going to

create a default export by typing

export default and then whatever we want

to export so let's say we want to export

this function here so we just type the

name of the function format

currency and

save and now when we import this we can

just import the name without the curly

brackets so the syntax is a little bit

cleaner now each file can only have one

default export so if we only want to

export one thing from a file this is

another syntax that we can

use so some people like using default

exports because they feel that exporting

only one thing from a file makes the

code cleaner however in your own code

it's up to you which version of export

you want to

use let's go back to checkout.

JS and then here the DJs Library only

exports one thing which is the DJs

function so they chose to use a default

export instead of a normal export that

we were using before

by the way the syntax up here with the

curly brackets is called a named

export so when we use external libraries

in the future some libraries will use

named exports like this and other

libraries will use a default export like

this so it's useful to know both

syntaxes so that's how we use external

libraries and JavaScript modules

together we just import from the esm

version of the library now keep in mind

that not every library has an esm

version so for some libraries we still

have to use a script

tag okay now that we learned external

libraries let's do some practical

examples we're going to go back to the

checkout page and we're going to use DJs

to create the delivery options here so

the way this works is that we can select

one of three delivery options when we

click an option it should change the

delivery date up here and it should

change the prices on the right side so

let's get started as always we're going

to do three steps first we're going to

save the data and then we're going to

generate the HTML and finally we're

going to make it interactive so first

what data do we need to save for this

section well each delivery option has a

delivery time like 7 days or 3 days and

each option also has a

price so right now here's what our cart

looks like now we could save the

delivery option details inside the cart

like this however notice that this data

gets duplicated for each product in the

cart instead we're going to save the

delivery options

separately and then just save an ID that

points to the delivery

option as a reminder this technique is

called normalizing the data we save the

delivery options separately and then we

just save an ID

that points to the full delivery

option so let's create the data for the

delivery options we'll go into our code

and then in the data folder let's create

a new file for this and we're going to

name this file delivery options. JS and

press

enter and in here we'll create a list of

delivery options that we can pick from

we'll create a variable const delivery

options equals and array because we want

a list and then each delivery option is

going to have multiple values like the

time to deliver as well as the price so

we're going to make each of them an

object to group these values together so

I'm going to rearrange my windows here

so that we can see the data that we're

trying to save and we can actually close

these tabs for now

so here let's save the data for the

first delivery

option first let's give it an ID

property because as we mentioned we're

going to save the ID in the cart and

then we're going to use that ID to get

the full delivery option here so to keep

things simple let's just give it a

string and an ID of

one and then we're going to give it

another property and we're going to save

the delivery time so for the first

option it's going to take seven days to

deliver so let's create a property

delivery days colon 7 and comma and

we're also going to save the price so

this one is free so we're going to save

the price cents and zero remember that a

best practice when calculating money is

to save it in

cents and next let's save the data for

the second delivery option here we'll

type a comma and another object and

let's give it an ID of two this time and

this one is going to take three days to

deliver so we'll type delivery days

colon 3 and we'll give it a price cents

and this one is

$4.99 so

$4.99 and then finally we're going to

save the data for the third delivery

option comma another object ID of three

and this one is going to take one day to

deliver so we'll type delivery days

colon 1 comma and the price sense is

$9.99 so price sense 999 and

save so now that we've created our

delivery options for each product in the

cart we're going to save the ID of the

delivery option that's selected so for

example here we selected the first First

Option we're going to save an ID of one

in our cart so let's go back into our

code and we're going to open the

cart so here in the default cart we're

going to save the delivery option ID

colon and let's say that the first

product selected the first delivery

option so we're going to save the ID one

and then for the second product we're

also going to save a delivery option ID

colon and then let's say that for the

second product we chose the second

delivery option here so here we're going

to give it an ID of

two next when we add a product to the

cart we also need to give it a delivery

option ID so if we scroll down to the

add to cart function here we're adding a

product to the cart so when we add a new

product we also want to give it a

delivery option ID so we'll type

delivery option ID colon and for new

products let's give it a default

delivery option of one so for new

products to select the first one and now

let's

save and lastly we might have a cart

that is saved in local storage so we'll

need to add the delivery option ID to

local storage as well but to keep things

simple let's just do a shortcut we're

going to delete the cart in local

storage and then it will go back to

using this default value which has the

delivery option

IDs so to delete the cart from local

storage we're going to go into our page

and open the console right click

inspect the

console and we're going to type local

storage. remove item brackets and the

cart and press

enter so this will erase the cart from

local storage and it will use those

default values so now let's go to our

page and

refresh and it should be using the

default cart so that's how we save the

data for the delivery

options by the way in the rest of this

course if you get an error in your

project but your code looks correct you

may have some bad data saved in local

storage to fix this you can try running

local storage. CLE in your console to

remove everything from local

storage and then refresh the

page the next step is to generate the

HTML first let's find the HTML for the

delivery options here to do that we can

rightclick this part of the page and

inspect

and this will give us the HTML for this

part so we're going to find the element

that represents this part of the page

and that's this one right here it's a

div with the class delivery Das options

and to find this in our code we're going

to search for this class so let's go

back to our

code and then we're going to open

checkout. JS which is right

here and we'll press crlf or command F

to find code and we're going to look for

the class delivery Das

options and it will give us this code

right here so this is the HTML for the

delivery

options so now instead of writing this

HTML directly we're going to generate

this with

JavaScript to keep our code organized

let's create a function for generating

this

HTML we'll scroll to the

bottom and then here we'll create a

function and let's call it delivery

options

HTML brackets and curly

brackets and now inside here we're going

to do three steps first we're going to

Loop through the delivery options we

created earlier and then for each option

we're going to generate some HTML and

then finally we're going to combine all

the HTML together so first let's import

the delivery options at the top so we'll

scroll up and we're going to

import curly brackets from quotes and

we're going to locate the delivery

options file which is inside the data

folder so first we need to get out of

the scripts folder we'll type dot do

slash and then go into the data folder

slash delivery options. JS and we're

going to import the delivery

options now one thing I forgot to do is

that inside these delivery options we

need to make sure that we export this

variable so we're going to type export

and

save and we'll go back to checkout. JS

and then here we're going to Loop

through the delivery options below so

we'll scroll back

down to this new

function and type delivery options. for

each brackets and a function

inside and we'll name the parameter

delivery

option so for each delivery option we're

going to generate some HTML so let's use

a template string to save the

HTML and then we're going to scroll up

and we're going to find the class

delivery Das option so this is the HTML

for one delivery option so we're just

going to copy this HTML into our Java

JavaScript below so we'll right click

copy and then down here inside the

string give some new lines and

rightclick and

paste and if we need to reformat we can

select these lines and press

tab okay now when we're generating the

HTML instead of using the same date

every time we're going to calculate the

date using DJs and then insert it into

here to calculate the date we're going

to get today's date first using

DJs so up here let's create a variable

const today

equals and according to the

documentation to get today's date we can

just call the DJs function so we'll type

DJs and

brackets next

each delivery option takes a certain

amount of days to deliver so we need to

add that to today's date to do that we

have a method called add So Below this

let's create a variable to save the

result const delivery date

equals

today. add

brackets and we're going to give it two

parameters the first parameter is how

many dat days we want to add and this is

saved in the delivery option so here

we'll give it the delivery option dot

delivery days

comma and then we'll give it the length

of time we want to add which is a string

days now that we calculated the correct

delivery date we need to display it in

an easyto read format and again DJs has

a method called format that Let's us do

this so below let's create a variable

const and we'll call it date string and

make it equal to delivery

date.

format brackets and will give it a

string so the format we want is we want

to insert the day of the week so

according to the documentation we can

use

4ds and then a comma and a space and

then we want to insert the month and

according to the documentation that's 4

Capital

M's and finally we're going to insert

the day of month which is capital

D so now that we calculated this date

string we're going to insert it into the

HTML instead of using the same date

every time so we'll remove this and then

insert the date

string next let's insert the price

because it's going to be different

prices every time so at the

top let's create a variable const and

we'll call it price string and make it

equals and remember each delivery option

has a property price sense so if the

price ense is zero we want to display

the text free if the price sense is not

zero we want to display the price as

dollars with a

dash so to do that let's practice using

a Turner operator so first we'll check

if the price sense is zero so we'll type

delivery option. price sense is triple

equals to

Z and then we'll type a new line and

question mark and also a new line and

colon so remember the way that a Turner

operator works is that if the first part

returns true the value is whatever is

after this question Mark if the first

part is false then the value is whatever

is after the colon so it's sort of like

an if statement except we can save the

result in a

variable so if the price sense is zero

that means it's free so we want to

display the text free so we'll create a

string

free and if the price sense is not zero

we want to display the price as dollars

so here we're going to type a template

string a dollar sign and we're going to

insert the price sents as

dollars so here we'll type delivery

option. price sense and to display this

as dollars we already have a function

for this called format currency so at

the front we're just going to type

format

currency Open Bracket and close

bracket and then at the end let's add a

dash so here we'll add space and dash

and

semicolon so that's how we create the

price string for each delivery option so

now let's substitute this into the HTML

so we'll remove this and substitute the

price string and

save so now instead of using these same

values every time we're substituting the

values in into the

HTML finally let's combine all this HTML

together so we're going to scroll up to

the top and outside of this loop we're

going to create a variable to save the

result so let HTML equals empty string

to start and then every time we Loop

through we're going to add this HTML to

this result so here we're going to type

HTML plus

equals and finally after we've created

this HTML we're going to return it from

this function so at the bottom we're

just going to return the

HTML and

save now that we generated the HTML for

the delivery options let's insert this

into the HTML

above so instead of creating this HTML

directly we're going to delete it

and then here we're going to insert and

we're going to run this function to

generate it so here we're going to type

delivery options HTML and

brackets now before we save one thing

that we're missing in this function is

that if we scroll down here we're using

a variable called matching product but

this variable is not accessible inside

this function so let's actually pass the

matching product into here so at the top

we're going to add a parameter matching

product and then when we call this

function up here we're going to pass in

the matching product so matching product

so now let's

save and check our page and now we're

generating the HTML for these delivery

options and you'll notice that your

delivery dates here will be based on

today's date or when you're watching

this video so this will be 7 days after

today or 7 days after when you're

watching this video this will be 3 days

after today or 3 days after when you're

watching this video and this will be one

day after

today now one thing we need to fix here

is that these selectors are empty

however we want the delivery option that

is saved in the cart to be checked to do

that let's go back to our

code and in order to make one of these

selectors selected we're going to scroll

down to the input

element and we're going to add an

attribute called

checked and this attribute makes a

selector

checked however we don't want all of

these delivery options to be checked we

only want it to be checked if it matches

the delivery option ID that is saved in

the cart so let's write some code up

here to figure out which delivery option

should be checked we're going to create

a variable const is

checked

equals and we only want it to be checked

if this delivery options ID matches the

delivery option ID in the cart so we'll

test if delivery option. ID is equal to

the cart item

do delivery option

ID now inside this function we actually

don't have access to cart item so let's

actually pass it in as a parameter cart

item up here and then when we call the

function this outer function has access

to the cart item so we're going to give

it the cart item so we're going to put

it into this function and then we can

use it down here

so now that we have this

variable instead of being checked all

the time we're going to remove this and

insert and we're going to use a tary

operator here is

checked question mark and colon so we

can also use a ternary operator when

we're inserting into a string so again

if this is true it's going to get the

value after the question mark So if it

is checked we're going to give it the

value

checked if this is false we're going to

give it the value of empty string so

it's the same thing as if this attribute

didn't exist so now if we

save you'll notice that the correct

delivery option is checked for each

product the first product we saved

delivery option one and the second

product we say delivery option

two finally let's replace this date at

the top with the delivery date that we

selected

here we'll go back to our

code and we'll scroll to the

top until we see this date in our code

here so now we're going to calculate

this date using the delivery option that

we picked so remember that inside the

cart we only saved the delivery option

ID so let's use this to get the full

delivery

option so at the top here let's get the

delivery option ID out of the cart const

delivery option ID equals cart item.

delivery option

ID next we're going to use this ID to

find the full delivery option now we did

something similar with the product ID we

Loop through the products found a

matching ID and then saved it in a

variable up here so we'll do the same

let's create a variable to store the

result let

delivery option and then we're going to

Loop through the delivery options so

delivery options. for each brackets and

a

function and let's name the parameter

option because we use the name delivery

option up here so in here we're going to

look for a matching ID so if this option

ID is equal to the delivery option ID

here we're going to save this inside

this variable so delivery option equals

option so now we have the full delivery

option in our code and we can use it to

get the delivery days property and then

calculate the day that we need

here to calculate this state we already

wrote some code for this at the bottom

if we scroll down in our

code when we created the delivery

options we calculated the date for each

delivery option so we can reuse this

code above so let's select this code and

then right

click

copy and then at the

top after we get the delivery option

we're just going to rightclick and paste

that code again

and if we need to we can reformat by

selecting these lines and press shift

tab so this code will take the delivery

option that we selected and calculate

the delivery date that we need to show

down here and now instead of using the

same date every time we're going to

remove this and insert the date string

that we created Above So date string and

save so now this date string up here

will match the delivery date that we

chose on the right side so that's how we

generate the HTML for the delivery

options using the DJs external Library

so now let's take a look at our changes

in git we'll go to our code and open the

git

section and here it'll tell us in cart.

JS we added delivery option IDs to the

cart

as well as when we add to the

cart and then in this file we created

the list of delivery

options and in checkout. JS instead of

writing this HTML directly we generated

it and then in money. JS we learned

about default exports so let's type a

message to describe our changes save

data and generate HTML for for delivery

options and

commit the last step is to make it

interactive so when we click a delivery

option we need to do two things first we

need to update the delivery option ID in

the cart array and number two we need to

update the page so we need to update

this date here to match the date that we

select

let's start with the first step let's

create a function for updating the

delivery option in the cart we're going

to go to our

code and we're going to open the file

called cart.

JS so because we're modifying the cart a

best practice is to put the code inside

this file this file should contain all

the code that manages the cart so we're

going to scroll down to the bottom and

we're going to add a new function so

let's type function and let's name it

update

delivery option brackets and curly

brackets so when we update a delivery

option we need to know the product that

we want to update as well as the

delivery option that we chose so we're

going to need two things for this

function the product ID and the delivery

option

ID so the steps to do this is first

we're going to Loop through the cart and

find the product and then we're going to

update the delivery option ID of that

product so to find the product using the

product ID we already have some code for

this if we scroll up to the add to cart

function we have this code which takes a

product ID and finds the matching

product in the cart so let's just make a

copy of this code we're going to select

it right click

copy and then paste it into our new

function so down here right click and

paste so this will give us the card item

that matches this product ID and save it

in this

variable next each card item has a

property called delivery option ID so

we're just going to update that property

so down here we can just type the code

matching item. delivery op option ID and

make it equal to the delivery option ID

that we give to this function so

delivery option

ID and lastly because we updated the

cart we should save it to local

storage so we can use this function we

created earlier save to

storage and brackets now let's

save now that we have this function

let's use it on the checkout page so

first let's export it so we can use this

in another file we're going to export

this

function and

save and then open checkout.

JS and then in our project we need to

add event listeners to each of these

delivery options so we run some code

when we click them so inside our code

here we're going to scroll to the HTML

for each delivery option which is right

here and then we're going to add a class

so we can select it using the Dom js-

delivery D option and then we'll add an

event listener to these so we'll scroll

down and down here we'll add the event

listener using

document. query selector all brackets

and a string will'll select that class

we just created using dot js- delivery D

option

and then dot for each brackets and a

function so for each option we're going

to add an event listener and listen for

clicks so let's just call each of the

options an

element so for each of these elements

we're going to element.

addevent listener brackets and we're

going to listen for clicks comma and

we're going to run this function when we

click

it so as we said the first thing we'll

do is to update the delivery option ID

in the cart so now let's import that

function that we created earlier we're

going to scroll to the

top and we're already importing from the

cart so to import something else we're

going to add a comma and we're going to

import that function update delivery

option so now let's scroll back down and

use use it in our

code so here when we click a delivery

option we're going to update delivery

option brackets now we said we need to

give this function two things the

product ID that we want to updated for

as well as the delivery option ID that

we picked but how do we get these two

values and the answer is if we scroll

up here here we have access to the

product ID and we also have access to

the delivery option

ID so we can use data attributes to

attach it to this element

here so let's create a data attribute

data-

product-id equals double quotes and

insert the product ID which is matching

product. ID and we're also going to use

a data attribute for the delivery option

data- delivery D option- ID equals

double

quotes and we're going to insert the

delivery option here so delivery

option. and

save next let's scroll back

down and then here we're going to get

those values out of the the data

attributes by using const and let's use

the shorthand property here for practice

curly brackets equals the element. data

set and then out of the data attributes

we're going to get the product ID comma

as well as the delivery option

ID as a reminder this is a shorthand

property it does the same thing as the

code down here but it's just a

shortcut now let's

save and try out the project we'll go

back and here if we click the second

delivery option and then refresh the

page you'll notice that now this one is

checked and the date here is

correct so that's how we make the

section interactive we just update the

cart and then when we refresh the page

it will regenerate the HTML based on the

new cart

now let's save our code into git we'll

go back and open the git

section and then it will tell us in

cart. JS we added this function for

updating the delivery

option and in checkout. JS we imported

that function and then at the bottom we

added some event listeners and data

attributes and we use that function to

update the

card now let's add a message describe

describing our changes make delivery

options

interactive and

commit next when we select a delivery

option we need to update the

page so right now in our project when we

click a delivery option we need to

refresh the page for the text to be

updated so what we're going to work on

now is when we click this we want the

page to update

immediately so far in this course the

way we solve this problem is once we

click this we're going to use a Dom to

get this element here and then update

the text

directly however the problem with this

approach is that we need to update the

page one by one and later there might be

lots of places on the page that we need

to update for example when we change a

delivery option we also need to change

the numbers here on the right so there's

potentially a lot of things that we need

to update one by one and it's easy to

make a mistake or forget something so

now we're going to learn a better way to

update the page we'll go back to our

code and let's open checkout. JS

again and notice if we scroll

up here we already have all of this code

that takes our data and generates the

HTML so another way to update the page

is after we update our data we just need

to rerun all this code and regenerate

all this HTML so let's give this a try

first we're going to put all of this

code inside a function so we can rerun

it we're going to scroll to the

top and let's put this in a function by

typing function and let's call call it

render order summary brackets and curly

brackets so the word render just means

to display on the

page and we're going to call this

section the order

summary so this function should display

the order summary on the page next we're

going to put all of this code inside our

new function so let's just remove this

curly bracket

here and let's actually select all of

this code and we're just going to

reformat it by pressing Tab and adding

an indent and then at the end we're

going to add back that closed curly

bracket to finish the

function so all we did was we put all of

our code inside a

function and then at the bottom let's

run this function because we still need

to run all this code at the start of our

page so we're going to type render the

order summary

and brackets so this shouldn't change

anything because we're just running the

same code but now it's just in a

function let's save and

check and everything's still working so

that's good so now let's go back into

our

code and this time to update the page

instead of using the Dom to update the

page directly like we did up here we're

just going to rerun all of this code and

regenerate all the HTML

so after we update the data we're going

to rerun the code using render order

summary and

brackets now let's

save and try it

out so here let's say we start off with

the first delivery option if we click

the third delivery option you'll notice

that the date up here updates

automatically if we click the second

delivery option it updates automatically

as well

so that's a better way to keep the page

up to dat instead of using the Dom and

changing the HTML directly one by one we

just update the data and then regenerate

all of this

HTML so let's go back into our code and

there's two things that I want to point

out here so notice that we put our event

listeners into this big function and

that's because when we're regenerating

all the HTML we're essentially deleting

the previous HTML and replacing it so we

need to add the event listeners again

and the second thing I want to point out

is that inside the render order summary

function we can call render order

summary

again so a function can actually call

itself or rerun itself and this feature

is called recursion it's useful when a

function needs to rerun all of its code

so now let's save our changes into git

we'll open the git section and it will

tell us in checkout. JS we basically

moved all of our code into this function

and then at the bottom we call the

function at the start of the page and we

also call the function when we select a

delivery option so now let's add a

message describing our

changes

regenerate

HTML when updating

delivery option and

commit so the technique we just used

where we update the data and then

regenerate all the HTML this technique

is called

MVC MVC stands for model view controller

and is a popular technique in software

engineering in MVC we split our code

into three parts the first part is the

model this is all the code that saves

and manages the

data so in our project all the code in

this data folder is called the model

because this code saves and manages our

data the second part of MVC is the view

this is code that takes the data and

displays it on the page so in our

project if we open checkout. JS and

scroll to the top here we have code that

takes our data and then generates all

the HTML so this code is called the

view the last part of MVC is the

controller so this runs some code when

we interact with the

page so in our project at the

bottom these event listeners here would

be called the controller because they do

something when we interact with the page

or with the

view so in MVC we divide our code Lo

into these three parts and then they

interact with each other in a

loop first we use the model to generate

the

view so in our code that's what we did

here we took the model or the data which

is our cart and then we generated the

HTML or the view then when we interact

with the view it will run the

controller so that's what we did at the

bottom here

when we interact with the page we run

some

code then the controller will update the

model so that's what we did here inside

the controller we just updated our data

using this

function and finally we use the updated

model to regenerate The

View so that's what this code does it

takes the updated data and then

regenerates all the HTM ml or

regenerates The

View so that's how MVC Works instead of

updating the page directly with the Dom

we just update our data and then

regenerate all the

HTML so we use MVC because doing this

makes sure that the page always matches

the

data so MVC is known as a design pattern

it's a way to organize and design our

code in the future you might use a

technology called a JavaScript framework

to build websites many JavaScript

Frameworks are based on MVC so it's

useful to know how it

works okay now that we learned the MVC

design pattern let's do some practical

examples using

MBC we're going to open our project

again to the checkout page and we're

going to create this payment section on

the right now before we start if we look

at our code in this checkout. JS file

you'll notice that we already have a lot

of code

here instead of adding even more code to

this file let's actually split this up

into two different

files so one file will be responsible

for this left section and then one file

will be responsible for this right

section we're doing this to keep our

code more organized and so that we don't

have too much code in one file

so let's go back and let's create two

new files for the checkout page so up

here we'll create a file and let's call

this one the order summary. JS and press

enter and let's create another file for

the right section and let's call this

one the payment

summary. JS and press

enter now both of these files are

related to the checkout page so let's

create a folder and group them together

we'll create a new folder up here and

let's call it checkout and press enter

and we're going to move these two files

into this new folder so we move that and

we'll move

that next let's open checkout. JS and

let's move all of this code into the

order summary so we'll press control a

or command a to select all the code and

then

rightclick

cut and then in here we're going to

rightclick and

paste now there's a few things that we

need to fix here so first our checkout.

HTML file is still loading checkout. JS

so we actually need to run this function

inside checkout. JS instead of inside

here so let's actually remove

this and save and we're going to scroll

to the

top and let's export this function so we

can run it inside here so we'll type

export and save and then inside checkout

we're going to import curly brackets the

render order summary

function from a string and to locate

this file we're going to type A do slir

that means to start from the current

folder and we'll go into the checkout

folder checkout SL orderers

summary.

JS and finally we're going to run this

function when we load the page so render

order summary and brackets and

save another thing we need to fix is if

we open order summary .js we moved this

file into a folder so now all of these

file paths need to be updated do do

slash is now inside the scripts folder

and we can't find a data folder anymore

so this is going to cause an error so to

find the data folder we need to get out

of the checkout folder and then we need

to get out of the scripts folder so we

need to get out of two folders so we'll

just add an additional do dot slash and

then same thing for this we'll add

another dot dot slash and for the utils

now we need to get out of the checkout

folder and then into the utils folder so

we'll change this to do/

utils and then for here we're going to

go out an additional folder so another

dot dot slash and

save so now let's check if this still

works we'll go to our project and

refresh and try it

out and the p still works because we're

still running all of the same code but

we just organized it into its own file

so now let's open git and save our

changes so it's going to tell us that in

here we removed all this code and then

we separated it into the order summary

file and the payment summary file which

we're going to work on next so let's

type a message describing our changes

move order

summary into its own own file and

commit now let's start creating the

payment summary on the right side so in

our code let's open payment summary.

JS and just like the order summary let's

put all our code in a function so we can

regenerate the HTML if we need to so

we'll type function and let's call it

render payment summary brackets and

curly

brackets and let's just

console.log string payment summary just

to make sure it's working so we'll save

and let's export this function and then

run it inside checkout. JS so export

save and then in checkout. JS at the top

we're going to import curly brackets the

render payment summary function from a

string the current folder go into the

checkout folder and the payment summary.

JS file and then at the bottom we're

going to run the function so render

payment summary brackets and

save let's go back to our project and

open the console rightclick inspect the

console and we'll see the message

payment summary so now we know that our

code here is working and the export is

working

correctly now let's remove this code and

actually build the payment

summary as always we're going to do

three steps save the data generate the

HTML and make it interactive so let's

start with saving the data in MVC this

is called the

model so if we go to our

project for this section the data that

we need is just to calculate these

numbers

here so let's start by calculating this

first number here which is the cost of

the products to calculate this we can

Loop through the cart and for each

product in the cart we can multiply the

products price times the quantity and

then add everything together now let's

convert these steps into code we'll go

to our project and inside the payment

summary

file first we need to get the cart so

let's import it import curly brackets

the

cart from the string and we'll locate

cart.

JS so first we'll go out of the checkout

folder do do slash and then go out of

the scripts folder do do slash and then

into the data folder

data.js and

save and now we're going to Loop through

the cart so we can type cart. for each

brackets and a

function and let's name the parameter

cart item so for each cart item we have

the product ID and the quantity so we

need to multiply the product's price

times the quantity so first we need to

use the product ID and get the full

product details and we already have some

code for this inside orders summary. JS

if we scroll down here we have some code

that takes a product ID and finds the

matching

product now instead of copy and pasting

this code let's actually put this into a

function so we can reuse this and we'll

practice some modules so let's select

this code and rightclick and copy it

first and then let's go into the

products. JS

file and at the top we're going to

create a function so we can reuse that

code so let's type function and let's

name it get product brackets and curer

brackets and we're going to give this

function the product ID that we're

looking for and then let's paste the

code we copied earlier right click and

paste so this finds the matching product

using the product ID and then at the end

of the function let's return the

matching product so we can use this

outside of the function so now let's

export this function so we can share it

across files so export and

save first we'll go to the order summary

and at the top let's import that

function so we're already importing from

product .js we're going to import

something else using a comma the get

product function and then down

here instead of all this

code we're going to run that function so

we make this equal to get product and

run the function and we need to give the

function the product ID so let's just

give that here product

ID and because we're no longer updating

this variable we can change from let to

const and

save let's go to our project to make

sure everything's still working so that

looks

good and now let's use this function

inside payment summary. JS so the same

thing we will import curly brackets the

get product function from a

string and we'll go to the data folder

do SL do do SL data SL

and products.

JS and let's run that function to get

the full product so get product brackets

and then each cart item has the product

ID so we're going to give it to the

function cart item. product

ID and let's save this product in a

variable so we can use it for our

calculations con product equals get

product so now now as we said we're

going to multiply the product's price by

the quantity so down here we can do

product and it has a property

called price sense and we're going to

multiply it by the cart item and this

has a property do

quantity and the last step is to add all

of these

together so outside of the loop let's

create a variable to save the result of

adding them together let's type let and

we'll name it product price sense equals

and we'll make it zero to start and then

every time we Loop through the cart

we're going to add this to this variable

so we'll type product price sense plus

equals this value

here and that's how we calculate the

cost of the products so at the bottom

let's

console.log the product price sense just

to make sure that this is working we'll

save and in our project we're going to

check the

console and it will give us this number

here and this number should match the

number on the page except it's in sense

and assuming you also have two socks and

one basketball in your

cart okay so that's how we calculate

this first number here now let's

calculate the second number which is the

cost of shipping so to calculate this

we're going to Loop through the cart and

add all the shipping costs

together so let's go into our

code and here we're already looping

through the cart so instead of creating

another loop let's just calculate the

shipping cost in the same Loop so let's

create some new

lines and each card item has a property

delivery option ID so we need to use

this ID to get the full delivery option

which has the price so in the order

summary we also have this code that

takes the delivery option ID and finds

the full delivery option so again let's

create a function to share and reuse

this

code so first let's select this code and

we'll write click and

copy and let's go to the delivery

options. Js

file and then at the bottom we'll create

a

function let's call it get delivery

option brackets and curly brackets and

we'll give this function the delivery

option

ID and inside here we'll rightclick and

paste the code that we copied earlier so

this will take this ID and get the

delivery option from this array and

let's return return this delivery

option so we can use it outside of this

function and just to be safe let's also

give this a default value if we don't

find a delivery option so we'll use the

default operator

or and let's make the default value the

first delivery option so delivery

options square bracket 0

so now let's export this and

save and then inside order summary we'll

use this function so at the

top we're already importing from

delivery options so we'll type a comma

and get delivery

option and then down here instead of

running all this code we'll select it

and make this equal and run the function

get delivery option

brackets and we'll give it this delivery

option ID delivery option

ID and we can change from let to const

since we're not changing this variable

so now let's save and let's use this

function inside payment summary as well

so in here at the top we'll import curly

brackets the get delivery option

function from

quotes the data folder do do slash do

data slash and the delivery options. JS

file and now we'll run this function get

delivery option and

brackets and each cart item has a

delivery option ID so we'll put that

into the function cart item. delivery

option

ID and let's save this in a

variable con delivery option

equals and now we can get the price for

the delivery option using delivery

option price sense

property and finally we're going to add

all these together so at the top let's

create a variable to save the result let

we'll call it ship

shipping price cents equals zero and

when we Loop through the cart we're

going to

do shipping price sents plus equals this

delivery options

price and let's also console.log this to

make sure it's working so shipping price

cents and Save

now let's go to our project and check

the

console and this value

here should be the same as adding these

two numbers together in

sense so that's how we calculate the

second number the shipping price so note

that this

$4.99 number is just a practice number

right now the actual shipping price

should be the total of adding all these

sh shipping prices

together the next number we need to

calculate is the total before tax so let

just adding these two numbers together

inside our

code let's remove these console. logs

and we'll create const total before tax

sense and make it equal and we'll add

these two together product price sense

Plus shipping price

sense and the next number is the tax so

we're going to calculate a 10% tax on

this number here to calculate 10% of

something we can multiply this by 10 /

100 that's what percent means so 10 ID

100 is also equal to

0.1 so we can also multiply this number

by

0.1 let's go into code and we'll create

a variable const tax sense make it equal

to the total before tax sense times 0.1

or

10% finally to calculate the total we're

going to add these two numbers together

so const total sense equals the total

before tax sense Plus the tax

sense so that's how we calculate all the

numbers in the payment summary and now

we have all the data that we need next

we're going to generate the HTML in MVC

this is called The

View so at the bottom here let's create

a variable to store the

HTML const payment summary

HTML and we'll make make it equal to a

template

string and then inside here we're going

to copy and paste the

HTML so let's open checkout.

HTML and we're going to scroll up until

we find the class payment D summary so

we're going to generate all the HTML

inside here so let's actually select

this HTML and move it into our

JavaScript so we'll select it up until

this button and then we we can

rightclick

cut and remove the new line save and

then inside the payment summary inside

the screen we'll rightclick and paste

the

HTML and if we need to reformat we can

select these

lines and press tab a few times to

reformat

it and and

save next instead of using these same

numbers every time we're going to take

the numbers we calculated up here and

insert it into this HTML string so

instead of 42.75 every time we're going

to insert the product price

sense and let's give it some new lines

to make it a little easier to

read now remember that this number is in

sense and we want to display it as

dollars to do that we already have a

function for this so in the utils money.

JS file we have a function format

currency that displays it in dollars so

let's use this function inside payment

summary so at the top let's import the

function

first import curly brackets the format

currency function from a Str

and to locate this folder we'll go out

of the checkout folder do do/ the UIL

folder SL money.jpg

numbers here so this one is the shipping

price so we can

insert format currency brackets the

shipping price sents and let's give it

some new lines to make it a little

easier to

read next let's insert the total before

tax so we'll remove this number and

insert format currency bracket gets the

total before tax

sents and new

lines and next is the tax we'll remove

this and

insert format currency brackets the tax

sents and we'll enter some new lines and

finally the total so we remove this

insert

format currency brackets total sense and

add some new

lines and

save now before we continue I actually

learned of a small issue with the format

currency function so let's open the

money. JS

file and I recently learned that this

two fixed method has a small issue with

rounding so for some numbers that end in

five it won't round the number

properly one way to fix this issue is to

round the price sense first so that this

method doesn't have to do any rounding

so at the front here let's just type

math.round Open Bracket and close

bracket so this is just a tricky issue

that I discovered with the help of AI

recently we just need to add a little

bit of code here to fix it

so now let's save this

file and go back to payment

summary so now that we generated all

this HTML and inserted our numbers into

it let's put this HTML on the page so

inside checkout.

HTML let's give this payment summary

another class

js- payment Das summary and then we'll

select this using the Dom so now let's

save this

file inside payment summary at the

bottom after we create the HTML we're

going to document. query selector

brackets and a string and we'll select

js- payment D summary to get that

element and we'll change the HTML inside

that element using do inner Capital H

HTML and we'll make it equal to the

payment summary

HTML that we just created so now let's

save and check our

project and now these numbers on the

right should match what we have in the

cart and the delivery options that we

selected so that's how we generate the

HTML for this section

here now let's save our changes into git

we'll open

git and it will tell us in checkout.

HTML we removed the HTML we created

manually in delivery options. JS we

created this shared function for finding

the full delivery option and the same

thing in products. JS for finding the

full

product inside checkout. JS we're now

running all the code inside payment

summary in order summary we're just

using those shared functions that we

created and then in payment summary we

calculated the numbers and generated all

the

HTML and finally in money. JS we fixed a

small bug related to rounding let's type

a message to describe our changes save

data and generate

HTML for payment

summary and commit

the last step is to make it interactive

in MVC this is called the

controller let's go to our

project and one thing we can make

interactive in this section is the place

order button however we haven't figured

out how orders work yet so we'll work on

this in the next lesson another thing we

can make interactive however is when we

change the cart on the left these prices

should also update so let's make this

interactive first when we delete a

product the prices here should update so

let's actually practice using MVC to

create this

functionality according to MVC when we

click delete we should update the data

and then regenerate all of this

HTML so let's get started and go to the

code for the delete link so this is in

the order summary section so in our code

let's open the orders summary. JS

file and we'll scroll down and find the

event listener for the delete link which

is right

here when we click delete first we're

going to update the

data so we already update the data using

this function remove from cart

and now the next step according to MBC

is to just regenerate all the

HTML so to regenerate the HTML for the

payment summary we created this function

at the top render payment

summary so this will recalculate all the

numbers and then regenerate the

HTML so let's import this

function in order summary. JS we'll

scroll to the top

and down here we can import curly

brackets the render payment summary

function from a string and we'll locate

the payment summary file so it's in the

same folder so we're going to start with

a slash which is the current folder the

payment summary. JS file and now let's

use this function in the event listener

so let's scroll

down when we click delete we're going to

update the data and then regenerate all

the HTML using render payment summary

brackets now let's save and go to our

project focus on the numbers on the

right here and now let's click

delete and you'll notice that all of

these numbers updated to match our new

so that's another example of using MVC

when we click delete instead of using

the Dom to change these numbers one by

one we just update the data and then

regenerate all of the

HTML MVC makes sure that the HTML always

matches the data or that the view always

matches the

model let's do one last example of NBC

for this lesson when we change the

delivery options here we also want these

numbers on the right to update so let's

find the code for the delivery options

again this is in the order summary

section so in our code we'll open orders

summary. JS scroll down and then here we

updated the data and then we're just

going to regenerate the HTML for the

payment summary using render payment

summary and and

brackets now let's

save and then look at our project and

let's try changing the delivery option

here and you'll notice the numbers on

the right update automatically to match

the cart and that's it we finished the

checkout page so now let's save our code

into git we'll go into the git

section here and inside order summary we

basically imported the render payment

summary function

and then at the

bottom we used MVC so when we click

delete we update the data or the model

and then we regenerate all the HTML or

regenerate The View down here same thing

when we click a delivery option we

update the data and then regenerate all

the

HTML the last thing we're going to do is

at the top of this file

we're going to remove this practice code

that we use to learn external libraries

so let's open orders summary.

JS and at the top we're going to remove

this

code and

save now let's go back into

get and that looks good finally let's

type a message describing our

changes make

payment

summary

interactive and

commit and that's the end of this lesson

in this lesson we learned about external

libraries which is code that is outside

of our project we learned about the DJs

external Library which helps us work

with dates we also learned how to use

external libraries with JavaScript

modules together as well as the default

export syntax we created the delivery

section of the checkout page we learned

MBC which is a better way to design our

code and we created the payment section

of the checkout

page thanks for watching this course so

far if you want to support this channel

you can check out the premium version of

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can get a certificate of completion and

a Better Learning platform if you're

interested in extra videos from me more

in-depth videos and behind the scenes

content you can check out these links

here you can also support the channel by

liking the video subscribing and sharing

this video with others thanks again and

let's continue with the

course here are some exercises to help

you practice what we learned in this

lesson e

in the rest of this course if you get an

error in your project but your code

looks correct you may have some bad data

saved in local storage to fix this you

can try running local storage. CLE in

your console to remove everything from

local

storage and then refresh the

page if you see an error like this

object object that means that you saved

something directly into local storage

but you have to json.stringify it first

so check your code to make sure that

you're always stringifying before saving

to local storage and then clear your

local storage and refresh the

page in this lesson we're going to learn

how to test our code so when we're

writing code it's important to test our

code to see if it's working correctly

and if you're working at a company in

the future you'll also be expected to

test your code so let's learn how to do

that in this

lesson the easiest way to test our code

is to just open the website and try out

the code for example in our code here

let's open the file utils money.jpg

server so on this website we have a

couple of prices here as well as here

and we created these prices using the

function format

currency so if we just look at the

website we can see that these prices

look correct and this tells us that the

function format currency is working

correctly so that's one way to test that

function we just open the website and

try it out so this is called manual

testing when we manually open the

website and try our code so manual

testing is really useful for quickly

checking to see if everything is

working so now let's talk about the

disadvantages of manual testing one

disadvantage is it's hard to test every

situation for example here we just

happen to have the number

295 and we test with that however what

if we want to test with different

numbers like the number zero or a number

that requires rounding like

2.5 in order to test all these

situations we have to manually set up

our website so that our code runs with

those numbers so here we ran with 2095

as well as zero so we covered those

situations however we did not cover

2.5 so we have to do a bunch of setup in

order to test that situation

so as you can see it takes a lot of time

and effort to test different situations

in our code the second disadvantage of

manual testing is that it's hard to

retest the code for example if we change

some of our code how do we retest format

currency and make sure that it's still

working

correctly well we would have to open the

website and set up all the situations

again and retest all those situations

manually so this takes too much time and

effort to retest the

code to solve these two problems we're

going to learn another way to test our

code called automated

testing automated testing basically

means using code to test code instead of

manually opening the website and

clicking around to try our code we're

going to tell the computer to do these

tests for us and this will save a lot of

time and effort so let's go ahead and

create our first automated test we're

going to go back to our

code and again let's test this format

currency function to create an automated

test we're just going to write some code

to test this function so first let's

create a folder to group all of our test

code together we're going to click this

icon to create a folder and let's just

name this tests and press enter

and we're going to move this folder so

we'll drag it to the top level here

beside the HTML

files so we want the test folder to be

beside the scripts

folder next let's click on the test

folder and we're going to create our

first test file we'll click

this and we're going to test format

currency which is inside the money.jpg

money

test.js so we know that this file

contains tests for money. JS so let's

press

enter and inside this file we're going

to write some code to test format

currency so first let's import format

currency so we can test it at the top

we'll type import curly brackets format

currency

from a string and from here we're going

to locate money. JS so we start out in

money test.js and we need to get out of

the test folder so we'll type do do

slash to get out of this folder and then

we'll go into the scripts folder scripts

slash and then into the utils folder

utils slash and locat

money. Js

so as a reminder format currency takes a

number in cents like 295 cents and then

converts it into Dollars like

$20.95 so first let's test this function

using that number 2095 as an example

we're going to run the function format

currency brackets and give it

295 and now we're going to check if the

result of this function is correct to do

that we can just use an if statement so

we'll type if Open Bracket close

bracket and we said we expect format

currency

295 to give us the string

20959 and curly brackets and and if

these two are equal that means the code

is working correctly so we're going to

console. log the string

passed to say that this test has passed

now if it is not equal to

20.95%

failed and

save and that's it this is our first

automated test it checks if the result

of this function is correct if it is

correct we're going to display past and

if it's not correct we're going to

display

failed now let's run this test code so

remember we can't run JavaScript files

directly we need to load this Javascript

file using an HTML file so let's create

an HTML file to run this test inside the

test folder we're going to create a new

file by clicking up

here and let's name this file

tests.

HTML and press

enter and in here we're going to start

by creating a basic HTML structure so as

a reminder at the top we'll type less

than exclamation

dock type space HTML greater than and

we'll create an HTML

element and then inside we'll create a

head

element as well as a body

element and then inside the body we're

going to create a script tag to run

JavaScript

code and we're going to give the script

tag an attribute called SRC or source

equals double quotes and we're going to

give it this JavaScript file to

run money

test.js and also because this file uses

import we also need to add an attribute

called type equals modules to give this

file access to JavaScript module

features like

import so now let's

save and we're going to run this file in

live server so we're going to click it

and then

rightclick open with live

server and then we're going to check the

console by right

clicking

inspect and open the

console and our code display the text

passed so if we look at our

code and open money

test.js it's telling us that the result

of this function matched what we

expected

and this test

passed so that's how we run an automated

test we just load it like normal

JavaScript so as you can see automated

tests are pretty straightforward we're

just using code to test

code okay so I mentioned earlier that a

disadvantage of manual testing is it's

hard to test every

situation now let's solve this problem

using automated

tests so inside money

test.js if we want to test format

currency in different situations or with

different numbers we can just add some

more tests at the bottom so at the

bottom let's create some new lines and

we'll just add another test using IF

brackets and curly

brackets and inside here let's test

format currency with the number zero so

we'll type format

currency brackets 0 and we expect this

result to be the string 0.0 0 so we'll

check if this triple equals the string

0. if this result matches we're going to

console.log the string

passed and if this result does not match

we're going to type else curly brackets

and

console.log the string

failed so that's how we test format

currency in a different situation with

the number zero so now let's

save and then go back to our test page

which is here and then open the console

right click

inspect the

console and it will tell us that both of

our automated tests

passed so as you can see automated tests

help us test our code in different

situations very easily this is a lot

faster than manually opening our website

and setting it up to test with different

numbers so let's go back to our

code and by the way another name for a

situation that we're testing is called a

test case so here instead of saying

we're testing two different situations

we usually say we're testing two test

cases okay now let's get more practice

and add another test case at the bottom

of this file we're going to create

another if statement if brackets and

curly

brackets and this time let's test format

currency brackets and we'll give it a

number that requires some rounding

so when we calculate the 10% tax on our

website the result could be a decimal

like the number

2000.5 if we use the number

2.5 this will convert into $20 and

0.5 however we can't have

0.5 so we're going to round this up to 1

cent so we're going to have $20 And1

so let's check if this result triple

equals the string

20.1 and if it is equal we're going to

console.log

past and if it is not equal else curly

brackets

console.log

failed and

save and open our test page and open the

con

and you can see that all three of our

test cases passed and that's it we just

created three test cases for format

currency using automated

tests now let's go back to our

code and currently we have three test

cases and you might be wondering how

many test cases should we have generally

we create two types of test cases basic

test cases and edge

cases a basic test case just tests if

the code is working or not so here our

first test case is a basic test case we

use a normal number like

2095 and we see if format currency is

working

correctly the second type of test cases

that we should have are edge cases this

means we test a code with values that

are a little bit bit tricky they're on

the edge of what our code can handle for

example in our test here the last two

test cases are edge cases zero is sort

of a special number that's not positive

or negative and

2.5 is a number that requires some

rounding so these numbers are acceptable

we can use them with format currency but

they're a little bit tricky and on the

edge of what our code can handle

so when creating test cases make sure to

create basic test cases as well as edge

cases if there are any edge

cases now we could have added another

basic test case like format currency

1095 however this is very similar to

2095 it's basically testing the same

thing so we don't need another test case

like this generally we should try to

test something different in each test

case for example an edge case that we

have not tested is a number

200.4 so this would check if the code

rounds down correctly to $20

and0 however I'll leave creating this

test case as an

exercise now let's move on and talk

about the second disadvantage of manual

tests which is it's hard to retest the

code automated test also solve this

problem for example let's say that we

Chang the format currency function so

inside UIL money.jpg

we would have to open up the website set

up everything manually and then click

around to see if it's

working however with automated testing

all we need to do is to rerun all of

this test code and it will instantly

retest all of these cases so let's go

back to money. JS and save this

code and then go into our test

page and check our console right click

inspect the

console and you can see that it

instantly reruns all the test cases and

it tells us that the last test case

failed so automated tests make it really

easy to retest our code after we make

any

changes okay now we have another problem

here we can see that the test Cas is

passed passed and failed but it's not

clear which ones passed and which ones

failed we don't really have a name for

these tests so we don't know what

they're doing so that's what we're going

to add next we're going to give each of

these tests a name so let's go back to

our

code and open money

test.js and now we're going to give each

of these test cases a name so above the

first test

case let's just

console.

log a string and we're going to give

this test a name so the name should

describe what this test is doing so in

here let's just use the name converts

cents into

dollars and that's how we give a test

case a name let's do the same thing with

the other two test cases so down here

we're going to console.

log brackets and a string and we give

the second test case a name so this one

tests the number zero so let's use the

name works with zero so again the name

just describes what the test is

doing and let's do the same thing for

the third test case we

console.log a string and here we're

testing if the function rounds up to the

nearest scent so let's use the name

rounds up to the nearest

scent and

save if you're wondering how I came up

with these names a naming convention

that we use is to describe what the code

is doing for example the code works with

zero or the code rounds up to the

nearest scent and then we remove the

code some people also like to use the

word it instead of the

code so now each of these test cases has

a name above it if we open up our test

page and open the

console now we can see exactly which

test case passed and which test case

failed so this failed test case tells us

we have a rounding problem in our code

so now we can go back to our code into

money. JS and investigate the rounding

problem so of course we removed

math.round as an example we're just

going to add it back to fix that failing

test capital m

math.round Open Bracket and close

bracket and

save and then open the console for our

test which is here and now all of our

test cases

passed next another thing we do when

naming our tests is to group related

tests together for example these three

test cases are for the format currency

function so we're going to group these

tests together and give this group a

name by the way a group of related tests

is called a test

Suite so let's go back to our code and

open Money test.js

and at the top let's give this group of

tests or this test Suite A Name by

typing

console.log brackets and a string we're

going to name it test Suite colon format

currency and

save so now let's open the console for

our

tests and now at the top it will show us

test site format currency so this makes

it clear that this group of tests here

are for the format currency

function in the future if we are testing

some other code for example a calculated

tax function we can create another group

of tests or another test Suite like this

and this makes it clear that the second

group of tests is for the calculate tax

function so this is how we name our

tests and group our tests together

together to make it more clear what is

being tested and which tests have passed

or

failed and now we created our first set

of automated tests as you can see

automated tests are basically using code

to test code and they make it really

easy to check if our code is working

correctly so now let's save this into

git we're going to open the git

section and our first change in money

test.js we created the tests for format

currency and then we created an HTML

file to load our test

code so let's create a message

describing these

changes create automated tests for

format

currency and

commit next we're going to learn how to

use a testing framework to write

automated tests so what is a testing

framework in the previous lesson we

learned about external libraries which

is code that is outside of our project

that someone else wrote and we can load

external libraries into our project and

use

them so a testing framework is an

external library that helps us write

tests

easier let's go back to our code and

we're going to open the money test.js

file and notice that in our tests we

need to do several things first we

create a test suite and we give it a

name and then we create some tests and

for each test we give it a name and then

we compare the values and display the

result in the console so a testing

framework helps us do all of these

things automatically and gives us many

other features so now let's learn our

first testing

framework in this course we're going to

use a popular testing framework called

Jasmine now if you're working at a

company in the future you'll definitely

be using a testing framework but it

might not always be Jasmine and that's

okay because most testing Frameworks are

pretty similar so by learning Jasmine

you'll be able to easily use other

testing Frameworks in the

future to load Jasmine into our project

we're going to go into the video

description and we're going to click

this link to download

Jasmine so once that link opens we're

going to be on this page and we're going

to scroll down and we're going to click

this Jasmine DST standalone. zip file to

download it

now once that's finished downloading

we're going to open our downloads

folder and if you're on Windows we're

going to rightclick the zip file and

click extract

all and click

extract now if you don't have that

extract all option you can also create a

folder with this name and then double

click the zip file and drag everything

into that folder

if you're using a Mac you can just

doubleclick the zip

file so this folder contains the code

for Jasmine and we're going to drag this

folder into our project so let's open

the code for our

project and then we're just going to

drag this folder down

here and click copy

folder so just make sure that this fold

folder is beside the scripts and images

folder next we're going to rename this

folder so we'll right click

rename and let's rename it to

test- Jasmine to make it clear this

folder contains test created with

Jasmine so now let's press

enter and now we have Jasmine inside our

project so inside the lip folder we have

some JavaScript files here and this is

the code for the Jasmine testing

framework so this is another way to load

an external Library into our project we

can just download all the code and put

it into our project and this is useful

if an external library has lots of

different files like

this before we continue let's save the

changes into git so if we make any

changes later it will be easier to see

them we'll open the git section

and then we just added all the code for

Jasmine so at the top let's type the

message add Jasmin testing

framework and

commit now that we loaded Jasmine into

our project let's learn how to use it so

Jasmine has a documentation page that

shows you how to use the testing

framework however to save time I'm just

going to show you the features that we

need and you can read the documentation

later if you want so first let's learn

how to run tests using

Jasmine I'm going to close this for now

and then in our code we're going to open

the test- Jasmin folder and at the

bottom we're going to open this spec

runner. HTML

file so this file loads all of the

tests so this does the same thing as our

test.html file from before and by the

way in Jasmine spec is another name for

test so spec Runner just means test

Runner this file runs all the

tests so let's actually rename this file

to test.html so we can match what we had

before and compare the two so here we're

going to right click and

rename

tests. HTML and press

enter and now let's open this file and

take a look at the code that's

inside so here at the top this is the

code for the Jasmine testing framework

so we're just loading the framework up

here below that here we have the code

that we want to test so this code is

sort of like the money JS file that we

were testing

earlier and then at the bottom these

files contain the tests so these files

are sort of like the money test.js file

that we had earlier and you'll notice

that these are in a spec folder so as a

reminder in Jasmine spec is another name

for test so this is basically the test

folder this folder contains all of our

tests so now let's run these tests and

to do that we just need to open this

HTML file in live server just like we

did before

so for this file we're going to right

click and open with live

server and I'm just going to make this a

little bigger by pressing control equals

so it's easier to see in the

video so this is what Jasmine tests look

like up here we have five Green Dots

this means we have five tests that we

ran and the green color means that all

of them passed so that here each test

has a Green Dot and you'll notice that

each test also has a name next to it

which tells us what the test does and

don't worry if this is in a different

order for you Jasmine randomizes the

order of the

tests also notice that some of these

tests are grouped together into a test

suite and up here we have the name of

the test Suite so as you can see a

testing framework helps us do all of the

things we were doing before and it also

provides a nice looking website where we

can see the test results so a testing

framework is just an external library

that helps us write tests

easier now that we know what Jasmine and

a testing framework is let's learn how

to write our tests using

Jasmine first we're going to go back to

our

code and we're going to remove the

example code provided by

Jasmine so down here we'll remove these

four script

texts and let's also remove the source

folder so we'll right click

delete as well as the spec folder right

click

delete but make sure we keep this lib

folder because this contains a code for

Jasmine and now inside test Jasmin we're

going to create a new file for our test

so we'll create a new

file and let's say that we're testing

money. JS again so let's name it the

same thing here money

test.js and press

enter and now let's create the same test

we had before by using Jasmine this time

so to make it easier for the video I'm

just going to take this file and drag it

to the top here so we can see these two

side by

side so like before we're going to

create tests for format currency first

we'll need to import this function at

the top so let's just actually select

this and right click

copy and then down here right click and

paste and just make sure that this file

path still works so our money test.js

file has to be inside test- Jasmin and

this folder should be beside the

previous test

folder next we're going to create a test

suite and name the test Suite so in

Jasmine to create a test Suite we're

going to use a function called

describe so this describe function is

provided by Jasmine and it creates a

test

Suite next we're going to give a name to

the test Suite so to name a test Suite

in Jasmine we're going to give describe

a string and this string is the name of

the test Suite so let's name it the same

thing as before test Suite colon format

currency next we're going to add some

tests inside the test Suite to do that

we're going to give describe a second

parameter which is a function brackets

arrow and curly

brackets and inside here we're going to

create a test and give the test a name

to create a test in Jasmine we're going

to use another function called it and

brackets so it is a another function

provided by Jasmine and this creates a

test next let's give a name to our test

so that we know what it's doing to name

a test we're going to give it a string

and this is going to be the test name so

let's name it the same thing we had

before

converts sense into

dollars and now we're going to add some

code into our tests to do that in

Jasmine we're going to give it a second

parameter which is another function

brackets arrow and curly

brackets so this is the code inside the

test and in this test we need to compare

these two values and display the result

in Jasmine instead of creating an if

statement and displaying the result

ourselves Jasmine provides us another

function to do all of this

and that function is called expect and

brackets so expect lets us compare a

value to another value for example let's

give expect the first value that we want

to compare which is format currency

2095 so we'll type format

currency brackets

295 and now to compare this value to

another value expect gives us an

object and this object has many methods

we can use to do

comparisons so one of the methods we can

use in this object is dot 2 equal

brackets and then inside these brackets

we'll put another value that we want to

compare this to so we want to compare

this to the string 2095

and that's it this checks if this value

is equal to this value and then displays

the result on the page so it does

everything that we did before except

with one line of code and you'll also

notice that jasmin's code is designed so

that it reads like English for example

we expect format currency

2095 to equal this string and this makes

a test code easier to read

so we just created our first test suite

and our first test using

Jasmine now let's run this test to do

that we just need to run this Javascript

file inside test.html

so first let's save this

file and then inside test.html we're

going to load this file so in here at

the bottom we're going to create a

script tag

and we'll give it a source attribute SRC

equals double

quotes and we're going to load money

test.js

test.js and remember our test file uses

import so we also need to give it the

attribute type equals module so this

file has access to JavaScript module

features so now let's save

and we'll open this file in our browser

so we should have it open from before if

you don't you can write click and open

with live

server so we'll open the test page and

now you can see that we have our one

test that we created here and it's

passing so it's green you can see here

that we created a test Suite with a name

and we also created a test with this

name so we just created the first test

that we had before except using Jasmine

this time and you can see that Jasmine

also creates a nice website for us to

see the test

results okay now that we learned how to

use Jasmine to create a test let's get

some practice and create the rest of our

tests from before we'll go back to our

code and open money

test.js and here we're going to create

the other two tests that we had here so

at the bottom inside the same test Suite

we're going to create another test using

the function it brackets and we'll give

it a string which is the test name and

let's name it the same as

before works with zero comma brackets

arrow and curly

brackets and now we can put something

inside this test so in the second test

we're going to compare these two values

to compare values we're going to use the

function expect

brackets and the first value is going to

be format

currency brackets

zero and then expect gives us an

object and this object has a method

called dot to equal which lets us

compare this value to another value

so we'll call this method using brackets

and compare to the string the string 0 0

0 and now let's

save and live server will update our web

page automatically so we'll open the

test page and now we have two tests and

they both passed so that's how we create

the second test using Jasmine and again

don't worry if this is in a different

order for you Jasmine randomizes the

order of the

tests finally let's create that third

test that we had before we'll go back to

our code and then in our old money test

file we're going to create this third

test feel free to pause the video if you

want to give it a try

yourself so we'll scroll down and we'll

create another test inside this test

Suite using the function it brackets and

a string and we'll give it the same test

name as before

rounds up to the

nearest set comma brackets arrow and

curly

brackets and we're going to compare

these two values so we use exp brackets

and give it the first value format

currency brackets

2000.5 and to compare it we'll use the

method

do2 equal brackets and compare it to

20.01 and

save and let's go back to our test page

and now we have three tests and all

three of them passed so we recreated the

tests that we had

before now let's try making one of these

tests fail to see what it looks like in

Jasmine we'll open our

code and and let's open the file utils

money.jpg

test so it tells us the test Suite name

and the test name that failed and it

will also tell us the two values that

are not equal to each other and here it

will tell us where this test failed so

it tell us that it failed in money

test.js at line

13 so if we go back to our

code and we open the Jasmine money

test.js line 13 is right here so just

telling us that this line failed the

test

here we can see the full list of tests

and it will tell us that we have three

tests two of them passed and one of them

failed so Jasmine gives us a lot of

details on where a test failed to help

us fix the

issue now let's add back math.round to

make everything pass again we'll open

our code and open UTS money.jpg

math.round Open Bracket and close

bracket and

save and if we check our test page

everything passes

again so this is how we use a testing

framework like Jasmine to create tests

the testing framework gives us a bunch

of functions such as describe it and

expect and then we use these functions

to create our test so so these functions

have a lot of features inside them they

do all of the setup for us and they also

display the test on a nice web page for

us now there's one more thing I want to

mention which is we can use describe

inside describe this helps us organize

our tests

further so now let's save our changes

into git we'll open the git

section and let's close this file at the

top for

now so inside money test.js we created

all the tests that we had before for

format currency by using Jasmine this

time and for spec Runner we rename this

file to test.html and finally we deleted

all the test code that came with Jasmine

so now let's add a message to describe

our

changes

remove default tests and add

money tests and

commit now let's test a different

function using Jasmine and along the way

we're going to learn some more features

of testing

Frameworks let's go back to our

code and we're going to scroll to the

top and open the data/ cart. JS

file so inside this file we have a

function called add to cart so we're

going to create tests for the add to

cart

function first since this function is in

a different file we're going to create a

new test file so we're going to scroll

down and let's close the test folder so

we don't get confused and then inside

test- Jasmine we're going to click in

this folder and then create a new file

and let's name it cart

test.js and press

enter so we name it the original file

name which is cart and then just add

test at the

end and to better organize our test

files we usually try to match the folder

structure of the code so for example in

our code money. JS is inside this UIL

folder so inside our tests we should

also create a utils folder and put this

file inside so we'll create a new folder

by clicking up here and let's name it

utils and press

enter and then move the money test.js

file

inside if it asks you if you want to

update Imports automatically you can

click

yes if you check your code scroll to the

top make sure that your file path starts

with do do slash do do slash because now

we're inside another

folder VSS code sometimes updates the

file paths for us automatically but if

it doesn't we can just add an extra dot

do slash in front

ourselves and we're also going to open

money test.js and save this

file next if we scroll up cart. JS is in

inside a data folder so inside our tests

we're also going to create a data folder

let's click cart

test.js we'll create a new folder and

let's name this the data folder and

press

enter and then move card test.js inside

here now you'll notice that this folder

structure doesn't perfectly match the

folder structure that we have up here

because utils is inside the scripts

folder but usually this data folder

should also be inside the scripts folder

I just made a mistake when structuring

the

project so let's just use this folder

structure in our

tests okay so now let's open cart

test.js and now we're ready to test the

add to cart

function so first let's import add to

cart at the top we'll import

curly brackets add to

cart from a

string and we're going to locate cart.

JS so first we need to get out of the

data folder using do slash and then get

out of the test djine folder do do slash

and we'll go into this data folder data

SL cart.

JS next let's create a test suite for

this function so we'll create some new

lines and to create a test Suite in

Jasmine we'll use the function

describe

brackets and we'll give this test Suite

A Name by giving it a

string so let's use the name test Suite

colon add to

cart and we'll give it a second

parameter which is a function brackets

arrow and curly

brackets and now inside this test Suite

we're going to add some tests so let's

look at the code for add to cart to see

what kind of tests we should

add so we'll open data/ cart.

JS and then inside add to cart you'll

notice that this function uses an if

statement a best practice in testing is

to test each condition of the if

statement

this is known as test coverage test

coverage means how much of the code is

being tested and a best practice is we

try to maximize test

coverage so for this if statement we'll

create a test for the first condition

which is when the product is already in

the cart and we'll create a test for the

else condition when the product is not

in the

cart let's go back to cart

test.js and inside this test Suite we're

going to create a test using the

function it brackets and we'll give it a

string and this will be the test name so

for the video I'm just going to scroll

up and take this cart. JS file and put

it at the top here so we can see our

code and our test side by side so I'm

going to scroll down to the add to card

function and we mentioned that we're

going to test each condition of this if

statement so the first test is going to

be when the product is already in the

cart so that here let's name it ads and

existing product to the cart comma

brackets arrow and curly

brackets and let's add another test for

when the product is not in the cart so

this else condition so down here we'll

create another test using it brackets

and a string and the test name adds a

new product to the cart comma and a

function brackets arrow and curly

brackets so these are the two tests that

we need for the two conditions of this

if

statement let's actually start with

adding a new product to the cart since

it's a little easier to

test now unlike the format currency

function add to cart doesn't return a

value so we can't really compare it to

another value using

expect instead we're going to call add

to cart to modify the cart and then

check if this cart looks correct to do

that inside here let's call the function

add to cart

brackets and this function takes one

string which is the product

ID so inside here let's give it a string

and to find a product ID that we can

test with we're going to go to the left

and scroll up and we're going to open

the data/ products. JS

file and inside here we have a list of

products so let's just take the first

product ID and use it in our test we're

going to select this ID and right click

copy and then inside cart

test.js in this string we're going to

rightclick and

paste so this will add this product ID

to the cart and now to check if this

code is working correctly we're going to

check what the cart look looks like so

first we need to import the cart we're

going to scroll up and since we're

already importing from cart. JS to UT

the cart we can type a comma

cart and then at the bottom here we're

going to create a new

line and first let's check if the card.

length is correct so if we assume that

we start with an empty cart when we add

a product the cart. length should should

be one so we can compare these two

values cart. length and one so to

compare values we're going to use the

function expect brackets and we'll

compare the

cart.

length and then here we'll use the

method2 equal brackets

1 so now let's save this

file and we're going to run these tests

to run them we're just going to load

this file inside test.html so we'll open

this and then at the bottom we'll create

a script

tag give it a source attribute double

quotes and we're going to load this file

so this file is inside the data folder

so we need to type data SL to go into

the folder and then load cart test.js

and this file also uses import so we're

going to give it the attribute type

equals module to enable JavaScript

module

features and one thing that I forgot to

do is we moved money test into the util

folder so we need to update the source

attribute to add the utils folder and

then slash to go into the folder and

then locate money

test.js so now let's save this HTML file

and open this test page in our

browser and now we should have two

additional tests and the test that we

just created should fail if it doesn't

fail for you you can go into your

console and run local storage. CLE and

then refresh the page and it should

fail so this tells us that the failure

happened in the test suite at Dart in

the test adds a new product to the cart

which is the one we just

created so it's telling us that the

cart. length is not equal to one it's

equal to a different number so why is

this happening let's go back to our

test open cart

test.js and in here remember that we

assumed the cart starts as empty and if

we add a product the card dot length

would be one however the cart doesn't

actually start as

empty in cart. JS at the top here we're

loading the cart from local storage if

there's nothing in local storage we use

this default cart so our starting cart

depends on what's inside local storage

and this is a big problem when testing

because local storage can change if

there's an empty card saved in local

storage our test will pass but if

there's not an empty cart in local

storage then this test will fail this is

known as a flaky test a test that

sometimes passes and sometimes fails

even if we don't change the

code now to solve this problem we're

going to use a feature of Jasmine called

mocks a mock lets us replace a method

with a fake version and then we can make

the fake version do anything we want for

example

when we load the cart from local storage

we're using local storage. getet item so

we can use a mock to create a fake

version of get item and then we can make

this fake version do anything we want

like return an empty

array so let's go ahead and create our

first

mock we'll go back to cart

test.js and at the top of this test

we're going to create a mock using

another function of Jasmine called spy

on and

brackets and we'll give spy on two

parameters the first parameter is the

object that we want to mock in our case

it's local storage so we'll type local

storage comma and then we'll give it a

string and this string will be the

method that we want to Mark in our case

we want to Mark the get item method so

here we'll type get item and make sure I

is uppercase so that we exactly match

the method

name so now this will replace local

storage. getet item with a fake version

and we can make this fake version do

anything we want to do that spy on gives

us an object and this object has a

property we can

use so at the end we'll type Dot

and the property called

an and this result is also an object and

this object has a method called dot call

fake brackets so don't worry about all

the Dots here Jasmine just organizes its

code so that it reads like English so

we're spying on local storage. getet

item and call fake so next we're going

to give call fake a function brackets

arrow and curly

brackets and this function is what we

want get item to do so we're essentially

overwriting the original get item with

whatever is inside this

function so earlier we said we wanted

get item to return the empty array for

this test so inside this fake function

let's make get item return the empty

array

now remember that local storage only

supports strings so we need to return

this as a string to do that we're going

to use the code Json all uppercase do

stringify Open Bracket and close bracket

so this will convert whatever is in the

brackets to a Json string and that's

what we need for local

storage so now let's test out this mock

to see if it works

below this we're going to

console.log

brackets and run local

storage doget capital I item brackets

the string

cart let's save this file and then open

the test page in our

browser and we're going to open the

console so

rightclick inspect

and the

console and you'll see that Here Local

storage. getet item is no longer loading

from the actual local storage it's

giving us an empty array every

time so now we have mocked the get item

method however you'll also notice that

our test is still failing so how come it

still

fails to understand what's happening

let's take a closer look at our code

we'll go back to our

code and inside our tests here we're

mocking local storage. getet item but

notice that above this if we scroll up

we import the cart at the top so the

order of this code matters first we load

the cart from local storage and after

we're mocking local storage. getet item

so the card is already loaded at this

point and this code doesn't have the

effect that we

want so one way to solve this problem is

after we mock local storage here we

should reload the cart so inside cart.

JS just going to give it a little more

space to reload this cart after we mock

we just need to rerun all of this code

so let's create a function so we can

rerun this code at the bottom here we'll

create a

function and we'll call it load from

Storage brackets and curly

brackets and we're just going to move

all of this code inside the function so

let's select all the code up to cart

equals we'll

rightclick

cut and then in the function we'll

rightclick and paste

and at the top let's create the cart

variable again let cart and

semicolon and lastly when we load this

file we need to run this function so

that we run this code at least

once so down here we'll just run this

function load from storage and

brackets so let's

save so we're basically running the

exact same code as before except this

code is now inside a

function and now in our

test after we mock local storage. getet

item we're going to reload the cart

using this function so first let's

export it so we can use it in our test

we'll type

export and save this file and Insider

test let's scroll up to the top we're

already importing from cart. Js so we'll

type a comma and we'll import load from

storage and then we'll scroll down back

to our test and here after we mock local

storage. getet item we're going to load

from Storage brackets and

save so this time we mock local storage.

getet item first to return an empty

array and then when we reload the cart

this is going to be an empty array and

the cart will be empty and now in our

test when we add a product to an empty

cart the cart length will be equal to

one so this test will pass so we can

actually remove the console.log here and

save and check our test

page and now this test should be

passing next let's go back to our code

Cod and if we look at the add to cart

function in cart.

JS so in here at the bottom of this

function you'll notice that we're saving

the cart to local storage so this is

going to call local storage. set

item however we don't actually want to

save to local storage because this is

just test code we don't want our test

code to be modifying local storage or

affecting our real code

to prevent this we're also going to mock

local storage. set

item so down here we're going to create

some new lines at the top of the test

and we're going to mock local storage.

set item using the function spy on

brackets and we'll give it local

storage comma a string and the method we

want to mock which is set

item and

save and remember the order of the code

matters so we want to mock local

storage. set item first and then we call

add to cart so now set item will be

replaced with a fake version and this

will no longer save to local

storage next spyon has another useful

feature which is it records every time a

method is used for example what if we

want to make sure that add to cart saves

the cart to local storage at the end in

our tests set item is mocked so we can't

really check what's inside the local

storage instead we can just check if add

to cart calls set item at some

point to check if set item was called at

the bottom we can use the function

expect

brackets and we're going to give this

the method that we loed which is local

storage. set

item and remember that expect gives us

an object and this object has many

useful methods to check stuff like dot

to

equal so another method we get from

expect is dot 2 have been called times

brackets

so make sure that you write this method

in cam case two is lowercase and every

word after starts with a

capital so this method checks how many

times local storage. set item was called

in the code above so we expect it to be

called once inside add to cart so we're

going to give it the number

one so keep in mind that this only works

if this method has been mocked with spy

on so now let's

save and open our test

page and you can see that all of our

tests passed and local storage. set item

was called

once so after we mock a method we can

check how many times this method was

called and we can even check what values

this method received but I'll leave that

as an

exercise another thing you'll notice

here is that each test can have multiple

expectations

and the test will only pass if all of

its expectations

pass now let's add a few more

expectations to this test for practice

so one thing we can check is we can

check the first product in the cart and

make sure that its product ID matches

this string here so below this let's use

another expect brackets and we're going

to check the first product in the cart

using cart square bracket

0 so this is going to be an object and

this object is going to have a property

called product ID so that here we'll get

the dot product

ID and we're going to check if this

product ID is equal to this string so to

do that we'll use the dot 2 equal method

brackets and we'll give it this string

here so let's just select this and

rightclick

copy and here right click and

paste another thing that we can check is

the quantity when we add a new product

to the cart the quantity should start

out as one so down here we're going to

add another

expect

brackets and we're going to check the

first product

cart square bracket

0.

quantity. 2 equal brackets one and

save now let's open our test

page and you can see that all of those

expectations

passed now let's move on and create the

test for adding an existing product to

the cart so we'll go back to our code

and scroll up to the first test

here so first we need to set up the cart

so that it already contains the product

that we want to add to do that we're

going to Mark local storage. getet item

again so down here we can just reuse

this code so we're going to select this

code and right

click

copy and then in the first test here

rightclick and

paste and this time do set up the test

we're going to put a product into the

cart at the beginning and then we're

going to add the same product to the

cart so inside this cart array let's add

an

object and each product has a property

called product ID so we're going to add

this property product ID colon

and let's just give the same product ID

that we used down here so we'll select

this and then right click

copy and then up here we're going to

right click and

paste

comma and each product also has a

quantity so we'll give it a quantity

colon and let's just give it one comma

and also a delivery option so delivery

option ID colon and let's just give it

the string

one and

save so now when we do local storage.

getet item it will give back this array

as the starting cart and then we need to

make sure that we reload the cart from

Storage next let's scroll down and let's

copy the rest of the tests because it's

going to be very similar so we're going

to select this code and

rightclick

copy and then up here create some new

lines and right click and

paste and also one thing I forgot to

copy over is to mock local storage. set

item so at the

top let's

also spy on brackets

local

storage comma a string set

item so a mock only lasts for one test

once that test is finished the method is

no longer mocked so that's why in this

test we also have to mock local storage.

set

item and now in this test we're just

going to modify these expectations so

that they make sense for this test

if we add an existing product to the

cart the cart. length will still equal

one because these product IDs match and

we're just increasing the

quantity we're still going to call local

storage. set item once so this is

correct

still the first item in the cart is

going to have this product ID and the

only thing we're going to change is that

the quantity is now going to increase by

one so it's going to go from one to two

this

time so everything is the same except if

we add an existing product we're just

increasing the quantity now let's

save and check the test

page and now the existing product test

is

passing and that's it we created tests

for the add to cart

function so now let's do some cleanup

and we're actually going to remove

everything from local storage since we

were modifying it earlier in the test

and we might have messed it up so on

this page we're going to

rightclick

inspect and open the console and to

remove everything from local storage

we're going to type the code local

capital S

storage. clear and brackets and press

enter and then we'll refresh the

page now finally let's go into get and

save our changes so we'll open our code

and we can close this one for

now and we'll open the get

Section so in cart. JS at the top we

basically put all the code that loads

the cart into a function so we can use

it in our

tests and then here we moved money

test.js into a utils folder in test.html

we're loading the new cart test.js file

and then inside cart test.js we added

some tests for the add to cart function

so now let's create a message describing

these

changes

create

automated tests for add to cart and

commit

the last thing we're going to learn in

this lesson is how to create more

complicated

tests so far we've only been testing a

single function for example we tested

the add to card function as well as the

format currency function so these are

called Unit tests because we're only

testing one unit or one piece of the

code now what if we want to test t a

whole page or part of a page and this

requires a more complicated test called

an integration

test an integration test tests many

units of code or pieces of code working

together for example in our code we're

going to go to scripts checkout thee

orders summary. JS

file and we're going to test this render

order summary function so this function

creates a whole section on the checkout

page and it uses many different

functions and libraries to create the

page so testing this function will be

considered an integration test because

it uses many different pieces of code or

units of code together so let's start by

creating a test file for this function

so this is in the orders summary. JS

file inside our test here let's match

the file structure that we have here

here so we're going to click test-

Jasmin and first we're going to create a

checkout folder so we'll click here to

create a

folder and we're going to name it

checkout and press

enter and then inside the checkout

folder we're going to create a new file

so we'll click this to create a new

file and we'll name it the same as above

order summary and ADD test

.js and press

enter so by matching the file structure

it's clear that this test file is going

to test ORD summary.

JS and again for the video I'm just

going to drag this file to the top here

so we can see this and the test side by

side and now we're going to test this

render order summary function so first

we're going to import this function into

to our test file at the top we'll import

curly brackets the render order summary

function from a string and we're going

to locate this file so first we need to

get out of the checkout folder and out

of the test Jasmine folder so we'll use

two do do slash do do slash and then

we're going to go into the scripts

folder and into the checkout folder

Scripts slash checkout slash and we'll

load order

summary.jpg

[Music]

order summary

a comma and a function brackets arrow

and curler

brackets and now what test cases should

we create render order summary creates a

part of the page so when we're testing a

page the two things we need to test is

how the page looks and how the page

behaves let's start by testing how the

page looks inside our test Suite we're

going to create a test using it brackets

and we'll name this test with a

string and this will just be a basic

test case so we'll describe what this

function does which is

displays the

cart comma and we'll give it a function

brackets arrow and curly brackets and

now we're ready to create the

test so render order summary usually

displays the cart on the page however in

our tests where does this cart get

displayed so if we look at the code in

this

function and we scroll down here we

generate the HTML for the

cart and then after we generate the

HTML we put the HTML inside an element

with the class js- order-

summary however we don't have this

element in our tests so to fix this

we're just going to create an element

with the class js- order-

summary to do this we're going to scroll

down and we're going to open the

test.html

file and then at the bottom we're going

to go to the body and then inside here

we're going to create a div so less than

div and greater

than so remember how we said we need to

create create an element with the class

js- order- summary we're going to create

that element and put it inside this div

so this div is going to act like a

container the reason we use a container

is that when we create elements in our

test we don't want to be modifying the

entire body because the body might

contain our test results from jasine so

we put everything inside a

container so now let's give this div a

class so we can use it in our JavaScript

we're going to give it a class equals

double quotes and we're going to call

this the js- test-

container to make it clear this is a

container for all of our test

code and

save and now let's get this container

into our tests we can do that using

document. query

selector brackets and a string and we'll

select the class using using a js- test-

container and then inside this container

we're going to create an element with

the class js- order- summary so to put

something inside this element we're

going to use the property do inner

Capital

HTML equals a template

string and inside this template

let's create a div element less than div

greater than less than SL div greater

than and as we mentioned we'll give this

element a class equals double quotes of

js- order-

summary so this basically takes this

HTML and puts it inside our test

container so it will put it inside here

and now we have the element that we need

for render order summary so when we call

this function it's going to create the

cart and display it in this element

here next if we look at the code for

render order summary and we scroll to

the

top you'll notice that it takes the cart

and then displays it on the page but

remember that by default we load this

cart from local storage and this can

cause problems in our test depending on

what is inside local storage so to fix

this we're going to mock local storage.

getet item again to control exactly

what's inside this cart so let's

actually open the cart test that we had

before and we're just going to copy

paste this mock that we created so we're

going to start from here this function

and we're going to select the code up to

spy on get item and then

rightclick copy

and then down here we're going to

rightclick and

paste and one other thing we need to do

here is we don't have access to load

from Storage right now so we need to

import it at the

top let's also copy the import that we

had here so we're going to select this

and then right click

copy and then down here we're going to

rightclick and paste the

import and we just need to make sure

that this file path locates cart. JS so

do/ do slash it's going to go outside

checkout and outside test- Jasmin and

then it will go inside the data folder

and then locate card. JS so this file

path is correct and currently we're not

using these two values so we can just

remove

them and now let's set up this cart for

this test so we could just use this cart

here however to make our test a little

more detailed let's open the cart. JS

file and at the top here we're going to

use this default card instead because it

has two products with different

quantities so we can test more things so

we're just going to select this card

here and then right click

copy and then down here open order

summary

test and we're going to select this card

and remove

it and inside these brackets we're going

to right click and paste that default

cart and now that the HTML and the cart

is set up for this function at the

bottom we can call the function render

order summary and

brackets and Save

so now let's run this test file we're

going to open test.html

and then beneath these tests we're going

to add another script Tech less than

script Source equals and we'll load the

checkout slash order summary test.js

file and we need to give it the

attribute type Ty

equals module because we used

Imports and let's save so we run this

test so we'll open our test

page and you can see that the cart was

rendered onto this test page and we

still have our Jasmine results at the

bottom here so you notice that when we

render this it didn't load any CSS or

images and this is okay because we can't

really use code to check if the page

visually looks correct however we can

use this to check the contents of the

page like if the products and the

quantities are

correct so first our cart has two

products in it so we can check if there

were two products that were rendered on

the page let's go back to our

tests and let's take a look at the

orderers summary. JS file

and when we render the order summary we

scroll down for each product in the cart

we create an element with the class

cart--

container since we have two products in

the cart let's check that we created two

of these elements on the page so we're

going to open the order summary test.js

file and then in the first test at the

bottom of this test we're going to add

some lines and we're going to check if

we have two of these elements to do that

we can use the Dom using

document. query selector all brackets

and a string and we could select the

class card- item D container however

this class is used for CSS so remember

if we're going to use a class in

JavaScript we start with js-

let's add a new class to this element

that we can use for the test we'll add

js- cart D item D

container so now we're going to select

all the elements with this class

using js- card- item D

container and let's save the ORD

summary. JS

file and then down here we're going to

check if we have two of these elements

on the page so again to check something

in our tests we're going to use the

function expect Open Bracket and let's

create a new line to make it a little

cleaner and at the end we'll give a Clos

bracket like

this and this code gives us an array of

elements so here we're going to check if

the dot length of this is equal to to

two so expect gives us an object which

has a method called dot 2 equal brackets

and two so this checks if we have two of

these elements on the page so let's

save and then check the test

page and scroll to the bottom and you'll

see that this test

passed so that's how we check if we

render the page correctly

next let's do another check of what we

rendered on the page so another thing we

can test is If the product quantities

are correct so first we need to get this

quantity element into our tests so we'll

go back to our

code and then inside the HTML of the

order summary we're going to scroll

down until we see a div with the class

product- quantity and we're displaying

the Quant

here so now we're going to take this

element put it into our test and check

that the quantity here is

correct so to do that let's give another

class to this element so we can select

it using JavaScript so here we'll add

another class

js-

product-

quantity and we want to check the

quantity for each product so we need to

identify which product this is for we

can do that by adding a dash to this

class and then inserting using dollar

and curly brackets the products ID which

is the matching product matching

product. ID and

save and now let's get this element into

our test so down here we're going to

document. query

selector

brackets and we'll give it a template

string because we're going to insert a

product ID so we're going to select this

class using a js- product- quantity Dash

and then insert the product ID so in our

cart we have two products and let's

start with the first product ID now to

make this easier let's put this string

inside a variable so we can reuse it

below so above the this let's create a

variable with const call it product

id1 equals and we're going to select

this ID and then right click

cut and then up here rightclick and

paste and then we're just going to use

this variable down here product

id1 and then when we're getting this

element into our our code we're also

going to insert the product ID which is

product

id1 but now we're going to check if the

text inside is correct so for the first

product we have a quantity of two so the

text inside this element should say

Quantity colon

2 so to check this at the bottom of our

test as usual we're going to use the

function

expect Open Bracket and a new line and

then here we can remove the semicolon

and close

bracket and we're going to get the text

inside this element now we're not going

to usein HTML because this element

contains a bunch of HTML inside but we

only want the text to get just the text

we're going to use the property do inner

text so we expect the text inside this

element to contain quantity colon

2 however this element also has some

other text like update and

delete so we just want to check if

quantity 2 is somewhere inside this

element so how do we check that to do

that we're going to use a different

method of expect called dot to

contain and

brackets and we're going to give it the

string that we want to check for which

is capital Q quantity colon

2 so the two contain method checks if

this value contains this string so they

don't have to be an exact match like

with two

equal as long as quantity colon 2 is

somewhere in this element then this

expectation will pass and this is

exactly what we need when this El has

some extra text that we don't really

need to

check so now let's click our test file

and

save and open the test

page and scroll to the bottom and you'll

notice that the test passed so for the

first product we're displaying the

quantity of two

correctly let's also check the quantity

of the second product we'll go back to

our

tests and and just like before let's

create a variable to store this ID so

we'll create a variable with const

product

id2 equals and we'll select this

ID and right click

copy and then here right click and

paste and then we'll remove

this and use the variable product

id2 and then at the bottom we're going

to get the quantity element for Product

2 so let's just copy this code because

it's very similar we'll select it right

click copy and then down

here right click and

paste so this time we're going to get

the quantity element for product ID

2 and in our cart product two has a

quantity of one so down here we're going

to check if the text contains quantity

colon 1 and

save and let's open our test

page and scroll to the

bottom and this test passed so we're

displaying the quantity of both products

correctly on the

page the second thing we can test in an

integration test is how the page behaves

for for example on this page we can

click the delete link to remove a

product from the page so let's create a

new test to make sure that the delete

link behaves

correctly we'll open our test

code and at the bottom we're going to

create a new test using the function it

and

brackets we'll give it a name and let's

describe what the behavior should be

which is removes a

product comma and a function brackets

arrow and curler

brackets now let's do the same setup as

the first test so we start with two

products in the cart so we can select

from load from storage and we'll select

all of this code up here and then

rightclick

copy and at the bottom

we're going to right click and

paste so this will set up the HTML

element that we need for the order

summary as well as the

cart and after this let's render the

order summary using the function render

order summary and

brackets so once we've displayed this on

the page we're going to get the delete

link and click it so first let's get the

delete link into our code so we'll go to

the orders summary. JS file and inside

the HTML we're going to scroll down a

bit till we see the delete quantity link

and let's test the delete link for the

first product in the

cart so first we need to add a class to

this element so we know which product

this is for so here we're going to add a

class JF s- delete

dink Dash and insert the product ID

which is the matching

product

doid and I'll add a new line to make the

code a little bit cleaner and now we can

save and then down here we're going to

get the delete link for the first

product ID so at the bottom we use

document do query

selector

brackets and we'll give it a template

string because we're going to insert the

product ID and we'll select this class

using js- delete

dlink D and then insert dollar curly

brackets product

id1 and now we need to click this delete

link to remove the first product from

the page and from the cart to click an

element using Code we can just get it

using the Dom and then use the method

dot click and

brackets so this will click delete on

the first product and remove it so let's

save and take a look at our test

page and unfortunately this test failed

so let's take a look at the details of

the failure to figure out how to fix it

so it's telling us that we cannot set

properties of null this means that a

value in our code is null and we're

trying to give it a

property and here it will tell us which

line we got this error from so this

error happened in our test file and the

line that created this error was in Ord

summary. js on line

132 or whatever line that you see here

on your page

so inside our code we're going to open

orders summary.

JS and I'm going to scroll down to line

132 and you can scroll down to the line

that you got on your

page so this line of code is actually

part of the code that we run when we

click delete so remember that when we

click delete we also update the payment

summary on the right side of the page

and that's what this line does now the

reason this is not working is if we open

the payment summary JS file and we look

at what this does at the bottom after we

generate the HTML we try to put the HTML

in an element with a class js- payment D

summary and this element does not exist

in our tests so one way to fix this is

to add this element to our

test so let's open our test again

we'll open the order summary

test.js and then we'll scroll

up and then here when we create the

order summary element we're also going

to create the payment summary

element so we'll create a less than div

greater than less than SL div greater

than and here we'll give it a class

equals double quotes and we'll give the

class that the payment summary needs

which is

js- payment D

summary and

save so now that the payment summary

element is set up we can open our test

page and our test should no longer have

a failure so you also notice that the

payment summary got rendered or

displayed on the

page okay so in our tests we only

clicked the delete link for the first

product but we didn't actually check if

the page looks

correct and that's what it shows here

with this yellow dot this test has no

expectations

yet so let's go back to our test and add

some expectations at the bottom so we'll

scroll down and down

here after we click delete for the first

product we expect that there's only one

element left on the page for the

cart so in our first test we actually

had a check for this so we can scroll up

and here we check if we have two cart

item containers on the page so let's

just reuse this check because it's very

similar we'll select it right click

copy and then down

here we're going to right click and

paste and this time we only expect one

cart item container to be left on the

page so so we'll change this to one so

we'll

save open the test page scroll down and

now this test

passed let's also do a more detailed

check so we're going to check that the

first product is no longer on the page

we'll go back to our

tests and then down here we're going to

get the card item container for the

first product we use

document. query selector

brackets and to get the element for the

first product we're going to open orders

summary. JS and then scroll up in the

HTML until we find the cart item

container

element and we're going to look for this

class right here which tells us which

product this element is for so in here

we'll give it a template string because

we'll in insert the product ID and we'll

look for this class using a

js-- item Das container Dash and insert

the first product so product

id1 and because we removed this product

from the page we expect this result to

be null so we'll use the function expect

open bracket and a new line and then

down here a close bracket and we'll use

the method

do2 equal brackets and we expect this to

be null and

save let's also check that the second

product is still on the page because we

didn't delete

it so let's just make a copy of this

check we'll select it right click copy

and then

here right click and

paste and we'll get the element for

product ID 2 this time and we want to

make sure that this exists so that it is

not equal to null in Jasmine to check if

something is not equal

to expect gives us another property we

can use called dot

not so if we use theot property it will

check the opposite of whatever is next

so this will check if this value is not

equal to null so remember the code for

Jasmine is designed to read like

English let's save and check the test

page and scroll

down and this test passed so we're

displaying the correct products on the

page after

deleting now there's one more thing that

we need to check here which is after

deleting is the cart array itself

updated so we'll go back to our code and

add that

check so first we need to import the

cart so we can use it in this test we're

going to scroll up to the

top and we're already importing from

cart. JS so we'll add a comma and import

the

cart and then at the

bottom we're going to check if the card

is correct

so the cart started out with two

products inside after removing the first

product the card should have a length of

one and the remaining product should

have product id2 so let's add both of

these checks at the bottom so we'll

scroll back

down and we'll use expect

brackets and we'll check if cart. length

do 2 equal brackets

1 and we'll also expect brackets and

we'll check the first product in the

cart which is cart square bracket 0 and

we'll check its product ID do2

equal and it should equal product ID 2

so product id2

and

save so let's open our test

page and scroll to the bottom and this

test still passed so once we click

delete the card array is also

correct so that's how we create an

integration test it tests many units of

code or pieces of code working together

and it lets us test how our page looks

and how our page behaves

now there's one thing that I forgot to

do when we created these tests if we

look at our

code and I'm going to open orders

summary.

JS when we click delete at the bottom

here it uses a function called remove

from

cart and if I look at the code for this

function which is right here remove from

cart this function actually saves the

cart to local storage and and calls

local storage. set

item however it's recommended not to

modify local storage in our test so

inside the order summary test file we

should also mock local storage. set item

in this test so we'll scroll to the

top and at the start of the test let's

mock set item using spy on

brackets local

storage comma the string set

item and

save and we'll open the test page and

make sure that the test still passes and

we might have messed up our local

storage because of that mistake so let's

reset local storage again we'll right

click on this page

inspect open the

console and we'll type the code local

storage. CLE brackets and press

enter and refresh the page just to be

safe now another thing that we might

want to add is that when we render the

order summary on the page it's taking up

a lot of space and it pushes the test

results to the bottom so what we can do

is after our test we can actually remove

all of this

HTML so let's go back to our code

in the order summary test file at the

end of the first test we'll create some

new lines and remove the HTML that we

created to do that we can scroll up to

this code so to remove the HTML we can

just set this element inner HTML to the

empty string so we'll select this code

right click

copy and then down here right click and

and

paste so in our test all the HTML we

created was placed inside this test

container and we're just going to remove

all that

HTML by setting the inner HTML to the

empty string and we'll do the same thing

for the second test so we'll select this

code rightclick

copy and then down here at the

bottom we'll right click and

paste so this is just some cleanup we

can do at the end of each test let's

save and look at our test

page and now all the HTML that we

generated is gone and we can see the

test results more

clearly lastly we're going to learn a

shortcut we can use in Jasmine called

hooks a hook lets us run some code for

each test for example

if we go back to our code notice that

before each of our tests we do a bunch

of setup here so we can actually share

all of this code between our two tests

using a hook so to create a hook we're

going to scroll up to outside of both of

these

tests and at the top of the test Suite

we're going to use another function

provided by Jasmine called before

capital E

each brackets and we'll give this a

function brackets arrow and curler

brackets so this is called a before each

hook and it will run this function

before each of our

tests so inside this function we can put

our setup code so that we run the setup

code before each of our

tests let's actually take the setup code

for the second test because it's a

little more

detailed so down here we're going to

select the code starting from render

order summary all the way up to mocking

local storage. set item and we'll

rightclick and cut this

code and remove these new

lines and then at the top inside before

each we're going to rightclick and paste

so now before each of our tests it's

going to run this function and it's

going to run all of our setup code so

this is a great way to share code

between our tests and remove

duplication so now that we're running

this inside before each if we scroll

down to the first test we don't have to

run this code again so we can actually

remove

it and we'll remove this Mock and we'll

remove the render order summary as

W and all we're left with are the

expectations for our

test now before we save we need to fix

one thing with this code here so right

now these two variables are inside this

function and because of scope these will

be contained inside this function and we

can't use it down here in our

tests so to fix this we can just move

these variables outside of this function

up here so we're going to select these

lines and then right click

cut and up

here we're going to right click and

paste so now any code inside this outer

function can use these two variables

including our

tests so now let's

save and check the test

page and everything is still still

passing so that's how we use a hook to

run some code before each test now

before each is not the only hook that we

can use Jasmine provides several hooks

that we can use in our

tests another common Hook is after each

which lets us run a function after each

test so this is really useful for

cleanup code like we have down here when

we remove the

HTML all leave using after each as an

exercise now let's go into git and save

our changes and I can close these three

files at the top for

now so we'll open the git

section and then inside orders summary.

JS we added some classes that we're

going to use in our

tests inside test.html we are loading

our order summary test file and we also

created a test container where we're

going to put our HTML that we

generate and then for the order summary

test file this contains the test that we

created for the order

summary now let's create a message

describing our

changes create automated tests for order

summary and commit

now that we've created all these tests

for our project when we make some

changes to our code we can just open the

testing page and it will rerun all of

our

tests so here's the process that we do

when we write code first we make changes

to our code and then we rerun the tests

to make sure that everything still works

and finally we save our changes into

git now before we end the lesson we're

going to do one more cleanup we'll go

back to our

code and we'll open our

files and here we usually organize all

of our tests into a folder called tests

however in this lesson we named this

folder test- Jasmin because we wanted to

compare this folder to tests that were

created without a testing framework but

now that the lesson's over we're going

to rename test- Jasmine to just test to

make it more

standard first we need to rename this

folder up here so we'll right

click

rename and let's rename it to test-

simple because this folder contains

tests that were created without a

framework let's press enter

and now we can rename test- Jasmine to

test by right clicking

rename and rename it to tests and press

enter another thing we can do is we're

going to drag test- simple into the test

folder so that all of our tests are

contained in one

folder so if it asks you to update the

Imports you can click yes

and we also need to open money test.js

in the test- simple folder because it

updated the Imports and then save this

file finally we're going to run all of

our tests again to make sure everything

still works after we move things around

so because test.html is inside a

different folder now we need to reopen

this with live server

so we'll rightclick and click open with

live

server and it'll show us that all the

tests are still passing so our code is

still

correct so now we can close some of

these extra tabs

here and save our changes into git we'll

open the git

section and all of these changes are

related to renaming the folders

so we'll give a message at the

top rename test- Jasmine

folder to

tests and

commit and that's the end of this lesson

in this lesson we learned how to test

our code using manual and automated

tests we learned how to organize our

test using test cases and test Suites we

learned how to use a testing framework

like Jasmine to help us write tests

easier we learned how to Mock and spy on

methods we learned how to test web pages

using integration tests and we learned

about hooks which lets us share code

between our

tests here are some exercises to help

you practice what we learned in this

lesson e

in the rest of this course if you get an

error in your project but your code

looks correct you may have some bad data

saved in local storage to fix this you

can try running local storage. CLE in

your console to remove everything from

local

storage and then refresh the

page if you see an error like this

object object that means that you saved

something directly into local storage

but you have to jason. stringify it

first so check your code to make sure

that you're always stringifying before

saving to local storage and then clear

your local storage and refresh the page

in this lesson we're going to learn

objectoriented

programming objectoriented programming

or oop is another style of programming

so it's another way that we write our

code it's useful to know because many

programming languages use

oop now how do we use objectoriented

programming object-oriented programming

is basically organizing our code into

into

objects let's look at an

example we're going to go to our

code and we're going to scroll up and

open data/ cart.

JS inside this file we have the code for

our cart and you'll notice that for the

cart we have some data at the top and

then we have a bunch of functions at the

bottom that modify the cart and these

are separate from each other the data

and the functions so this style of

programming that we've been using

throughout this course is called

procedural programming procedure means a

set of step-by-step

instructions and this is basically a

function so in procedural programming we

organize our code into separate

functions like we did

here on the other hand in objectoriented

programming we organize all of this code

into an object so we put everything

together into an

object so let's do an example and

convert this cart code into

objectoriented

programming we're going to click cart.

JS and inside this folder we're going to

create a new file by clicking

here and let's name this file

C- oop or objectoriented

programming. JS and press

enter and now we're going to copy all of

the code in cart into this new file so

let's open this and we'll click in this

file and then we'll type control a or

command a to select all the code and

then right click

copy and inside C- oop we're going to

rightclick and paste

and let's scroll back up to the

top and now to convert this code into

objectoriented programming we're going

to group all the data and the functions

together into an object first at the top

let's create an object that we can put

all of these inside

of so we'll create a variable const

let's call it cart equals and object

and now we're going to group our data

and all of our functions into this

object so let's do it step by step and

we'll start with this cart

variable as a reminder cart semicolon is

actually a shortcut for cart equals

undefined to make things easier to

understand let's actually write this out

in full instead of using the shortcut so

we'll type cart equals undefined

and now we're going to move this into

the object so we'll select this

line and then

rightclick

cut and then inside the object we're

going to rightclick and

paste now inside an object we can't use

the word export or

let so to move a variable into an object

we're going to convert it into a

property and a value so we'll remove

these

words and then type cart and colon

undefined and remove the semicolon and

replace it with a

comma so this is the same thing as cart

equals undefined but we move that value

into an

object now one problem here is that if

we access this cart property we're going

to do cart. cart which can be a bit

confusing so let's actually rename this

property to cart capital I items instead

to make it a bit more clear that this

contains the items in the cart or the

products that are in the

cart next we're going to group all of

our functions into this object as well

so let's create some new

lines and we're going to move this

function inside here so let's select

this

function and then

rightclick

cut and inside the

object we're going to

rightclick and

paste and again we can't use the word

export inside an object so we're going

to convert this into a property and

value as

well so let's remove these words

and let's make the property name load

from storage and then we'll type a colon

and we'll make the value a

function brackets and curly

brackets so that's how we move a

function into this object now make sure

that you use a regular function syntax

here and not an arrow function and I'll

explain why later in this

lesson now as a reminder when we have a

function inside an object

we call this a

method also JavaScript has a shortcut

for methods called the shorthand method

syntax so instead of typing colon and

function we can actually just remove

this

code and just type brackets and curly

brackets after the function name and

this is a shortcut for the code that we

had

before now the code inside this function

doesn't actually work anymore because

cart was actually renamed to cart items

so we have to rename this variable so

instead of cart we're going to do cart

dot cart

items to access this value and same

thing here cart do cart

items and here cart

doart

items so so this code Works however we

have a small problem here if we change

the name of the object up here this code

will no longer

work to solve this problem JavaScript

has a feature called this this gives us

the object that contains this function

so it gives us this outer object up here

so to improve our code we're going to

change from using a variable named cart

to this and here as well this. cart

items and this Dot card

items so this will give us the outer

object and now this code will always

work and it doesn't matter what the

variable name

is the last thing we're going to change

in this function is we're currently

loading from local storage

cart however our original cart was also

loading from local storage cart so let's

actually change this to C- oop so that

we don't affect our original

cart let's move on and we're going to

move the other functions into this

object so let's go down to the next

function which is save to storage we're

going to select this and then

rightclick

cut and then inside this object at the

end we're going to add a comma and some

new

lines and we're going to rightclick and

paste and we can't use the word function

at the front here so let's remove this

word and just use the shorthand method

syntax so this is a shortcut for colon

function and here we're saving to local

storage cart

so let's also change this to C- oop so

we don't affect our original cart so

we'll change it to card-

oop another thing we need to change is

that the cart was renamed to cart

items so here we're going to change from

cart to this which gives us the outer

object and then dot cart items

which is this property so it should do

the same thing as before except this

function is now inside an

object let's continue and move another

function into the object so we're going

to do add to cart this time so let's

select this

code and then

rightclick

cut and inside the object we're going to

add a comma and some new lines and then

rightclick and

paste so again instead of using export

function we're just going to remove this

code and use the shorthand method syntax

which is a shortcut for this

code and now let's update the code

inside this function as well so instead

of the cart we rename this to this. cart

items so we'll change it to this do cart

items

and then down here we're going to change

from cart to this. cart

items and also the function save to

storage was moved inside the object so

now to access this function we're going

to get the outer object again using this

and then dot save to storage so down

here we'll add this dot in front to

access the function inside the

object and now let's move on and move

the next function into the object so

we'll select this

code and then

rightclick

cut inside the object add a comma and

some new lines and right click and

paste we'll remove export

function and use the shorthand method

syntax and again we'll change from cart

to this. cart

items we're going to change cart here to

this.c cart

items and change save to storage to this

do save to

storage so we access save to storage

inside this

object next let's move this last

function into the object so we'll select

the code and then rightclick

cut and inside the object we're going to

type a comma and some new lines right

click and

paste we'll remove export function and

use the shorthand method

syntax and update the code in this

method so we'll change cart to this do

cart

items and save to storage to this Dove

to

storage now let's remove the extra

lines and the last thing we need to

update is that load from Storage was

moved inside the cart object so to

access this function at the front we're

going to type

cart. load from storage and save this

file and that's it this is the basic

idea behind objectoriented programming

we organize our code into objects so we

group the data and the functions

together into an object like

this now let's talk about why do we use

objectoriented

programming objectoriented programming

tries to represent the real

world in the real world a cart is a

physical object object so in

objectoriented programming we represent

this physical object as a digital object

or in this case a JavaScript

object a physical cart can have products

inside so our JavaScript object can also

have products

inside a physical cart also has actions

we can take to modify the cart like we

can add a product or remove a product

our JavaScript object also has actions

we can take to modify the cart like the

add to cart function or the remove from

cart

function so as you can see

objectoriented programming tries to

represent the real world we take a

physical object like a cart and

represent it as a digital object like a

JavaScript

object and some people feel feel that

this makes the code more intuitive or

easier to

understand now let's try out the code in

this object to make sure it actually

works we're going to scroll down to the

bottom and

here we're just going to type

console.log the

cart and save this

file and now let's load this code into

the project to do that we're going to

open the scripts folder and open the

file checkout.

JS and at the top below the Imports

we're going to import our new file so

let's type

import and we're going to use a slightly

different syntax we're just going to

type a

string and give it the file that we want

to load so we need to load C- oop. Js

so first we need to get out of the

scripts folder using do slash and then

go into the data folder data slash and

load C-

oop.

JS so this is another syntax we can use

for imports this just runs all the code

inside this file without importing

anything which is what we need in this

situation so let's save this file

and then open this page in the browser

so if you don't have this page open you

can scroll down to checkout. HTML and

then right click and open with live

server I already have this page open so

I'm just going to open that

Tab and if the page is too big we can

zoom out by pressing control minus or

command minus a few

times and now let's check the console to

see what the cart looks like on this

page we're going to

rightclick and click

inspect and then open the

console and in the console we'll see

this cart object so inside this object

we have the data as well as all the

functions for our cart but it's grouped

inside an object and you'll see that the

code still works the same as before cart

items has a the two default

products if we look at our code and open

card-

o at the beginning we run cart. load

from storage and then inside this

function if we scroll up it will give

the cart items this default cart with

two products inside and that's what we

see in the console

here so we know that the code inside

this object still works works the same

way as

before so now let's try another method

to make sure that it's working so let's

try using the add to cart method to add

a product to the cart items up here so

we'll scroll

down to the bottom and then above

console.log cart we're going to call add

to cart now add to cart was saved inside

this cart object so to access it we're

going to type

cart. add to cart and

brackets now add to cart takes one

parameter which is a string and this is

the product ID that we want to add so to

find a product ID we can go to the data

folder and products. JS and then inside

here we have this list of products so

let's actually scroll down to the third

product which is right here so this

t-shirt product and we're going to add

this product ID to the cart so let's

select this ID we're going to

rightclick

copy and then inside C-

oop inside the string we're going to

rightclick and paste that product

ID and let's

save and let's check the console

so I'll open the console

Here and Now inside the cart object if

we expand it cart items now has three

products because we just added a new

product to the cart so this shows that

all of the code is working the exact

same way as before we just organized it

into an object and that's objectoriented

programming now that we're done with

this example let's remove these two

lines of

code and

save next another reason we use

objectoriented programming is it's easy

to create multiple objects for example

the real amazon.com has a feature called

Amazon business where you can have a

separate cart for your business

purchases so how do we create two

separate carts in our code with

objectoriented programming this is easy

we can just make a copy of the cart

object so we can scroll up in this

code and I'm just going to click this

Arrow here beside the card variable to

collapse this code and to create a

separate cart for business purchases

we're just going to select this code and

then right click

copy and at the

bottom right click and

paste and now we have two separate cards

so let's scroll up to the top of the

second cart which is right here and we

said that we wanted this card for

business purchases so let's rename this

to

business Capital C

cart and when we load from Storage let's

load it from cart Das business instead

so that it doesn't conflict with the

cart up

here and if we scroll down same thing in

save to storage let's save this cart to

cart Das

business and finally let's scroll down

to the

bottom and here instead of cart. load

from Storage we're going to change this

to business cart. load from Storage

and that's it we just created a

completely separate cart simply by

copying this object so object-oriented

programming makes it easy to create

multiple

objects so now let's console.log both of

these cards to see what they look like

we're going to scroll to the

bottom and here we're going to

console.log the

cart and

console.log the business cart and

save and if we open the console for the

checkout

page it will show us that we have two

carts the regular cart has three

products inside and the business cart

has two products inside and these are

just the default products that we get

when we first load the cart

so you can see that these two cards are

completely separate from each

other in the real world we can have two

physical cards that are completely

separate from each other and in

programming we can also have two cards

that are completely separate from each

other by simply making a copy of the

object so again object-oriented

programming tries to represent the real

world

now currently there's an obvious problem

with how we're creating multiple objects

which is we're copy pasting a lot of

code and this can make our code messy

and hard to manage so now we're going to

make our code cleaner by using a

function to create multiple

objects so first let's delete this

business card that we copy pasted so

we're going to select this

object and then up to here the business

card we're going to remove

it and now instead of copy pasting this

object we're going to use a function to

generate these objects so at the top of

this file let's create a new

function and we'll name it capital c

cart brackets and curly

brackets so by the way in objectoriented

programming a naming convention is to

use Pascal case for things that create

or generate objects in Pascal case we

start every word with a capital

including the first word so that's why

we started cart with a Capital

C now inside this function we're going

to create cart

objects so let's actually move this

object into the function so we can

create it using the function so we're

going to select this object to here and

then we'll right

click and cut

and then move it into the function by

clicking in the function and then

rightclick and

paste so now every time we run this

function it will generate a new cart

object and we don't have to copy paste

this code over and over to create

multiple

objects so at the bottom I'm going to

click this Arrow to collapse this object

for now and at the bottom of this

function we're going to return this C

object so we can use it outside the

function okay now let's give this a try

and we'll use this function to generate

cart objects so first let's create the

normal cart using const cart make it

equal and we'll run this function to

generate an object Capital C cart and

brackets and let's generate another

object using the function using const

and we'll name it business

cart equals Capital C cart and

brackets and we'll still load from

storage for both of these and then

console log both of

these so basically instead of copy

pasting all the time we're going to use

a function to generate

objects so now let's

save and then open the

console and and now we have two cart

objects

again however now both of these carts

have three products

inside but before the regular card had

three products and the business card had

two

products so what

happened if we go back to our code and

look inside this cart

object you'll notice that we're loading

from the same key in local storage which

is C- o that means every cart that we

generate will be getting its data from

the same place in local

storage so to fix this we're going to

replace C- oop with a parameter so

different carts can use a different key

in local storage so at the top let's

create a parameter called local storage

key and then instead of using the same

string every time we're going to use the

parameter local storage

key and the same thing for save to

storage instead of saving to the same

key every time we're going to replace

this with the parameter local storage

key and finally when we run this

function at the bottom

here we need to give the function a

local storage key so for our regular

cart let's use the string cart C-

oop and for the business cart we can use

a different key like the string cart Das

business so now these two carts will

load from different keys in local

storage and they can have different data

so let's save and then check the

console and now our regular card has

three products and our business card has

two products like

before so let's go back to our code and

this is a better way to create multiple

objects instead of copy pasting a bunch

of code every time we can create a

function that generates

objects so now let's save this example

into git we'll go into our git

section and then at the top here we

created a function to generate these

objects and in checkout. JS we are

loading that c - oop practice file so

we'll type a message to describe these

changes create oop or objectoriented

programming version of cart and

commit next we're going to learn an even

better way to generate objects

object-oriented programming has a

feature called a Class A Class is

specifically designed for generating

objects a class is basically an object

generator So currently if we open our

code and then open C-

oop we learn how to use a function to

generate objects in objectoriented

programming so now we're going to switch

this to using a class to generate these

objects instead because classes are

cleaner and have more features than

using a function so first let's create a

new file for learning

classes inside the data folder we're

going to click C- oop and then create a

new

file and we'll name this file cart DCL

class. JS and press enter

so first let's copy over all the code so

we can compare it we're going to open C-

oop click this file and then press

contrl a or command a to select the code

and right

click

copy and in

C-Class we're going to right click and

paste and we'll scroll to the

top and at the top we're going to create

our first class class using the word

class and now we're going to give a name

to this class so let's name it the same

as here Capital C cart and then curly

brackets as a reminder a naming

convention is to use Pascal case for

things that generate objects so that's

why we start this cart with a Capital

C so this is a class A Class is

basically an object

generator so now inside the class we're

going to put the properties and methods

that we want for each object that we

generate so here we have our properties

and methods we're just going to move

them into the

class so first let's select the card

items

property we're going to right click

cut and then move it into the class by

clicking in here and then right click

and

paste and classes use a slightly

different syntax than objects so to

create a property called cart items

we're going to type the property name

and instead of a colon we're just going

to make it equal to undefined and

instead of a comma at the end we're

going to put a

semicolon so that's how we add a

property to a class and now every object

that we generate will have this property

just like we did

before next let's move the methods into

the class so we'll delete these lines

for now and we'll move load from Storage

so we'll select this method and then

rightclick and

cut and inside the class we're going to

move it by right clicking and

paste and classes use a slightly

different syntax to create methods as

well so instead of having a comma at the

end we can just remove it and every

object that we generate will now have

this

method so now let's move the rest of the

methods into this class we're going to

scroll down and we'll move save to

storage so we'll select the method and

right click

cut and at the bottom of the class we're

going to right click and paste

and remove the comma at the

end same with add to cut we'll select

this

method and then right

click

cut and inside the bottom of the class

we're going to rightclick and

paste and remove the comma at the

end as well as remove from cart so we'll

select this

method right click

cut and at the bottom of the class right

click and

paste and remove the comma at the

end and finally we'll move the last

method update delivery

option and right click

cut inside this class we're going to

right click and

paste so this method did not have a

comma at the end so this looks

good so that's how we create a class we

basically give it some properties and

methods and now when we generate objects

using this class every object that we

generate will have these properties and

methods now one thing we need to fix

here is that local storage key doesn't

exist anymore to fix this we're going to

save this in a property instead so at

the top

we're going to give a new property to

every object that we generate called

local storage key and make it equal to

undefined to

start and then inside the methods we're

going to switch this to this. local

storage key so this is going to point to

the object that we generate just like

before and then local storage key will

access this property

and another place we need to fix this is

inside save to storage so instead of

using a variable local storage key we're

going to use the property this. local

storage

key and that's it so if we scroll

down we basically converted this whole

function into a class so now we can

remove it

and the final step here is now that we

have this class let's use it to generate

these two objects

again to do that instead of this code

we're going to type the word new and

then type the class name which is

capital c cart and

brackets so you see that a class uses a

similar syntax as a function except we

use the word new in front of

it so this generates a new object using

our

class and this new object will have all

the properties and methods that we added

above so let's do the same thing for the

business card we'll use the class to

generate it we'll remove this

code and then we'll type new and the

class name Capital C cart and brackets

to generate another object using this

class now there's one thing we need to

fix here each of these objects has a

property called local storage key and

they're currently undefined so we need

to set this

property so at the bottom here we're

going to type

cart. local storage key and we'll make

it

equal and we'll use the same string as

before which is C-

oop and we'll do the same thing for the

business cart we'll type the

business

cart. local storage

key and make it equal the same string

that we had before which is cart Das

business and then we'll load the cart

from Storage as well as the business C

from storage and we'll console.log

them so we have the same code as before

except we converted it from a function

to a

class so now let's

save and we're going to run this code So

currently if we go into our code and

open checkout.

JS we're still loading C-

oop so we're just going to update this

and load

C-Class instead and

save and we'll open cart Das class

again and now if we open the

console you can see that we created two

cart objects just like we did

before and the regular card has three

products inside and the business card

has two products

inside and if we click this Arrow beside

prototype we can see the methods that

each of these objects have

so we're basically creating the same

objects that we had before except this

time we used a

class by the way each object that we

generate from a class is called an

instance of the

class we can also check if an object is

an instance of a class using the code

business cart and then instance of and

then the class name name Capital C

cart so this will check if this object

was generated from this class so we can

console.log this result

console.log and close bracket and

save and then check the

console and it will tell us that this is

true so business card was generated from

this

class okay don't worry if class are a

bit confusing at first just remember

that objectoriented programming means

organizing our code into objects because

this tries to represent the real

world and then classes are a feature

that help us generate these objects so

they make it easier to create these

objects a class is basically an object

generator

now that we learned how classes work

let's talk about the benefits of

classes if we scroll

up when we generate an object it's going

to have these properties and these

methods and you'll notice that a class

actually looks like the object that we

generate and this is cleaner than using

a function like we had before

another benefit of classes is that they

have extra features for object-oriented

programming the first feature is called

a Constructor which lets us run some

setup code after creating an

object so if we scroll down in our

code you'll notice that after we create

these objects we run some setup code a

Constructor lets us put the setup code

inside the class and this makes our code

cleaner because we can group everything

together inside the

class to create a Constructor we're

going to scroll up in the

class and Below these properties we're

going to create a new method called

Constructor brackets and curly

brackets so the Constructor method works

like a normal method we can put code

inside and it will run the

code but the special thing about the

Constructor is that when we generate an

object it will run this Constructor

automatically so this is a great place

to put our setup

code so let's scroll down to the

bottom and here instead of running the

setup code outside the class we're just

going to move this into the class and

into the Constructor so we'll select

this code

and then right click

cut and scroll to the

top and inside the Constructor we're

going to rightclick and

paste so now after we create an object

it will run the code in the Constructor

and set up the

object so there's a few things that we

need to fix here the first thing is each

object object that we create is going to

run the Constructor so we only need one

of each of these lines so let's remove

the setup for the business

card so now the setup code has two steps

we set the local storage key and then we

load from Storage the next problem is

that the object that we create is not

going to be called cart every time

to solve this we can replace cart with

this and here as well this. load from

Storage so as a reminder this points to

the object that we generate so whatever

object that we generate we're going to

get its local storage key and set it and

we're going to get its load from Storage

method and run that

method now the second problem here is

that we don't want local storage key to

be card- oop every

time to fix this the Constructor can

also have parameters let's give the

Constructor a parameter and we'll name

it

local storage key and instead of the

same string every time we're going to

use local storage

key now the last thing is how do we save

a value into this parameter

so if we scroll down to the

bottom when we call the class between

these brackets we can put the parameters

for the Constructor so for the cart we

want the local storage key to be the

string C- oop and for the business cart

we want the local storage key to be the

string cart Das

business so the values inside here are

saved in the parameters in the

Constructor so C- oop will be saved

inside local storage key and then we use

it and then the same thing for cart D

business so now let's save this

code and then open the

console and you'll see that the cart

objects are correct so after we

generated each object we also ran this

setup code so that's how the Constructor

works every time we generate an object

it will run the code inside here so this

is a great place to put setup code and

make our code

cleaner so here are a few more details

about the

Constructor the method has to be named

Constructor we can't just use any name

that we want we also should not return

anything from a

Constructor so last ly a shortcut that

we can use in a class is when we have a

property and it's equal undefined we can

actually remove equal undefined and just

use a semicolon so this is the same

thing as the code before and same thing

here we can remove equal undefined and

just use a semicolon and

save so we finished converting our code

from using a function to using a class

and as you can see a class is just a

better way to generate objects in

objectoriented

programming so now let's save our code

into git we'll open the git section

inside cart Das class we created our

cart class and inside checkout. JS we're

basically loading the cart Das class

file so we'll type a message to describe

this change create

class

version of cart and

commit next we're going to learn an

important feature of classes called

private properties and

methods so let's open our code again and

open

C-Class and you'll see that this class

has a property called local storage

key so this property is useful inside

the class but it's not really meant to

be used outside the class for example at

the bottom

here we could take this

object cart and then change the local

storage key using dot local storage key

equals something

else now this is a problem because it

will mess up how this object works and

it will start saving to a different

local storage key so this is a common

problem in programming where if you're

working on a team somebody might

accidentally change properties that

they're not supposed to to prevent this

classes let us make a property or a

method private which means it can only

be accessed inside the

class so let's remove this line

and scroll

up and to make local storage key private

we're just going to add a number sign in

front or a

hash and also whenever we access this

property inside the class we're going to

add the hash in front so we'll type

this. has local storage key this.h local

storage key and inside save to storage

this.h local storage

key so this is called a private property

this means it can only be used inside

this class or inside these curly

brackets it cannot be used outside the

class a property without a hash in front

is called a public property meaning it

can be accessed

anywhere so now let's

save and open the console

and the code still

works so we made this property private

and we're able to access it inside the

class so now let's try accessing this

property outside the class to see what

happens we're going to scroll

down and we're going to try to access

cart. hash local storage key

and change it to something else like

test and

save and if we open our

console you'll see that when we try to

access a private property here it will

give us a syntax error saying this is a

private field and by the way a field is

the same thing as a

property so that's how a private

property works it prevents us from

accessing this property

outside the object and messing it

up we can also have private

methods so let's remove this

line and scroll

up and the method load from Storage

should also only be used inside this

class there's really no reason for code

outside to be calling load from Storage

so to make our code safer we're going to

make this a private

method to make a method private we're

going to do the same thing in front of

the method we're going to add a number

sign or a hash and we're going to update

the rest of our code so we're going to

do this dot hash load from

storage and now we can

save and check the console to make sure

that everything is still working so

everything still looks good

because we're only using this private

method inside this

class so a class Let's us create private

properties and methods and this is

useful on a bigger project where people

might not be sure which properties and

methods they're supposed to use outside

the class and which ones to

avoid so now let's save our changes into

git we'll go into the git section and

inside here we we made local storage key

and load from Storage

private we'll create a message to

describe these changes make local

storage key and load from Storage

private and

commit now that we learned

objectoriented programming and and

classes we're going to use it in our

project so one thing we could do is to

take this card class and replace

everywhere we use cart in our project

however we use cart in a lot of places

and this would take too much time so I'm

going to leave replacing the cart as a

challenge

exercise instead we're going to work on

the

homepage so first let's go back to our

code and we're going to open checkout.

JS and we're just going to comment out

this import because we're just using

this file for practice so let's save

this and then let's open the checkout

page so I already have it open if you

don't have it open you can rightclick

checkout. HTML and open with live

server on the checkout page we're going

to click this icon in the top left to go

to the

homepage on this page we have a list of

products

here and the code for these products is

if we go back to vs

code and on the left side we're going to

open

dataproducts

DJs so here is the code or the data for

all the products on the homepage and

you'll notice that each product is an

object we're going to learn a technique

called converting an object into a

class so what this means is instead of

using regular objects in this array

we're going to use a class to generate

these objects so Above This array let's

create a new class using the word class

and let's call it capital P product and

curly brackets

because this class is meant to generate

products so now each of our products is

going to have some properties like the

ID image and the name so let's add these

to the class We'll add the ID property

and a semicolon so that it starts off as

undefined and then an image property and

a name

property and each product will also have

a rating and the price sets rating and

price

set and you'll notice each object here

also has a property called keywords now

we're not currently using this in our

project so we're going to leave it out

of the class for now and if we need to

use it later we can always add it back

in so now we have all the properties

that we want for each product so now

let's test this by generating a product

using this class so that here

let's create a variable const product

one equals and to generate an object

we're going to use the word new and then

the class name capital P product and

brackets and let's console.log this to

see if it worked

console.log product one and

save so now we're going to open the web

page and then open the console so right

click and

inspect and open the

console and inside here you'll see that

we created a product object using the

class so right now all of these

properties are undefined so now let's

set the values of these properties we'll

go back to our

code don't follow along here but one way

to set set these prop properties is to

access them outside the

class for example product

1. equals something and then do product

1. image equals something and then

product one. name and so

on so this is not a good way to set

these properties because we have to do

this for each product that we create so

it makes our code repetitive and messy

instead notice that when we create a

product this is kind of like the setup

code we create a product and then set

all of its

properties and remember classes have a

specific feature for setup code called

The

Constructor and now you can follow

along so inside this class we're going

to create a

Constructor brackets and curly brackets

so whenever we generate an object it's

going to automatically run this

Constructor so this Constructor is where

we should put our setup

code so let's remove this

code and then do all of that inside the

Constructor so first we want to set the

ID property we're going to do this do ID

and make it equal and now what value do

we set the ID to so the value of the ID

is inside each of these

objects so when we create a product up

here we're going to put this object

inside these

brackets and then that's going to go

into the Constructor in here so in the

Constructor let's create a parameter to

save this data so we'll name it product

details and now to save something inside

ins this parameter we're going to put it

between these

brackets so let's actually give this

entire object to the

Constructor so we're going to right

click and

copy and then between these brackets

we're going to rightclick and

paste so whenever we create a new

product we're going to give it this

object with all the details

it's going to get saved in here and now

we can set the

properties so this. ID is going to be

equal to the product details. ID

property so product

details.

ID and for the image we're going to do

this. image equals the product details

which is this object that we passed in

dot the image

property same thing for the name so this

do name equals product

details. name which is this property

here same thing for the rating this.

rating equals product details.

rating and finally the price

sense this. price sense equals the

product

details. Price

sets so this is called converting an

object into a class what we're doing is

we're basically taking a regular object

like this we put it inside a class and

then we copy over the

properties you can also visualize it

like this we have a regular object and

we're basically wrapping it inside a

class and the reason we do this is that

classes have extra features we can use

like we can add methods and we can also

have private properties and private

methods so we basically have these same

object as before except we have an

enhanced version of that object it has

some extra features from

classes so for now let's save this code

and then down here we console.log

product one so let's take a look at it

in our console so we'll open the

console and now we can see that we

created a product object so it's the

same object as before except now it's

enhanced it has some extra features from

classes so next we're going to take this

technique and apply it to this entire

array so instead of having an array of

regular objects we're going to convert

each of these objects into the product

class now one way we could do this is

that in front of the object we can just

type new product Open Bracket and then

close bracket at the

bottom and this will essentially convert

this regular object into the product

class however we're going to have to

repeat this code for every object in the

array and it's going to be a lot of work

and

repetition so instead let's just Loop

through this array and then use code to

convert each of these objects so instead

of typing this out manually we're going

to remove this and remove the round

bracket at the end and then I'm going to

click this Arrow beside the array to

collapse

it and at the end of the array we're

going to use an array method called do

map and

brackets so map basically Loops through

an array and for each value it runs a

function so we're going to give this a

function that we want to run for each

value so arrow and curly

brackets and this inner function is

going to get a

parameter so this parameter is basically

each value in the

array so it's going to take the first

value and then save it inside this

parameter run the function and then take

the second value save it in here run the

function third value save it and run the

function so let's name this parameter

the product

details because each object in this

array contains product details so now

it's going to take each object save it

in the parameter and run the function

and here we're going to convert the

object into a class to do that we're

going to use the code new capital P

product

brackets and we're going to give it this

regular object which is the product

details and now there's a second part to

how Map works so map creates a new array

and whatever we return from this inner

function is going to go inside that new

array so here we're going to return this

class so this result is going to be put

inside a new array so you can think of

map as we take each value in an array we

run this function on it and we transform

it and then put it inside a new

array so here we're essentially

transforming each of these products or

these regular objects into a

class so at the bottom let's

console.log the products array to

confirm this so we'll

save and open the

console and now you can see we have an

array and each of the values is a

product class instead of just a regular

object

so we converted all of our products from

regular objects into this product class

and now let's open the web page to make

sure that everything still

works so if we open the

page you notice that everything is still

working

correctly and that's because we have the

exact same objects as before except

they're now just sort of enhanced

objects next let's use those extra

features of classes to simplify our code

for this page we'll go back to our

code and on the left side let's open

amazon.

JS so this is the code that creates the

homepage so in here we're going to

scroll down until we see the rating

section where we calculate the stars and

the rating

account so notice that inside our HTML

we're constru in this URL here for the

number of stars a product

has and we're also creating the price

that we want to display on the

page now instead of doing this all in

the HTML our code would be cleaner if we

moved this logic into our class because

we want to group this related code

together so let's use the features of

classes to make this code a little bit

cleaner we'll open products. Js

and we'll scroll up to the product class

and inside here let's add some methods

for calculating the stars and the

price so we're going to add a method and

call it get Stars URL brackets and curly

brackets and let's create another method

called get price brackets and curly

brackets

and now we're going to move the code

from our HTML into this class so we'll

open amazon.

JS and then here we're creating the URL

of the Stars so let's actually select

all this

code and

rightclick

copy and inside products.

JS inside get Stars URL we're going to

rightclick and paste

and this is going to be a string so at

the front let's add a back tick so we're

going to use a template string because

we're going to insert a value inside and

at the end we'll add another back

tick so now that we created the string

we're going to return it from this

method so

return and semicolon at the

end and one thing we need to fix is that

product is not defined anywhere so to

get the rating property of whatever

object this is we're going to use this.

ratings.

Stars so now each product is able to

construct its own Stars URL here so

let's save this

file and then inside amazon.

JS instead of doing this calculation

directly inside the HTML

we're going to delete it and we're going

to insert the

product. getet Stars URL method and

brackets so you'll notice that we have

the same product object as before but

now it's sort of an enhanced product we

can add methods to group related code

together and make our code

cleaner let's do the same thing with the

price down here we're going to calculate

this using the method instead of

directly in the

HTML so we're going to select this code

and then right click

copy inside products.

JS inside the get price method we're

going to

rightclick and

paste and again we want to return the

price as a string so at the front we'll

create a template string because we're

inserting a

value and at the back a template string

or a back tick and we're going to return

this from the

method and another thing we need to fix

is that product is undefined so to get

the price sets property we're going to

use this Price

sets now one extra thing we need to do

here is that we're using the format

currency function but we didn't import

it so we're going to scroll to the

top and import format

currency import curly brackets the

format currency function from a

string and here we're going to locate

this function so we're inside the data

folder we need to get out of the data

folder using do slash and then go into

the scripts folder into the UTS folder

and load money. JS so scripts SL

utils

money.jpg

and instead of calculating the price

inside the HTML we're going to remove

this and then insert the

product. getet price method and

brackets so now let's

save and let's open the homepage to make

sure that it's

working so now you see that everything

is still working including the stars and

the

prices so we'll go back to our

code and now that we have these methods

let's use them in our other page which

is the checkout page so we'll open

scripts

checkout.

JS and this basically displays the

products on the checkout

page if we scroll to the HTML and find

the delivery date the product image and

the product name we're going to see that

here we're also calculating the

product's price directly in the

HTML so instead of doing this let's use

the method we just created so select

this code and remove it and insert the

matching product this time so

matching

product and remember we converted all of

our products into classes so this is not

a regular object anymore it's more of an

enhanced object it's a product

class and that means this will have the

method. get price and brackets and Save

so now let's open the checkout page to

see if this works we'll open the web

page and then at the top right we're

going to click the

cart and now you can see that on the

checkout page the price is still

displayed

correctly and that's it if we go back to

our

code you'll see that by converting our

objects into classes we're able to use

extra features of classes like methods

to make our code

cleaner so now let's make sure that all

of our tests are passing we'll go to the

left and scroll down and we're going to

open test.html in the browser so if you

don't have it open you can right click

and open with live server but for me I

already have it open so I'm going to

open the test page and all of our tests

are still passing so our code is still

correct and now now let's save our

changes into git we'll open the git

section and in products. JS we created

the products class and at the bottom we

converted all of our objects into the

products

class so actually one thing I forgot to

do is to clean up these console. logs so

let's do that right now we're going to

open our code and go into products.

JS and we'll scroll down right after the

product class and let's remove this

product one because it was just an

example and we'll also remove the

console.log products at the

end and

save so now if we go back into git and

open products. JS we just have the code

where we convert our objects into a

class in amazon.

JS we use the feature of classes called

Methods to make our code cleaner in

checkout. JS we stop loading our cart

class practice file and in orders

summary. JS we also use a method to make

our code

cleaner so now let's create a message to

describe these

changes

convert products into classes and commit

next we're going to learn an important

feature of object-oriented programming

called

inheritance inheritance lets us reuse

code between

classes so first let's learn the concept

of

inheritance to do that we're going to

open our

project so we'll open this page here to

our checkout page

and we're going to go to the homepage by

clicking the top

left and on this page we have a bunch of

products but you also notice that we

have different types of products for

example we have clothing like this

t-shirt and we have appliances like this

toaster so clothing and appliances are

still products they have a name a price

and a rating but they are a more

specific type of product for example

clothing can have all the properties of

a regular product but it can also have

specific properties like a size

chart so how do we represent this kind

of relationship in our code we have a

product and then we have a more specific

type of

product one way to represent this is to

create a new class called clothing and

this class will have all the properties

of a regular product but also more

specific

properties however there's a problem

with this which is we're duplicating a

lot of

code instead objectoriented programming

has a feature called inheritance that

allows one class to get all the

properties and methods from another

class so we don't have to copy paste

this

code for example we can make a clothing

class and then use inheritance to get

all the properties and methods from the

product

class this is similar to how a child

inherits things from their parents like

their hair color or the shape of their

eyes in fact we call the product class

the parent class and we call the

clothing class the child

class so now let's learn how to use

inheritance in our code we're going to

open VSS

code and open our code on the left and

then open products.

JS and we're going to scroll to the

product class and then below this class

we're going to create a more specific

type of product called

class and capital c

clothing and curly

brackets so we said that clothing is is

just a specific type of product so that

means clothing should have all the

properties and methods of a

product so first let's inherit all these

properties and methods into the clothing

class to use inheritance after the class

name we're going to use the word

extends and then we're going to give it

the class that we want to inherit from

which is the product class

Above So this means that clothing will

get all the properties and methods of

this class or it will inherit all the

properties and

methods to demonstrate this let's leave

this empty and create a new clothing

object so down

here let's create a variable first using

const and we'll name it a

t-shirt make it equal

and we'll generate a new clothing object

to do that we'll use the word New

Capital C clothing and

brackets and next we're going to expand

the products array and we're going to

give the product details to this class

so we're going to scroll down to the

third product which is the

t-shirt and we're going to select this

object

and then right

click

copy and scroll

up and now between these brackets we're

going to right click and

paste so now we created a new closing

class we gave it all the data that it

needs and let's console.log it to see

what it looks like so down here we're

going to

console.log brackets and the variable

name which is t-shirt so here

t-shirt and

save and now let's open the console so

we'll open our web page and then on this

page we're going to right

click

inspect and open the

console and you'll see that we created a

new clothing

object and if we open it you'll see that

this has the same properties as the

product class

so this inherited all the properties

from

product so let's see if we inherited the

methods as well we'll go to our

code and let's try the method get price

so we'll

console.log

t-shirt. getet price and

brackets and

save and now if we open the console

again you'll see that get price also

works so clothing inherited the methods

from product as well so even though this

is empty this class gets or inherits all

the properties and methods of

product so we use inheritance when we

have one class which is a more specific

type of another class for example

clothing is a more specific type of

product we want all the properties and

methods of the product still but we just

don't want to copy paste all this code

down here so inheritance lets us reuse

code between

classes so now that we have this

clothing class we can add properties and

methods that are more specific to

clothing for example clothing can have a

size

chart so for con convenience inside this

t-shirt object I've actually added a

size chart link so let's add this to our

clothing class so up here we're going to

add a

property size chart

link and now to set this value we're

going to use the Constructor like we did

before so down here we're going to use a

Constructor brackets and curly brackets

and we're going to give this a parameter

called Product

details so when we create the clothing

we save this object into product details

and then we can use it to set the

properties up here so we're going to do

this do size chart link and make it

equal to the product details

which is this object and we're going to

get the size chart link

property dot size chart

link now one problem we have here is

that clothing inherits all the

properties from the product so we also

need to set the ID the image the name

and so on so if we scroll down we could

do something like this . ID equals

product details.

ID however instead of doing this one by

one all over again inheritance gives us

a shortcut we can actually just use the

Constructor in the parent class up

here so to call the parents Constructor

we're going to use a special feature of

classes called super and brackets

so super basically calls the Constructor

of the parent class which is the product

so this will call the Constructor up

here and we also need to give this the

product details so down here we're going

to call Super and give it the product

details so this will call the

Constructor of the parent class which is

product and that will set the ID the

name and the rating

so now let's save

this and check our console

again and open up the clothing object

and you'll see that now we have a size

chart link

property so that's how inheritance Works

a class can get or inherit all the

properties and methods of another class

and reuse that code and this class can

also have more specific properties and

methods like a size chart

link one last thing to know is that if

we don't create a Constructor by default

it will run the parents Constructor so

that's why when this class was empty the

code still

worked now that we have this clothing

class we're going to use it in our

project so right now if we scroll down

to our products array we can converted

all of these into a product

class however we're going to convert

some of them like the t-shirt into a

clothing class instead to make it more

specific so how do we know which objects

to convert into a product and which ones

to convert into clothing to help us do

that I included a property called type

so type tells us which class we should

use when we're converting this into a

class this is sometimes called a

discriminator property it tells us which

class we should convert this

to so we're going to go down to the

bottom of this code so I'm going to do a

trick here I'm going to scroll up to the

products array and click this Arrow to

collapse it and then at the bottom we're

going to use that type property to

decide which class to use so inside this

function we're going to use an if

statement bracket ET and curler

brackets and inside we're going to check

the type

property product

details.

type and we'll check if it is equal to

the string

clothing if it is equal to clothing

we're going to convert this object into

a clothing class instead so let's

return new Capital C clothing and

brackets and we're going to give the

Constructor product

details so now our array will contain a

mix of regular products and

clothing next for each of our clothing

we're going to display the size chart

link on the

page but first let's make sure that we

have this image here the closing size

chart so if we go into our images

folder you might see the image here

called clothing siiz

chart.png but currently I don't have

this so I need to download this first to

do that we're going to click this link

in the

description which will open the size

chart

and then on this image we're going to

right click save image

as and then find the folder that

contains all our code so for me it's on

the

desktop inside a JavaScript Amazon

Project and inside the images

folder and we'll save it

here and if we go back to our code we

should have the closing size chart image

inside the images

folder now let's display the size chart

on the

page so if I go to the

homepage whenever we have a clothing

product like this t-shirt we're going to

display a size chart

underneath let's go back to our

code and open amazon. JS which creates

the homepage

which is right

here and we're going to scroll down the

HTML below the product price and the

quantity selector here and underneath

this if we have a clothing product we're

going to display a size chart link under

the quantity selector like

this so one way we can do this is to use

something like an if statement or a

turnery like a this if it's a clothing

then display some HTML if it's not a

clothing then just display

nothing however we're going to learn a

different way to do this using

inheritance so first we're going to

create a new method on the clothing

class that's going to generate the HTML

that we need here so we're going to go

to our code and scroll up and open

products. Js

and we're going to scroll up to the

clothing

class and at the bottom we're going to

create a new method and let's call it

extra

info

HTML brackets and Cur

brackets so this method will generate

some HTML that contains some extra

information about this product like the

size

chart so here we're going to return some

HTML and we use a template string

because we're going to insert some

values inside and inside here let's

create some HTML for a

link to create a link we're going to use

the code less than a greater than less

than SL a greater than so this HTML

element creates a link when we click

this link it will open another page

page inside this link let's put the text

size chart so this is what's going to

show up on the

page and Link elements have two

attributes the first attribute is called

hre Equals double

quotes So this tells the computer which

page this should open when we click this

link inside here we're going to insert

the size chart link so we're going to

insert this. siiz chart

link so when we click this it will open

a page containing the size chart

image we'll scroll back

up and Link elements can have another

attribute called Target equals double

quotes and we're going to give it a

value of underscore blank

and I'll add some new lines here to make

it a little easier to

read so Target equals blank tells the

link to open in a new

tab so now let's save this

file and we'll go back to the homepage

so I'll scroll down here to amazon.

JS and below the quantity

selector let's

insert and we'll call the method that we

just created which is the

product. extra info

HTML and

brackets so this will ins some HTML

containing extra information about the

product like the size

chart now before we run this code

there's one thing that we need to fix

currently only the clothing class has

this

method if it's just a regular product

it's not going to have this method and

it's going to cause an

error to fix this we're also going to

create this method on the product class

so we'll go back to our

code and open products.

JS and we're going to scroll up to the

products class here and at the bottom

we're going to add the same

method extra info HTML brackets and

curly

brackets and for regular products we

don't have any extra info we want to

display so let's just return and empty

string and

save so now if we call extra info HTML

it doesn't matter if it's a product or a

clothing both of these will have this

method

defined so we'll go back to amazon.

JS and now this should always

work so let's click this file and

save and then open the web page to see

the

result so now you notice that products

that are clothing have a size chart

underneath and regular products don't

have any extra

information and if we click the size

chart link it will open a new tab to the

size chart image

so that's how we create this size chart

link for only the clothing

products let's go back to our code and

we'll learn more about this new

technique that we just

used so on the left we'll go back to

products. JS

first so notice that the product class

has a method called extra info HT ML and

then clothing extends this

class that means clothing will

automatically get the extra info HTML

method but then we Define this method

again inside

clothing so this will actually override

or replace the parents method and this

technique is called method

overwriting one more thing to know about

method overwriting is that if we really

need access to the parents method

there's a feature that we can use called

super so super gives us access to the

parent

class so if we want to call this method

up here we can do super and then extra

info

HTML so it's the same super as we used

up here except this calls the parents

Constructor and this calls one of the

parents

methods so let's comment this out since

it's just an

example and let's

save and lastly let's go back to amazon.

JS and we'll take a look at this code

and notice that when we call extra info

HTML we don't know what class this is

this might be a clothing class or a

might just be a product

class this technique is called

polymorphism which means we can use a

method without needing to know exactly

what class this

is polymorphism is sort of like an

alternative to doing if statements here

instead of doing if it's clothing do

this if it's a regular product do

something else we can just have both of

the classes use the same method and then

the class itself will Det determine what

this method

does if we add a new class like an

appliance class we don't need to change

any of this code the appliance class

will determine what extra info HTML

does and that's it we learned about

inheritance which lets us reuse code

between classes and we learn some of the

techniques we can do with inheritance

like method overwriting and polymorph

PRM which can make our code a little bit

cleaner now let's check our test to make

sure that everything still works so

we'll open the test page and make sure

that everything is still passing and

then we'll go back to our code and we'll

save this into git open the git

section and in products.

JS we created the clothing class which

inherits from product

and one thing I forgot to do is to

remove this practice

code so let's actually go back to our

code in products.

JS and below the clothing let's remove

this practice

code and

save we'll go back to

git and just make sure that it's been

removed and then we added the size chart

image

and in amazon. JS we used polymorphism

to add some extra info below each

product so let's create a message

describing our

changes use

inheritance and

polymorphism to add size chart and

commit

in the rest of this lesson we're going

to learn more details about classes the

first detail is how to test classes so

testing classes is the same as writing

normal

tests so we generate an object using a

class and then we test if its properties

and methods are

correct I'll leave writing tests as an

exercise at the end of this

lesson the second detail we're going to

learn is built in

classes these are classes that are

provided by the

language so let's go back to our

code and open products. JS

again and we're going to practice using

a buil-in

class an example of a built-in class is

date this class generates an object that

represents the current date

below the classes that we created we're

going to create some new lines and we're

going to practice using the built-in

date

class first we'll generate a new date

object using the code new and then the

class capital D date and

brackets and now let's save this object

in a variable so at the front we'll use

const and we'll call it date and make it

equal to this object that we just

generated and below this let's

console.log the date to see what it

looks like so we'll

save and then open the

page and we'll go back to our project

here and we're going to check the

console so right click

inspect and the

console and we can see that the date

object represents the current date and

time so this is the current date and

time that I'm recording this

video so this date object has properties

and methods that we can use that are

related to the

date for example we'll go back to our

code and every date object has a method

called two local time string this

basically gives us the current

time so let's try it out we'll create

create a new line and type the code date

dot to local time string and brackets so

make sure that this is in cam case two

is lowercase and every other word starts

with an

uppercase and we'll console.log this to

see what it looks like

console. log and

brackets so let's save this file

and open the

console and that method gave us the time

so for you you should see your current

time

here so that's the built-in date class

it lets us create objects that represent

the current date and

time an interesting thing to know is

that we used the external Library DJs

earlier in the project DJs uses this

date class behind the

scenes however DJs gives us a lot of

extra features so we usually use DJs

instead of using the date class

directly so now let's comment out this

code because it was just an example so

at the top we'll type

slashstar and below it star

slash the last thing we're going to

learn is more detail dets about

this as a

reminder inside an object we can use the

value this and this will point to the

outer

object so this feature lets an object

access its own

properties now in JavaScript this can

actually be used anywhere in our

code for example we're going to create

some new lines

and here we can just directly

console.log

this so here we're using this but we're

using it outside of any object in this

situation there's no object for this to

point to so this will be undefined which

actually makes

sense if we

save and we check our console

this will equal

undefined now originally this actually

equaled the window

object however this Behavior caused

confusion so when they release

JavaScript modules inside a module this

is now undefined which makes more

sense let's go back to our code and

another place we can use this is when

we're creating an object so let's go

down here and we're going to create a

new object using const we'll call it

object two and make it equal to curly

brackets and we're going to give this

object a property let's just call it a

colon give it a value of two comma and

add another property B

colon and we'll set the value of this

property to this Dot

a now you might think that because we're

inside this object this will point to

object 2 however at this point in the

code object 2 has not been created yet

so this doesn't have anything to point

to and this will be

undefined if we

save and then open the

console it will give us an error because

this is

undefined let's go back to our

code so so far if we're inside a method

we can use this and it will point to the

object if we're outside of a method

there's no object to point to and this

will be

undefined and everything makes sense so

far so let's comment this out using SL

star and and at the bottom start

slash now the last important place we

can use this is inside a

function so at the bottom here we're

going to create a

function and let's call it log this

brackets and curly

brackets and inside we're just going to

console. log this

so again we're not inside of any object

so there's nothing for this to point2

and in this situation this will be

undefined as

well below this if we run the function

log this and brackets and

save and check the

console it will tell us that this is

undefined when it's just inside a

regular

function next this actually has a

special

feature so inside a function we can

change this to whatever we want to do

that functions have a method called

call So Below this line let's type the

function name log this and use a method

do call and brackets

so call runs this function so it does

the same thing as the line above except

we can set the value of this to be

whatever we want so the first value that

we give to do call is going to be the

value of this for example we can give it

the string

hello and now this will run the function

and this will be equal to hello if we

save

and open the

console you can see that we set this to

be equal to

hello so that's a special feature of

this inside just a function we can

change this to whatever we want using a

method like

call so call is the same as calling or

running the function except we add an

extra parameter in front this first

parameter is the value of

this the last important thing to know

about this is that Arrow functions do

not change the value of

this for example below this let's create

a method by using an arrow function this

time so we'll create some new lines and

first we're going to create an object

using

const we'll call it object three equals

curly

brackets and inside will give it a

method and colon and we're going to

create this method using an arrow

function this time brackets arrow and

curly brackets and inside we'll just

console. log

this so usually this will point to the

object itself

however Arrow functions do not change

the value of

this here this will have the same value

as outside the arrow

function outside the arrow function

let's type

this here this has no object to point to

so this will be

undefined and then inside the arrow

function it will also be undefined

basically this keeps the value that it

had outside the arrow

function as a test below this we'll run

object 3. method and

brackets if we

save and check the

console it will show us that inside here

this is also undefined

so in an arrow function this will be

whatever the value is outside the arrow

function now you might be wondering why

are Arrow functions designed this

way so JavaScript had a common problem

in the past when we are inside a method

this points to the object but if we try

to do a for each Loop inside the for

each Loop this does not point to the

object anymore it points to undefined

and that's because we created a whole

new function here and remember inside a

regular function this becomes

undefined so this caused problems

because we no longer had access to the

outer object up

here so that's why we created Arrow

functions if we replace this with an

arrow function this would be equal to

whatever it is outside the Arrow

function Arrow functions do not change

the value of

this so outside for each this points to

the object and inside for each this also

points to the

object so that's why Arrow functions are

designed this way to avoid accidentally

overwriting

this so let's summarize what we learned

about this inside a method this points

to to the outer object inside a function

this is undefined but we can change it

to whatever we want using something like

call and arrow functions do not change

the value of

this don't worry if these rules are a

bit confusing at first they are actually

sort of

reasonable if there's an object to point

to this will point to that object if

there's no object to point to this will

be undefined and we have tools like call

and arrow functions to kind of

manipulate the value of this to be what

we want the more that you work with it

the more you just get used to

it so now let's comment out this

practice code at the top we'll type

slashstar and at the bottom star slash

and

save and we'll save to get

we'll open the git

section inside products. JS we added

some practice code to learn more details

about classes and

this let's type a message describing our

changes learn more details about classes

and this and commit

now that we learned object-oriented

programming you might notice that it's a

very different style of programming than

just writing out a bunch of functions

directly so you might be wondering which

style of programming should we use

objectoriented programming or procedural

programming which is the step-by-step

style that we used in the earlier

lessons the answer is it's up to you I

personally prefer procedural programming

in JavaScript because I think it's

simpler I only use objectoriented

programming if I'm working on a team

that also uses it also object-oriented

programming is much more popular in

other languages so it's still useful to

know object-oriented programming in case

you work with other programming

languages in the

future and that's the end of this lesson

in this lesson we learned about

objectoriented programming which means

we organize our code into objects we

learned how to use a function to

generate objects and we improve that by

using a class to generate objects we

learned that classes can have private

properties and methods we learned about

inheritance which lets us reuse code

between classes and we learned about

method overwriting and polymorphism

which lets us call a method without

needing to know what the class is and

lastly we learned more details about

this and how to control the value of

this thanks for watching this course so

far if you want to support this channel

you can check out the premium version of

my courses just like this one where you

can get a certificate of completion and

a Better Learning platform if you're

interested in extra videos from me more

in-depth videos and behind the scenes

content you can check out these links

here you can also support the channel by

liking the video subscribing and sharing

this video with others thanks again and

let's continue with the

course here are some exercises to help

you practice what we learned in this

lesson

in this lesson we're going to learn

about backend and this will prepare you

for the next step after finishing this

course first of all

what is backend a backend is just

another computer that manages the data

of a

website for example in our Amazon

Project we created this website where we

can pick which products we want but how

does Amazon the company know which

products that we

ordered in this situation there has to

be a second computer somewhere that's

owned by

Amazon and then our computer sends the

order information to this second

computer and now Amazon will know what

we

ordered so this second computer is

called the backend computer or just the

backend it manages the data of a

website on the other hand our computer

or the web page where we can see and

interact with the products this is

called the front end

now that we know what a backend is how

does our computer or the front end send

information to the back end when two

computers are connected to the internet

they can actually send messages to each

other using a feature called

HTTP or hypertext transfer

protocol in an HTTP message we can

actually attach information like our

Amazon order

when Amazon's backend receives this HTTP

message now Amazon will know what we

ordered now that we know what HTTP is

let's send our first HTTP message using

JavaScript so we'll go to our code and

on the left we're going to create a new

file just for practicing backend so

we'll scroll up to the data folder and

we'll click inside this folder and then

create a new

file and let's name this file backend

Das

practice. JS and press

enter and now to send an HTTP message

we're going to use a class called XML

HTTP request so this is a built in class

meaning it's provided by

JavaScript first we gener at an object

using this class using the code

new and the class name

XML all capital capital

HTTP capital r request and

brackets so this creates a new HTTP

message that we want to send to the

backend a message is also known as a

request so now let's save this request

in a variable at the front we'll create

a variable with const and name it

xhr equals this

request next we need to set up this

request so we'll create a new line and

to set it up we'll do xhr

doop and

brackets and to set up this request

we're going to give open two

parameters the first parameter is what

type of HTTP message to

send so one type of message we can send

is the string

get get means we want to get some

information from the back

end there are several common types of

requests that we can give to the backend

but we're going to start by learning get

next we're going to give open a second

parameter and this parameter tells a

computer where to send this HTTP message

so using HTTP we can send a message to

any computer that's connected to the

internet now to locate another computer

on the internet we need to use a

url url stands for uniform resource

locator and it's kind of like an address

but for the internet a URL helps us

locate another computer on the

internet so URLs look like this this is

the URL for Amazon YouTube and my

website the https in front means we're

using HTTP to communicate with this

computer the S after the http means

we're using a secure version of http

the second part of a URL is called a

domain name this is like an address it

points to another computer on the

internet so amazon.com points to one of

Amazon's backend computers youtube.com

points to one of YouTube's backend

computers and superimple dodev points to

one of my backend

computers if you want to learn more

about domain names and how the internet

works you can check out my video on how

to put a website on the

internet now for this lesson I actually

set up a backend computer that we can

practice with so my backend is located

at the URL

https super simple backend

dodev so in the second parameter of open

we're going to give it a

string and we're going to give it the

URL of the back end end that we want to

send the message

to so the URL for my backend is

https colon SL SL super simple

backend.

death so that's how we set up an HTTP

message we give it the type of message

we want to send and also the URL which

is where to send this message to

the last step is to just send this

message so we'll create a new line and

we'll type xhr

doent brackets and

save so this creates a new HTTP message

sets it up and then sends this message

across the internet to my backend

computer located at superimple backend.

deev so now let's actually run this code

and see the results we're going to go to

the left and we're going to open

checkout.

JS and in here just like we did before

we're going to load that practice file

that we just created so we'll create a

new line and we're going to import a

file or a string and we'll locate that

practice

file so first we need to go to the data

folder using using do dot SL dat slash

and load

backend D

practice. JS and

save so we'll go back to the practice

file and now when we open the website it

will run this code and send the HTTP

message to see that let's open the

website so we'll scroll down and if you

don't have the website open you can open

it again by right clicking checkout.

HTML and then open with live

server I already have the website open

so I'm going to open

it and then I'm going to go to the

checkout

page and now we're going to look at the

console so we'll right

click and

inspect and this time instead of going

to the console tab we're going to go to

a new tab

called the network

tab if you don't see this tab you can

make this window wider or you might find

it under these

arrows so we'll open the network

Tab and in here this will show us all

the HTTP messages that are coming in and

out of our

computer now before we start looking at

the the HTTP messages there's one

important thing to know about the

network Tab and that is messages will

only appear here after we open the

console if we send some messages and

then we open the console it's not going

to show up

here so to make sure our HTTP messages

are recorded here we need to open the

network tab first and then we're going

to refresh the page to resend those

messages and now if we open the network

tab we should be able to see the HTTP

messages at the

bottom okay so inside this list we

should be able to see that we sent a

message to superimple backend. deev if

you don't see it we can also search this

list by using the text box up

here so in here we can type part of the

URL that we sent the message to for

example super

simple and the message that we sent

should appear here so now we can click

this message to get more details about

it on the right side we have several

tabs here the headers tab gives us

details about our message or about our

request so it tells us which type of

requests that we sent which is get and

the URL that we sent it to which is

super simple backend.

Dev this sends the request across the

internet to my

backend and then when my backend

receives this message or this request it

will send back a message which is called

a

response to see the response from my

backend we can open the the response

Tab and you can see that my backend

responded with hello this is super

simple dev's back end and a

documentation page that we can check

out so we have successfully sent an HTTP

message or a request to my backend and

we got back a

response another useful tab here is the

preview tab it basically takes a

response and displays it in an easy to

read

format so now let's learn some

terminology when we send a message to

the backend this message is called a

request we are requesting something from

the

backend when the backend receives our

request it will send an HTTP message

back to us and this message is called

the

response so each request that we make

will get one response from the back

end and this is called a request

response cycle it's always one request

one

response next currently we're viewing

the response in the network tab but we

can actually get this response in our

code and then do something with this

response so let's go back to our

code and here after we send the requ

Quest we can get the response using a

property called xhr do

response however there's a slight

problem with doing this when we send a

request to the backend it takes time for

the request to travel across the

internet to the back end and for the

response to come

back so the response is not available

right away and xr. response will be

undefined at first so xr. send is known

as asynchronous code asynchronous code

means it does not wait for this line of

code to finish it just sends the request

and then immediately goes to the next

line the response might come back later

in the future but we don't have access

to it

here so in this situation in order to

get this response we need to wait for

the response to come back first and then

we can access do

response in order to wait for the

response to come back at the top after

we create the

xhr we're going to use this code

xhr do add capital E Event capital L

listener and

brackets so this method listens or waits

for an event and then it can run a

function so this method takes two

parameters the first parameter is the

event that we want to listen for or to

wait for in this case we want to wait

for the response to come back so we're

going to give it the string load load

means the response has

loaded the second parameter is a

function that we want to run

after this event

happens so in this case after the

response has loaded we're going to run a

function brackets arrow and curly

brackets so because this function runs

after the response loaded inside here we

can access xhr do

response and this will not be undefined

it will contain the response that we saw

earlier in the network

tab so let's console.log this to see

what it looks like

console.log and

brackets and we'll remove this line at

the

end and

save so now let's go back and check the

console for the response so we'll open

the

console and then open the console

Tab and here you can see that we have

the response in our code and we console.

logged

it so this

response is a string and now we can save

this in a variable or do whatever we

want with it in our

code now one thing you might be

wondering is why do we put the event

listener up here at the top so first we

need to set up the event listener and

then trigger the event or send the

request this is the same as setting up

an event listener for clicking a button

we need to set up the event listener

first and then we click the button

after so that's how we send a request to

the back end wait for the response and

then save the response in our

code next we can send different messages

or different requests to the backend

using URL

paths a URL path is the part that comes

after the domain name for example in

this URL the URL path is /hello in this

URL the URL path is/ products

slir in this URL if there is no URL path

the URL path is

slash we can send a request to these URL

paths and each URL path will give us a

different

response so let's try sending requests

to different URL paths and see what

different responses that we

get so for this example let's send the

request to super simple backend. deev

and then the URL path SL hello and

save and now let's open our console to

see the response

and here you can see that this URL path

gave us a different response than last

time let's go back and try another URL

path to see what it looks like so we'll

delete this and then send the request to

slash products

slir and

save and we'll open the console to view

the

response and here here this URL path

give us a Json and this contains the

details of the first product in our

Amazon

Project so we can send requests to

different URL paths and we will get

different responses from the

backend next a backend only supports a

certain set of URL paths for example

when I created my backend super simple

backend .d I had to decide which URL

paths are supported and how my backend

would respond to each URL path if we

send a request to a URL path that is not

supported the back end will respond with

an

error let's go back to our

code and we'll try a URL path that is

not

supported so let's remove this at the

end

and we'll try sending the request to

not-

supported and

save and now if we look at our

console you'll see that the backend

responded with an error message saying

this URL path is not

supported the browser will also

console.log this red error

message this red message is displayed

automatically when there's an error

so this message tells us the type of

request that we sent which is get and

the URL that we sent it to and also this

number which is called the status

code whenever we get a response from the

backend the backend also gives us a

status code which tells us if a request

succeeded or

failed a status code that starts with

four or five means the response

failed starting with four means it was

our problem we sent the request to a URL

path that was not

supported starting with five means it

was the backends problem for example the

backend

crashed a status code starting with a

two means the response was

successful so we can also see the status

code in the network

tab so we can search for our request and

then when we click the request in the

headers tab it will show us the status

code in this

row so this tells us if our request

succeeded or

failed so now you might be wondering how

do we know which URL paths are supported

and which are

not so there's actually no way to figure

out all the URL paths that are supported

and this is for security reasons

however some backends do provide a

documentation page that lists the URL

paths that are supported and also what

kind of response that they give for my

backend I created a documentation page

and we're going to take a look at that

so we'll open the

browser and at the top we're going to

create a new

tab and to see the documentation for my

backend we're going to go to super

simple back back end dodev SL

documentation and press

enter so this is the documentation page

for my backend it gives us a list of

which URL paths that are supported and

what each URL path does so when we make

a request to slash it will give us this

message which we saw earlier if we make

a request to/ hello it will give us this

message which we also saw

earlier so by the way the list of all

the URL paths that are supported is

called the backend

API API means application programming

interface interface means how we

interact with something so this list of

URL paths are all the ways that we can

interact with the backend and that's why

we call this the backend

API next the backend can respond with

different types of data so one type of

data the back end can respond with is

text for example when we sent the

request to get/ hello it gave us some

text

back so in our

code if we change this URL path to

/hello

and

save and we open the

console and click the console

tab it gives us back some

text we can also see what type of

response that we got using the network

tab so we'll open the network Tab and

then search for the

request and then here when we click

it inside the headers tab if we scroll

down to the response

section here it will give us the content

type or the type of response that we got

back so in this example /hello gave us

some text and the type is text

slpl another type of data the backend

can respond with is

Json so if we go back to our code and

change the url path to products

slir and

save and then look at our

console in the network tab we'll open

this request and inside the headers if

we scroll

down it will tell us that the type of

the response is application SL

Json so the backend sent us back some

Json if we open the console tab we can

see the Json string here

so once we get this Json from the

backend we can use json.parse to convert

this back into a JavaScript

object basically this allows us to send

JavaScript objects across the internet

to the back

end another type of data the back end

can respond with is

HTML we'll go back to our

code and we'll change the URL path to

documentation so this was the

documentation page that we saw earlier

if we

save and then open the

console you'll see that the back end

responded with a bunch of

HTML if we look at the network Tab and

search for the request and open the

request here and in the headers tab we

scroll down

to the content type it will tell us that

the type of the response was text/html

finally another type of data the backend

can respond with is an

image for example we'll go back to our

code and change the url path to

imagesapple

jpg and say

save and we'll open the

console and in the network tab we can

open this

request and in the headers tab we can

scroll down and it will tell us that the

type of response was an

image/jpeg as you can see the backend

can respond with different types of data

not just

text okay so we got this image back from

the back end but what does this look

like in the console we'll open the

console and we'll see that we just get a

bunch of random characters here and

that's because the console is trying to

display the image as text but the image

is not really

text this is the image's raw data so

that's why it shows all these random

characters

here however it would be better to

display this as an actual ual image

instead of raw

data we can display this as an image by

using the

browser so if we open the

browser when we type a URL at the top of

the browser it actually sends a get

request to that

URL so typing in here actually does the

same thing as our code it makes a get

request the one big difference is that

that in the browser when it gets back

the response it will display the

response on the

page for example if we enter superimple

backend dodev and change the url path to

just nothing or slash and press

enter this actually sends a get request

to my back end the backend responds with

some text and it displays this response

on the

page so using the browser is the same

thing as making a get

request now the cool thing about this is

that if the browser gets back an image

it will display it as an actual image

instead of raw data that we saw in the

console so here if we change the url

path

to/ images

slapple jpg and press enter

it will get back the same image as

before except the browser will display

it as an actual image on the

page same thing happens with the backend

responds with

HTML so at the Top If we change the url

path to slash

documentation and press

enter if the response from the back end

is HTML theow browser will display this

HTML as an actual web page instead of

raw

HTML so again using the browser is the

same thing as making a get

request and depending on the type of

response the browser can display the

response in a more useful way on the

page and that's it we learn the basics

of how a backend Works how to send

requests to a backend and how to send

requests to different different URL

paths so now let's go back into our

code and we'll remove this URL path and

just dodev so that we don't keep console

logging and image and then

save and let's save this practice code

into git we'll open the kit

section in backend practice we learn how

to make requests to the backend and in

checkout. as we loaded that backend

practice

file so let's type a message describing

our

changes add backend

practice file and

commit now that we learned what a

backend is and how to communicate with a

backend let's use a backend in our

project

so first we're going to open our code

and we're actually going to open

checkout.

JS and we're going to comment out this

import statement because we're not going

to run the practice file anymore so

we'll type double slash to comment that

out and

save next super simple backend dodev has

a URL path called slash

products this gives us a list of all the

products in the Amazon Project so first

let's open our browser and visit this

URL path to see what the response looks

like we'll open this tab to super simple

backend dodev and we're going to change

the url path at the end to slash

products and press

enter and you can see that this URL path

gives us a Json response so this

contains all the details of the products

for our

project now instead of using a file on

our computer to load the products let's

use the backend to load the

products so let's go back into our

code and on the left we're going to open

data/ products.

JS and we're going to scroll down to the

array of prodct S at the end so now

instead of loading the products from

this file we're going to load the

products from the back end so first

let's comment out all this code if you

need to you can click this arrow on the

left to collapse this array and we're

going to comment this out using slash

star and at the end star

slash and above this we're going to load

the products from the back end

first let's create a variable to save

the products again so we use let

products equal and empty array and let's

export this so we can use it outside of

this file like before at the front we'll

type

export next let's create a function to

load these products from the back end

we'll create a

function and let's name it load products

brackets and curly

brackets and inside here we're going to

create an XML HTTP request again to make

a request to my

backend so to create a request we're

going to use new in the class XML HTTP

request and brackets so this will

generate a new request object and let's

save this in a variable

so at the front we'll use const and

we'll name it xhr equals this

object next we're going to set up the

request using xhr doop and

brackets so open takes two parameters

the first parameter is the type of

request that we want to send in this

case the type of request will be the

string get

and we're going to give open a second

parameter which is the URL that we want

to send this request to so we'll give it

a string and the URL of my backend is

https colon slash super simple backend

dodev and then we'll add the URL path

which is slash

products finally we're going to send

this request using the code xr. send and

brackets so this will create and set up

a request and then send it to my backend

now remember that do send is

asynchronous that means it will just

send the request but it will not wait

for a response to come

back in order to wait for a response

above this code we're going to create

some new lines and set up an event

listener using

xr. add event listener and

brackets and this takes two parameters

the first one is the event we want to

listen for in this case it's the string

load which means the response has

loaded next we're going to give it a

second parameter which is a function so

brackets Arrow and curly

brackets and this is a function that we

want to run after the response has

loaded so inside here after the response

has loaded we can access it using xhr do

response for now let's console.log this

to see what it looks like so we console.

log and brackets

finally let's run this function so that

we run all this code at the bottom we're

going to load products and

brackets and

save so this will send a request to my

backend and then once we get the

response it will display it in the

console so now let's go to our

website we're going to open the project

tab

and don't worry if the page is blank for

you we're going to fix this in a bit for

now we're going to open the console by

right

clicking

inspect and open the

console and in here you'll see that xr.

response gave us this Json and this

represents all the products in our

Amazon

Project now that we have all this Json

we're going to convert this back into a

JavaScript object and then use it in the

rest of our code let's go back to our

code and here the response is a

Json we're going to convert it back into

a JavaScript object or in this case a

JavaScript array using the code

json. pars and

brackets so once we' converted this back

to an array we're going to replace the

product up here with what we loaded from

the back end to do that we'll do

products and make it equal to this

result that we got from the back

end now one more thing we need to do is

previously we converted the product

objects into a class so we're just going

to do that again with this

array so we'll select the code from map

all the way to the end

and then right click

copy and

here after this products array that we

got from the back

end right click

paste we're also going to transform this

array from objects into these

classes and at the end let's console.log

this products array to see what it looks

like now so we'll console

. log

products and

save and now if we open the console for

our

project you'll see that products is now

an array of product classes and clothing

classes so we converted the response

from a Json into a JavaScript array and

then into these

classes so that's how we load data from

the the back end and then convert it

into a JavaScript object or array that

we can use in our

code next let's go back to our code and

instead of console. loging the products

every time which will display a lot of

stuff in the console let's just

console.log a message to make sure that

this is working so we'll change this to

the string load products

and now that we have this function let's

use it in each of our

Pages first we're going to remove

calling this function for now and we're

going to export this function so we can

use it outside of this file so

export and save this

file and we're going to start from the

homepage so we'll scroll down to the

bottom to amazon.

JS and we're going to scroll to the

top and first we're going to import load

products we're already importing from

products. JS so we'll just add a comma

and load

products and now before we run all of

this code at the top we're going to load

the products first and brackets

so now let's

save and open the project in our

browser and we'll click the top left

icon to go to the

homepage and you'll see that the

homepage is actually empty so what went

wrong

here remember that HTTP requests are

asynchronous if we go back into our

code load products will send a request

to my backend

but it takes time for the request to

travel across the internet to my backend

and to travel

back so here it will just send the

request and at the next line the

response has not loaded yet so the

products array is still

empty and when we run this code with an

empty array the page will be

empty to solve this problem we need to

wait for this HTTP request to finish

first and for the response to come back

and then we're going to run the rest of

this

code so how do we do

that so we're going to go to the left

and we're going to scroll up to data/

products.

JS and I'm going to drag this file to

the top so we can see the code side by

side and I'll scroll down to the HTTP

request

which is right

here and remember that we used an event

listener to wait for the response to

come back once the response is loaded

we're going to run this

function so basically we want to run all

of this code at the bottom of this event

listener so after we've loaded our

products so one way to solve this

problem is maybe we can just copy all

this code and then paste it at the

bottom

here now obviously this doesn't make

sense because we're copy pasting a bunch

of code and then we can't really reuse

this

function a better solution is we're

going to put all this code in a

function and then we can give this

function to load products let's do this

step by step

so first at the top let's create a

function to group all of this code

together we'll use the word

function and let's name it render

products grid brackets and curly

brackets and now we're going to move all

of this code into the

function so we can do that by removing

this closing curly

bracket and then at the bottom we we're

going to scroll down all the way to the

bottom here we're going to add back the

closing curler bracket to put all this

code inside the function and now let's

also select this code so we can fix the

index so we'll select it all the way up

to

here and then press tab to add an indet

so now we put all the code inside render

products grid

next we're going to put this function

inside load products using a parameter

so between these brackets we're going to

give it this

function

render products

grid so remember in JavaScript functions

are values and we can use a function as

a

parameter so now inside load products if

we go up here at the top this function

will be saved in a parameter so let's

create a parameter at the top and we'll

name it fun to say that this parameter

will contain a

function so we basically saved this

function inside this parameter and now

after we load the response we're going

to run the

function so at the bottom here after

we've created the products array we're

going to run font and

brackets so that's how we run all of

this code after we've loaded the

products we group this code into a

function and then we save the function

up here after we load the response we're

going to run the

function so let's save these two files

we'll save products. Js

and then down here we'll save amazon.

JS and then open our

website and you'll see that the products

loaded again because this time we're

waiting for the response to come back

and then we run our

code so that's how we wait for an HTTP

request to finish first and then we run

some

code by the the way this function that

we provide to load products this is

known as a call back because we're

giving it a function to run in the

future or to call in the future so this

function will be called back in the

future and we've actually used call

backs before when we wrote the code set

timeout we provided set timeout a

function to run in the future or or to

call in the future so this function is

also known as a call

back don't worry if this technique is a

little complicated at first the more you

work with callbacks the more you'll get

used to

it let's get some more practice and use

the backend and callbacks on the

checkout page so we're going to open

checkout. JS which is the checkout page

and first we're going to in import load

products so at the top we'll create an

import curly brackets load

products from a

string and we'll locate products. JS so

inside here we're in the scripts folder

we're going to get out of it using do do

slash and then we're going to go into

the data

folder and then we'll add slash data

slash and we'll load products.

JS and then down here we're also going

to load products and

brackets and again we're going to give

load products a call back or a function

that we want to run in the

future this time instead of creating a

whole new function we're just going to

create a function in inside these

brackets using brackets arrow and curly

brackets so we don't need to create a

function name every time we can also

just create an anonymous function or a

function without a

name and then give this to load products

to run in the

future now inside this Anonymous

function we're just going to move this

code into here so we'll select this code

and then rightclick

cut and then inside here we're going to

rightclick and

paste and if you need to you can fix the

formatting so again this is going to

save this function inside the parameter

fun and then we're going to call fun

after we've loaded all the

products so let's save this file

and open our

website and we'll click the cart in the

top right to go to the checkout page and

now the checkout page is loading

again so that's how we use a backend in

our project we need to send a request

and then use a call back to wait for a

response and then run the rest of our

code so now let's save our changes into

G

we'll go to the git

section and in products.

JS we created the load products

function in amazon.

JS we used load products and gave it a

call

back and in checkout. JS we also used

load products and we gave it a call back

using an anonymous function or a

function without a

name let's create a message describing

our

changes load products from the backend

and

commit next we're going to learn testing

with a

backend now that we're using a back back

end in our code we need to update our

tests first let's go to our code and

we're going to run our tests so we'll

scroll to the bottom and if you don't

have the tests open we can run them by

right clicking test.html and then click

open with live server now I already have

the test open in my browser so I'm just

going to open that

Tab and for the video I'll zoom in using

control equals or command

equals and we have some failing tests

now so if you did the exercises from the

previous few lessons you might have more

than two failing tests but we're going

to focus on fixing these two tests here

for the

video so first let's open the code for

our order summary tests we'll open vs

code and then on the left we're going to

go into the test folder SL checkout SL

Ord summary

test.js so now we're going to scroll

down in this test and notice that here

we are rendering the order summary which

creates the cart on the checkout

page however this card requires the

products to be loaded from the back end

and currently we're not loading the

products in our tests so that's why the

tests are failing we need to to load the

products

first to do that let's import the load

products function at the top so we'll

scroll

up and we're going to add another

import curly brackets the load products

function from a string and we'll locate

products. JS so we need to get out of

checkout and out of tests using do do

slash do do slash and and then we'll go

into the data folder data/ and load

products.

JS and now we could call load products

inside before each but this will load

the products before each of our tests so

it will load it multiple times and we

don't really need to do this we only

need to load the products once for all

of our

tests to do that we're going to use

another hook provided by Jasmine called

before

all so above before

each we're going to use the function

before all and

brackets so this is the before all hook

it will run a function before all of our

tests inside these brackets we're going

to give it a function to run so brackets

arrow and curly brackets

and now before all of our tests we're

going to load the products so let's load

products and

brackets and

save and now let's open our tests in the

browser and unfortunately the tests are

still

failing let's go back to our code and

see what the problem is we'll open vs

code and here

remember that load products is

asynchronous that means it just sends a

request to my back end but it doesn't

wait for the response to come back so it

would just send a request and then

continue with the rest of the test

code and unfortunately at this point the

response has not come back yet products

is still an empty

array to fix this issue we need to wait

for a load products to finish first and

then continue with the rest of the

test to do that Jasmine has a feature

for waiting for some code to finish

called a done

function so in before all we can give

this inner Function One parameter called

done so done is a function and it's

provided by Jasmine when we we add this

done parameter before all will not

automatically go to the next step now

it's just going to wait and it will only

go to the next step when we call this

done function so when we do done and

brackets then it will go to the next

step if we don't call done then before

all we'll just keep waiting forever so

this done function allows us to control

exactly when before all finishes and

goes to the next

step and this is what we need to fix the

test we need to wait for load products

to finish first and then we're going to

call done and then go to the next

step to wait for load products to finish

remember we're going to give it a

function so between these brackets we'll

create a function using brackets Arrow

and curly

brackets now once the products have

finished loading it will run the

function inside here we're going to call

done and

brackets so this makes sure that the

products load first and then we call

done and then it goes to the next step

which is the before each hook and then

eventually it runs the tests at the

bottom

so now let's

save and take a look at our test page

and you'll see that those order summary

tests are now passing if you have any

other fail tests I'll leave that as an

exercise let's go back to our

code and that's how we test with a

backend we wait until the backend code

is finished and then we use the done

function to control exactly when to go

to the next step by the way we can also

use done inside before each and inside

it as well to wait for backend code to

finish now let's save our changes into

git we'll open the get section and

inside order summary test we imported

load products and then we called load

products and use the done function to

make sure that the products are loaded

first and then we go to The Next

Step let's create a message describing

our

changes load products in before all hook

and

commit next we're going to learn

promises which are a better way to

handle asynchronous code promises are

similar to Jasmine done function that we

just learned they let us wait for some

asynchronous code to finish before going

to the next

step so now let's create our first

promise we're going to open our code and

on the left we're going to go to

checkout.

JS and in here at the top we're going to

practice promises

promise is a class so we're going to

type the code new capital P promise and

brackets to create a new promise

object now inside these brackets we're

going to give it a function so brackets

arrow and curly

brackets so that's just how promises are

designed it's a built-in class and when

we create a promise we need to give it a

function

so when we create This Promise it's

going to run this function

immediately so inside here let's

console.log the string

promise to show that it runs

immediately so we'll save this

file and then go to the

website and we'll open the tab for our

project

and I'm going to zoom out a bit by

pressing control or command

minus and then open the console right

click

inspect and the

console and you'll see a logged

promise so when we create a promise it

runs this inner function

immediately now this inner function gets

a parameter called called

resolve and resolve is a function and it

works very similar to Jasmine's done

function so resolve lets us control when

to go to the next

step for example let's add some

asynchronous code into this

promise we'll remove the

console.log and we're going to run load

products which is asynchronous

so here we'll type load products and

brackets and now we're going to give

load products a callback function like

we did down

here brackets arrow and curly

brackets so it will run this function

after load products is

finished once this is finished we want

to go to the next step so here we're

going to call resolve so resolve and

brackets so you can see that the syntax

here is very similar to jasmin's done

function we run some asynchronous code

and then we wait for it to finish and

then we call resolve to go to the next

step now what is the next step to This

Promise so you might think that this

code down here is the next

step however a promise actually creates

a separate line of code or a separate

thread of

code so here these two groups of code

are sort of running at the same time

feel free to pause the video to get a

longer look at this

diagram the reason promises are designed

this way is it allows JavaScript to do

multiple things at the same

time so when the promise finishes it can

do a Next Step but this next step is

going to be separate from the rest of

the code it sort of does the next step

on the

side so right now this promise creates a

separate thread of code but this

separate thread doesn't actually have a

next step so we're going to add

one to add a next step to a promise at

the end and we're going to use a method

called dot then and

brackets and we need to give then a

function so we're going to type brackets

arrow and Cur

brackets and inside here let's just

console.log the string Next

Step so first we run this asynchronous

code and then we wait for it to finish

and then we run resolve and resolve

makes it go to the next

step to make this easier to see in the

console let's actually add some console.

logs to track the progress of this code

so at the top let's

console.log the string start

promise and then in here let's

console.log the string

finished

loading and we'll also comment out the

code that we had

before so we'll type

slashstar and at the bottom star slash

and now let's

save and check our

console so let's go through this step by

step first we start the promise which we

see here

and then we call load products which we

see here once the products are finished

loading it's going to run this function

and then we'll display finish loading

and then we're going to call resolve

which goes to the next step which runs

this function and we display Next

Step so resolve lets us control when to

go to the next

step in this case we waited until load

product prods was finished and then we

called resolve to go to the next

step so that's how promises work they

let us split our code into separate

steps and then we can wait for one step

to finish before going to the next

step now that we understand promises

let's convert the code that we had

before from a call back to using a

promise so first let's remove these

console. logs to make our code a little

easier to

read now in our previous code we

actually had two steps the first step is

to call load products and then once this

is finished the second step is to call

render order summary and render payment

summary and in our promise we have the

same thing our first step is load

product

once this is finished we're going to

call resolve and then go to the Second

Step so we're just going to copy this

second step into the second step up here

so we'll select this code and then right

click

copy and in do then we're going to right

click and

paste and now let's save

and let's check the web page so we'll

open the project and you can see that

everything is loading

correctly So This Promise does the same

thing as a call back that we had before

both of them have two steps the first

step is to load the products and then we

wait for the products to finish loading

and then we do the Second Step which is

to render the page

so now you might be wondering why do we

use promises it looks like it's more

work and more code than just using a

callback so callbacks have a big problem

which is multiple callbacks cause a lot

of

nesting nesting means having code inside

code like

this to see why this is a problem let's

say that we want to load the cart from

the back end as well I actually set up a

URL path that we can use to practice

called SLC

cart so first let's go into products.

JS and we're going to copy load products

and change it to load the

cart so we'll select this

function and then

rightclick

copy and let's open cart. Js

since we're going to load the cart from

the back end and let's scroll down to

the

bottom and here we'll right click and

paste that

code and now instead of loading the

products let's load the cart from the

backend so first let's rename this

function to load Capital C cart

and the first thing we need to change is

the URL path so instead of loading SL

products we're going to load slash cart

from my

backend so normally when we load SL cart

the backend will give us a cart

array however since we're just

practicing my backend will just give us

some text when we load SL

cart next we don't need this products

code anymore so we can select it and

then delete

it and instead let's just console. log

brackets and we just display the

response that we get back xhr do

response and we can remove this other

console.log and

save so now let's use load cart in our

previous

example on the left we'll scroll down

and open checkout.

JS and at the top let's import load cart

so here we'll import curly brackets load

cart from a string and we'll go to the

data folder which is do

dotdata slash and we'll load C.J

and now we're going to use this in our

callback code to show the problem with

callbacks first let's comment out this

promise so we can focus on the Callback

code at the top we'll type

slashstar and here star

slash and we'll remove the comments for

the

Callback and after we load the products

we're also going to load the

cart so inside this function we're going

to type load cart brackets and we're

going to give it a

function so this function is going to

run after the cart has

loaded so now let's say that we want to

wait for the products and the cart to

load before we render the

page to do that we need to move this

code inside this inner

function so we'll select this and then

right click

cut inside load cart we're going to

right click and

paste and remove this extra

line so now this code is going to load

the products wait for it to finish and

then it's going to load the cart and

then wait for the cart to finish

and then it will render the page or

display the page so let's

save and check the

console and now you can see that we

loaded the products and then we loaded

the cart and if we open the

page everything was displayed

properly so now let's go back to our

code and notice that when we added

another call back we we created another

layer of

nesting so we have code inside code

inside

code the problem with this is that each

layer of nesting adds some indents at

the front or spaces at the

front this means if we have lots of

callbacks our code will become more and

more nested like

this this is a big problem with

callbacks multi multiple callbacks cause

a lot of nesting and all these indents

make our code hard to work

with the promises solve this problem by

letting us flatten our

code for example let's load the products

and the carts again but this time using

our promise

instead first let's comment out the

Callback using

slashstar and and at the bottom star

slash and we're going to uncomment the

promise so here we'll remove the

comments and then in the next

step instead of rendering the

page we're going to load the cart like

we did down here so we'll type load cart

and

brackets now we have a problem here we

want to wait for load card to finish and

then go to the next step however we

usually do this using resolve but we

don't have resolve inside this

function to solve this problem inside.

then we can actually return a new

promise so at the top we're going to

return a new promise and

brackets so we're going to give this

promise a function just like we did up

here so we'll type brackets arrow and

curly

brackets and this function gets one

parameter called

resolve so inside do then if we want to

use resolve to wait for some code to

finish we can return a new promise

so now let's move our code into this new

promise so we can use resolve so we'll

select this code and then right click

cut and inside here we're going to right

click and

paste and remove these new

lines and we can give load card a

function to run when it's finished so

we'll type brackets arrow and and curler

brackets once load card is finished it

runs this function and then inside here

we're going to call resolve so that we

move to the next step so here we'll call

resolve and

brackets so now this will go to the next

step and we currently don't have a next

step to This Promise so let's add The

Next Step at the end to add another step

we're going to use dot then

brackets and we'll give this a function

brackets arrow and curler

brackets so the third step is to render

the page so we're going to do the same

thing inside

here so let's select this code and we'll

rightclick copy

inside the third step we're going to

right click and

paste and adjust the formatting if you

need

to so that's how we do these three steps

in the Callback using a

promise we do the first step wait for it

to finish call resolve and then it goes

to the second step we do the Second Step

wait for it to finish call resolve and

and then we go to the third

step so we promise let us have as many

steps as we want and we can use resolve

to wait for each step to finish before

going to the next

step so let's save this and check the

console to make sure it worked so we'll

open the

console and inside here we have the same

messages as last time first we load the

products we wait for it to finish and

then go to the next step then we load

the

cart wait for it to finish and then go

to the next step and then we render or

display the page if we open the page

you'll see that everything displayed

properly so now let's go back and

compare promises and

callbacks so even though promises

require a bunch of setup code you can

see that it keeps our code relatively

flat the third step doesn't get more and

more nested like in

callbacks so if we have lots of steps in

our promise this is what the code will

look like you can see that even when we

add more steps the code does not become

more and more

nested so promises help keep our code

flat

and avoid too much

nesting so that's why it's recommended

to use promises instead of callbacks

promises will keep our code more

flat so let's actually add some new

lines here as well as

here to better separate these steps so

it's a little easier to read

lastly we're going to learn two more

features of

promises the first feature is we can

give resolve a value so inside here

let's give it a value like the string

value

one so whatever we give to resolve is

going to be saved in a parameter inside

doth so inside this function we can add

a parameter called value

and now whatever we give to resolve is

going to be saved inside here and now we

can use

it so this lets us share a value between

two steps of a

promise so in here let's check if this

worked using

console.log

value and

save and if we look inside our

console you'll see that it displayed

value

one so whatever we give to resolve will

be saved in this

parameter the second feature is we can

run multiple Promises at the same time

currently we wait for things to load one

at a time for example we wait for the

products to load and then we wait for

the cart to load and then we go to the

next step to make this more efficient we

can actually load the products and the

cart at the same

time to do that we can use a feature

called

promise.all promise.all lets us run

multiple Promises at the same time and

wait for all of them to

finish so let's scroll to the top and

we'll do an

example so here we'll type the code

capital P

promise.all and

brackets inside these brackets we're

going to give this an

array inside this array we can give it

multiple promises to wait

for so let's just copy paste the two

promises that we have here into this

array so we'll start from here at the

end of the first promise and we'll

select this code right click

copy and in this array we're going to

right click and

paste and remove this line so we have

our first promise and at the end we're

going to add a comma and we're going to

give it a second promise so we'll scroll

down to our second promise here and

we're going to select this code starting

from here

and select the promise right click

copy and at the top we're going to right

click and

paste so we basically created an array

of promises and then we're going to give

this array to

promise.all and it's going to wait for

all of the promises to finish before

going to the next

step so now let's add a next

Step at the end to add a Next Step we're

going to use dot then and brackets and

we'll add a new line to make it a little

easier to

read so as usual dot then adds a next

step to a

promise it will give it a function to

run so brackets arrow and curling

brackets after we load the products and

load the cart we're going to render the

page so let's copy paste that code

inside this next step so we'll scroll

down to the render code and we'll select

it right click

copy and at the top inside then we'll

right click and

paste so now let's comment out our old

promise and try out promise do

all above our old promise we're going to

type

slashstar and below it we're going to

type star

slash and let's

save we'll go to our

console and you can see that it did the

same thing it loaded the products and it

loaded the cart and it's going to wait

for both of them to call resolve before

going to the next step which is to

render or display the page if we open

the page you'll see that everything

displayed

properly so that's

promise.all we can give it an array of

promises and it will run both of them at

the same time instead of waiting for

each promise one by

one also the values that we give to

resolve are saved in a parameter so

inside do then we can add a parameter

called

values and then these values that we

give to resolve are going to be saved

inside here so if we

console.log

values and

save and check the

console and it gives us an array of

values the first value is from the first

promise and the second value is from the

the second promise so here we didn't

give anything to resolve so the second

value is

undefined so that's an overview of

promises and

promise.all promises are a better way to

wait for asynchronous code to finish

versus

callbacks because they help us avoid

nesting and keep our code relatively

flat promises also have more features

like promise all which lets us run

multiple Promises at the same

time now let's save our changes into git

we're going to open the git

section inside cart.

JS we added a function to practice

loading the cart from the back

end and then in checkout.

JS we learn a promises and converted our

code from a callback to a promise

let's type a message describing our

changes learn

promises and convert code to promises

and

commit now that we learned promises

we're going to learn another feature

called

fetch fetch is a better way to make htd

PP

requests let's go back to our

code and we're going to open products.

JS and we're going to scroll down to the

load products

function currently we're using XML HTTP

request to make requests to the back end

and this uses a call

back fetch also lets us make requests to

the backend but fetch uses a

promise so let's do an example and we'll

make the same request except using fetch

this

time we'll scroll up and above load

products let's create another function

using

function and we'll name it load products

Fetch and brackets and curly

brackets and to use fetch we're going to

use the built-in function Fetch and

brackets so this makes an HTTP request

just like we did down here so let's make

the same request as we did in this

function at the bottom we made a get

request to this

URL so by default fetch will make a get

request so we just need to give it the

the URL that we want to make the request

to so at the bottom let's select this

URL and we're just going to

rightclick

copy and at the top inside fetch we're

going to right click and

paste so this will make the exact same

request as we did

below so you can see that fetch is a lot

more simple than XML HTTP request we

don't have to create a new object or do

any setup we can just call Fetch and

tell it where we want the request to

go so this will send a request to the

back end and now how do we get the

response so instead of using a call back

to get the response fetch uses a

promise when we call fetch this is going

to create a promise and we can add a

next step to This Promise using dot then

and

brackets so we'll give dot then a

function brackets arrow and curly

brackets so the way this works is that

fetch is going to send a request to the

backend when we get a response it's

going to go to the next

step it's also going to save the

response inside inside a parameter in

here so we'll add a parameter called

response and this will contain the

response from the back

end so instead of using a call back to

wait for the response fetch uses a

promise to wait for the

response so here let's

console.log the response to see what it

looks

like and now let's run this code

at the

bottom we'll run this function using

load products Fetch and

brackets so now let's

save and take a look at the

console so here's the response that we

get from Fetch if we open it you can see

it gives us a bunch of information about

the response like the status or whether

it succeeded or

failed as well as the URL that we made

the request

to so how do we get the data for the

products from this

response to do that we'll go back to our

code and to get data that's attached to

this

response we're going to use

response. Json and

brackets so this gives us the Json or

the data attached to the response in

this case it's our products

data next response. Jon is actually

asynchronous it returns a

promise so we need to wait for this

promise to finish before we continue to

the next

step to do that inside. then we can

actually return another promise so here

we're going to return this

promise when we return a promise it will

wait for this promise to finish before

going to the next

step so now let's add another step to

This Promise using dot then brackets and

we'll give this a function again so

brackets arrow and curly

brackets when response. Json finishes

it's going to give us the data that's

attached to the response and it's going

to save it inside this

parameter so this response should

contain our products data so let's name

this

parameter products data and let's

console.log this to see what it looks

like so here we

console. log the

products

data and and

save and let's open the

console and you see here that the

products data is the array of products

that we're going to use in our Amazon

Project you'll also notice that instead

of giving us just a big Json string like

before it actually converted the Json

into an array so basically it did json.

pars on the response for us so this this

saved us a little bit of

code finally now that we have the

products array let's do the same thing

that we did down here so we'll scroll

down and select all of this

code and we'll right

click

copy and then up

here we'll remove

this and rightclick and

paste so we'll do the same steps as

before

except using a promise this

time first instead of doing json. pars

on the response we already have the

array of products so we can remove this

and replace it with products

data and then we're still going to

convert this from objects to classes

like before we'll keep this console.log

so we can track the progress

this last line of code let us do

something after we finish loading the

products however instead of using a call

back like before we're going to remove

this

line and to do something after this step

we can actually return this entire

promise so to make it easier to read

let's save this entire promise into a

variable using const

let's call it promise equals

fetch so let's add some new lines here

as well as here to make the code a

little easier to

read so we're basically calling fetch

which creates a promise and then we're

going to save this promise inside this

variable and then at the end of this

function we can just

return the promise so we're just going

to return this whole promise out of the

function and then we can add even more

steps after this

promise so down here this is going to

give us the promise and then we can

attach another step using dot then

brackets and inside here we can give it

a

function brackets arrow and curly

brackets

so this attaches another step to the end

of This Promise so basically attaches

another step

here so after we load all the products

let's just

console.log next

step and

save so we'll check the

console and we'll see that we loaded the

products and then after we did The Next

Step so we can actually return a promise

out of a function and then keep

attaching more steps to that

promise so that's how we use fetch it's

a better way to make HTTP requests

because it uses promises

directly so now let's use fetch in our

project instead of using XML HTTP

request so first let's comment out this

code because we were just practicing

we'll type

slashstar and at the bottom star

slash and let's scroll up to load

products Fetch and we're going to export

this

function so we can use it outside this

file let's

save we'll go to the left

and open checkout.

JS and here instead of using load

products which uses callbacks let's

switch to load products fetch which uses

promises we'll scroll

up and we're going to import load

products fetch so here we're already

importing from products. JS we'll type a

comma load products

Fetch and now will replace load products

so remember that we need to give this a

promise and also remember that fetch

returns a promise so all we need to do

is to remove this code and just call

load products Fetch and

brackets this will return a promise and

we can use it with

promise.all so now let's save

we'll check our

website and you'll see that everything

is still

working so fetch helps us make our code

a lot cleaner because it can return a

promise directly and we don't have to

type out all of this extra

code finally let's use fetch inside our

tests on the left we'll open order

summary

test.js and remember that inside here we

used load products so let's switch this

to using load products fetch instead

first we'll import it at the top we're

importing from products. JS so we'll

type comma and import load products

Fetch and instead of load products we're

going to call load products

Fetch and brackets

so remember that this returns a promise

and we can attach more steps to This

Promise using the method dot then and

brackets and we'll give then a function

to run so brackets arrow and curly

brackets once the products are finished

loading it's going to run then and

inside here we're going to call done to

go to the next step of the test so here

we'll just call done and

brackets and we'll remove the old

code so now let's save to make sure this

is

working and we'll open the tests go to

the browser and open the

test and the order summary test should

be

passing so now let's save our changes

into git we'll open the git set

section inside products. JS we learned

how to use fetch which returns a promise

directly inside checkout. JS we used

load products fetch inside our project

and in order summary

test.js we use load products fetch

inside our tests let's create a message

describing these

changes convert load products

from xhr or XML HTTP request to fetch

and

commit next we're going to learn async

await which is an even better way to

handle asynchronous

code let's go back to our

code and we'll open checkout. Js

currently we're using promises to handle

asynchronous code but the problem with

promises is that it creates a lot of

extra code for example we need to create

a new promise we need to use resolve and

we need to use do

that async await is a shortcut for

promises and it removes all this extra

code so let's do our first example of

asyn a weit we're going to scroll

up and at the top we're going to create

a function using

function and let's name it load page

brackets and curly

brackets and inside we're going to

console.log the string load

page and now we'll learn the first part

of async await which is

async in front of the word function

we're going to add the word async and

space so async makes a function return a

promise so this code is a shortcut for

this code it basically wraps the code in

a

promise so now let's run this function

to show that it actually returns a

promise

So Below this we'll call load page and

brackets and because this returns a

promise we can add a next step to This

Promise using dot then

brackets and we'll give then a function

brackets arrow and curly

brackets and inside here let's just

console.log the string Next Step

now let's

save and we'll check the console so

we'll open the

console and you'll see that we loaded

the page and then in the next step we

displayed Next Step so when we put a

sync in front of function it makes this

function return a

promise this code is a shortcut for this

code

next if we return something from this

function for example we're going to

return a value like the string value

two this gets converted into resolve

value

two so this value is going to be saved

in a parameter in The Next Step so here

we'll add a parameter value and value

two is going to be saved inside here if

we

console.log the value and

save and then check the

console we'll see that value is equal to

this

string and that's it for async it just

makes a function return a

promise now you might be wondering

what's the point of this feature

so the reason we use async is because it

lets us use the second feature called

await await lets us wait for a promise

to finish before going to the next

line so let's do an example inside here

let's run some code that creates a

promise let's run load products fetch so

we'll type load products Fetch and

brackets so this loads the products from

the back end and usually this returns a

promise so one way to wait for this to

finish is to use do then and then give

it a

function so this runs this function

after load products has finished

now await gives us another way to wait

for this promise to finish instead of

using

then at the front we can just type

await so await lets us write

asynchronous code like normal code so

now it will wait for this line to finish

and get the response from the back end

before going to the next next line so we

don't have to do any more do then we

just write it like normal code line by

line this code is a shortcut for this

code and this makes our code a lot

easier to read than what we have down

here so now let's see what this looks

like in the console before we save let's

comment out this promise at the bottom

so we don't get

confused so we'll type

slashstar and at the bottom star

slash and now we're going to save this

code and check the console to see what

it

did so you see that we loaded the page

and then notice that it finish loading

the products before going to the next

step so this actually Waits for this

line to finish before going to the next

line in the code and this makes our code

a lot

cleaner now one very important thing to

know is that we can only use a weight

when we're inside an async

function that's actually the main reason

we use async so that we can use a weight

to make our code

cleaner now that we learned asyn wait

let's use it in our

project so previously we loaded the

products and then we loaded the cart and

then we rendered the page so let's

recreate this using async

await first we want to load the products

which we did here and we're going to

wait for this to finish and then we're

going to load the

cart so to load the cart let's use this

promise down here asyn await can only be

used with promises it doesn't do

anything with a call

back so we'll select this promise and

rightclick

copy and then up here we're going to

load the cart with a promise by right

clicking and

paste so now we want to wait for this

promise to finish before going to the

next line to do that at the front we can

simply type

await finally after we load the products

and we load the cart we're going to

render the page so we'll scroll down and

we'll select this

code and we're going to right click

copy and at the top

we're going to rightclick and

paste and that's it you can see that our

asynchronous code is a lot cleaner now

we load the products and then we just

wait for it to finish then we load the

cart and we also wait for it to finish

and then we run the rest of our code so

we can write asynchronous code like

normal code

so now let's remove the console.log at

the

top and also remove this return value

because we don't need

it and we'll remove do then at the

end and let's

save so now if we open our

website and open the

project you can see that everything

loaded properly

inside the

console you can see that we loaded the

products first wait for it to finish

then load the cart wait for it to finish

and then we displayed the page so that's

how we use a syn8 to make our code a lot

cleaner than what we had

before so now we'll learn some more

details about Ayn a weit

as I mentioned we can only use a weight

inside an async

function also the closest function has

to be

async for example here we have an async

function at the top and inside we have a

normal function so we can't use a weight

inside the normal function we have to

make this one

async another another detail is if a

promise resolves with a value for

example here we give resolve a value

like the string value

three normally this value will be saved

in The Next Step so if we did do then

and gave it a

function this value would be saved in

this

parameter however if we use await this

value just gets returned and we can save

it in a variable so instead of using

then we can Simply Save whatever is

resolved inside a variable using const

value

equals and this makes our code a lot

easier to read instead of having to use

then we can simply save this inside a

variable like normal code

and finally we can use await with

promise.all as well but I'll leave that

as an

exercise so that's async await it's a

shortcut for promises and it lets us

write asynchronous code like normal

code so when working with asynchronous

code a best practice is to use asyn

await over promises and callbacks

because they are much

cleaner so now let's save our changes

into git we'll open the git section in

checkout. JS we created the load page

function where we learned async and

await let's create a message describing

these

changes convert from promises to async

await and

commit now we're going to learn about

error handling when we're sending HTTP

requests across the internet we could

get unexpected errors for example the

internet connection might stop working

so we're going to learn how to handle

these kinds of unexpected

errors let's go back to our code and

we're going to open data/ products.

JS and we're going to

scroll to the load products

function so this uses a call back to

send a request and get a

response now what if there's an error

along the way for callbacks we usually

set up a separate callback just for

errors for example below this we're

going to add another event listener

using xhr do add event listener

brackets and the first parameter is the

event this time we're going to listen

for the error

event and then we're going to give it a

function so now if we get an unexpected

error it's going to run this function so

if we get an error let's just console

log a message

console.log a string

unexpected

error and usually when we get an error

we give some instructions on what to

do here let's just type please try again

later

and

save so this is called error handling if

we get an error during the request we

can handle it with this function so we

just display a

message so now let's try out this code

to simulate an error we're going to

change the url of the

request to

error. superimple backend. deev so this

will create an error because this URL

doesn't

exist so now down here let's call this

function so that we run this code and

get the error so we'll type load

products and

brackets and

save let's check the

console and you'll see that we displayed

this error

message so we got an error and it ran

this error function and it did not run

the load function

above also usually this callback gets a

parameter called error and this contains

some information about the

error so that's how we handle errors

when using callbacks we usually set up a

separate callback just for errors

so now let's remove this line since it

was just for

practice and we'll remove error from the

URL and change it back to super simple

backend dodev and

save next we'll learn how to handle

errors in

promises so we'll scroll up to the load

products fetch

function and this makes the same request

as below

but it uses

promises to handle an error in promises

promises give us two methods do then and

another method called dot catch brackets

and we're going to give catch a function

brackets arrow and curly

brackets so now if this request has an

error it's going to go to this catch

method and it's going to run this error

function so inside here let's also

display a message so let's just copy the

message that we had

below we're going to select this message

and then

rightclick

copy and then inside catch we're going

to right click and

paste and again to simulate an error

we're going to scroll up and change the

url

so we're going to add error at the front

do superimple backend

dodev so now let's call this function

and test out this error code at the

bottom we'll type load products Fetch

and

brackets and

save so now let's open the

console and you'll see in here that we

displayed the error message so we're

successfully creating an error it's

going inside catch and it displays this

message so just like callbacks catch

gets a parameter called error and this

contains information about the error if

we need

it so that's how we handle errors with

promises we have another method called

Dot catch that will run this function if

there's an

error so now let's remove this practice

code and switch back the

URL so remove error and Dot and

save lastly we'll learn how to handle

errors in async

await so let's go to the left and we're

going to open the checkout file so we'll

scroll down and open checkout.

JS and inside here we're using async

await so the catch errors when using

async await we're going to use some new

syntax called try

catch above this we're going to type the

word try and curly

brackets and now we're going to put the

code that could cause an error into try

so here we're making a request to the

back end and here we're also making a

request to the back end so this code

could cause an error so we're going to

move it inside try so we'll select it

right click

cut and then inside here we'll right

click and

paste and now if any of this code inside

a try gets an error we can catch it

using this code at at the bottom we'll

type

catch brackets and curly

brackets Now Catch is going to get one

parameter in these brackets called error

and this contains information about the

error if we need

it so catch Works similarly to catch for

promises if there's an error inside here

it's going to catch the error or it's

going to hand handle the error and run

the code inside catch so in here we can

put our error message so let's go back

to products.

JS and let's copy the error message so

we'll select this and right click

copy and back to

checkout inside catch we'll right click

and paste

so now I'll remove this new line and add

a new line here to make it a little

easier to

read and let's test out this

code to do that we'll go inside

products. JS again and we're going to

modify the URL again so at the front

here we're going to add error do super

simple backend and also we're going to

comment out the dot catch because right

now the error is going to be handled

here and it's not going to be handled

outside in the try catch so we're going

to comment this out using

slashstar and at the

end star slash and

save so we'll go back to checkout.

JS and here we'll also

save and now let's open the console

and you'll see that we had an error here

we caught the error and it ran this code

and displayed the error

message so that's how we handle errors

with async await we put our code that

can cause an error inside try and if

there is an error it's going to run the

code inside

catch so now let's go back to products

and remove error from the URL and the

dot and we'll also uncomment

catch and

save next we're going to learn some more

details about try catch so we'll open

checkout.

JS and one thing to know about TR catch

is that we don't have to use it with

async await we can actually use TR catch

with synchronous code or normal code for

example here we try to run a function

that does not exist and this will cause

an error try catch will catch this error

and display a message so notice that

we're not using async O8 here this is

just normal code so we can use try catch

to catch errors in normal code as well

another detail is whenever we get an

error it will skip the rest of the code

so here it will not console.log next

line it will skip the rest of this code

and go directly into

catch now one thing you might be

wondering is why don't we just use TR

catch everywhere and prevent all of our

errors so try catch and any error

handling is meant to handle unexpected

errors that means our code is correct

but something outside our control caused

the error so we can give some

instructions on what to

do so that's why we don't use try catch

everywhere we only use it for unexpected

errors or errors outside of our

control so the last thing to know about

error handling is that we can man

manually create

errors to manually create an error in TR

catch at the top we're going to use the

word

throw so throw creates a new error or it

throws an error that we're going to

catch a

later and now we need to give this error

a

value so we can use any type of value

for an error like a string number or an

object for an example we're just going

to use a string error

one so this will manually create an

error when we get an error it's going to

skip the rest of the code inside these

curly brackets and it's going to go

straight into catch so this error value

is going to be saved inside this

parameter and it's going to run the code

inside

catch so if we

save and then check the

console throw creates an error and it's

going to display this error message up

here so now let's comment out this

example and

save next if we're using promises there

are two ways to manually create an

error so inside this promise if we want

want to manually create an error we can

also just throw an error like the string

error

2 and this will throw an error and go

inside dot catch by the way if we await

a promise instead of going into catch

it's going to go inside catch

here so await makes it behave sort of

like synchronous code or normal code if

we save

and check the

console it will get an error it will not

load the cart and it will display this

error

message so now let's comment out this

example and we'll learn the second way

to create an error in a

promise inside a promise if we need to

create an error in the future then we

need to use different code for example

here we load the cart and then once it's

finished loading we're going to run this

function so this function runs in the

future inside this function throw does

not work because throw does not work in

the

future instead promises give us another

way to create an error when we create a

new promise it gives us a second

parameter

called

reject reject is a function and it lets

us create an error in the

future so here after we load the cart in

the future let's create an error using

reject brackets and a string error

three so let's comment out resolve as an

example

so now let's

save and check the

console and you'll see that reject

created an error in the

future and then it goes down here and

runs the code inside catch and creates

the error

message so the manually create an error

in a promise we have two ways we can use

throw if we're creating the error

synchronously or right away or we can

use reject if we're creating the error

asynchronously or in the

future so now let's comment out

reject and uncomment resolve and

save so that's error handling it lets us

handle unexpected errors and it also

lets us create our own

errors so now let's save these changes

into git we'll open git inside products.

JS we added. catch for

promises and an error function for

callbacks and then in checkout. JS we

added try catch for async await and we

also learned how to manually create our

own

errors so we'll type a message

describing our

changes learn and error

handling and

commit now that we learned backend

promises and async await let's use them

in our

project we'll open our

project and open the tab for the project

and we're going to go to the checkout

page so the feature we're going to work

on is in the checkout page we're going

to make this place order button

interactive when we click this button

it's going to take our cart and turn it

into an

order this time instead of writing this

code ourselves we're going to use the

back end to create an

order so first let's set up an event

listener for this button we'll go back

to our

code and open our files

and that button is in a section called

the payment

summary so we're going to open scripts

SL checkout payment summary.jpg

your order and now we have the code for

the button right here so we're going to

set up an event listener so we can do

something when we click

it first we'll add a class to the button

so we can get it in our

JavaScript at the end of the class let's

create a new line and add a class

js- Place Das

order and now after we put this HTML on

the page we're going to set up an event

listener to do that we're going to get

this button into our JavaScript using

document. query

selector

brackets and a string and to select this

class we're going to start with a

js- place-

order and now that we have this button

we're going to add an event listener to

to it so we'll create a new line and use

the method do add event

listener

brackets and we'll give this two

parameters the first parameter is the

event we want to listen for which is

click and the second parameter is a

function we want to run when we click

this button so we'll type brackets arrow

and curler brackets

and now when we click this button we're

going to make a request to the back end

to create the

order so for this example I set up a URL

path in my backend for creating orders

called slash

orders so inside here we're going to

make a request to the backend using

fetch

brackets and then we're going to give it

the URL of the request which is H ttps

colon double

slash super simple

backend. Dev and the URL path slash

orders however this time we need to send

some data to the back end so we need to

send our cart to the backend in order to

create an

order to send data in a request we need

to use a different type of requests so

there are four common types of requests

get post put and delete get means we

want to get something from the back end

post means we want the back end to

create something put means we want it to

update something and delete means we

want to delete something so far we only

use get request which let us get data

from from the back

end however get requests don't really

let us send data to the back

end so in this situation we want to

create an order so we're going to use

post to create something post lets us

send data to the

backend so to create a post request

instead of a get request we're going to

give fetch a second

parameter which is an

object and inside this object we're

going to give it a property called

method

colon and this is the type of the

request in this case we'll use the

string

post and after this we're going to give

another property called

headers colon and this is going to be an

object

headers gives the backend more

information about our request and this

is needed when we're sending data to the

back

end inside this object we'll add the

property string Capital C content Das

capital T

type

colon and the value will be the string

application slash Json

this tells the back endend what type of

data we're sending in our request here

we're going to send some Jon which is

basically a JavaScript

object next we're going to add another

property called body

colon and this is the actual data we're

going to send to the back

end according to the documentation we

need to send an object with a property

called cart and this contains our cart

array so in the body let's send an

object with a property called cart colon

and give it the cart

array so we should have the cart array

in this file and it should be called

cart and finally we can't send an object

directly in our request we need to

convert it into a Json string

to do that at the front we'll use

json.

stringify Open Bracket and close bracket

so this will convert this data into a

Json string and now we can send it to

the back

end okay so after we send this request

we need to wait for the response to come

back to do that fetch returns a

promise however instead of using dot

then to add a Next Step let's use async

a weit because it's cleaner so first we

need to make this function

async remember we can only use await

inside an async

function so at the front of this

function we'll type the word

async and now in front of fetch we can

use

await this is going to wait for fetch to

finish or for fetch to get a response

from the back end and then go to the

next

line now because we used await we can

save the response in a variable so at

the front we'll create a variable const

and call it response and make it equal

to this result

next remember that to get the data

that's attached to the response we need

to use response.

Json so down here we're going to use

response. Json and

brackets now remember that response.

Json is also a promise so at the front

we can use await to wait for this

promise to finish before going to the

next line

so this will give us the data that's

attached to the response which should be

the order that was created by the

backet so let's save this in a variable

using const order

equals and finally let's

console.log the order to see what it

looks like so now let's save

and then we'll open the

project and make sure you have some

products in your

cart and then we'll click place

order and now we can check our console

to see what the order looks

like and you'll see that we got an order

object from the back end it has an order

ID an order time and the products in our

order including a delivery time and the

quantity that we

want so we successfully use the back end

to create a new

order let's also check the network tab

up here and open

network so I'll resize this to make it a

little easier to read and we'll search

for the super simple

URL and then we'll find this request

orders with a status 200 and we'll click

it so inside the details you'll see that

it was a post request sent to/ orders

and the status code was 200 so it was

successful inside the payload tab this

is what we sent to the back end which is

our

cart in the preview tab this is what the

backend sent back an order object

and the response tab is the same thing

we got the order object

back so that's how a real world website

works instead of creating the order on

the web page or on our computer we send

an HTTP request to the backend to create

the

order okay now that we created an order

let's save it

somewhere we'll go back to our

code and on the left inside the data

folder let's create a file for our

orders so we'll click inside this folder

and then click here to create a file and

let's name it

orders. JS and press

enter at the top let's create an array

to contain rain all of our orders we use

const orders equals and empty array and

let's export this so we can use it in

other files

export next let's create a function for

adding an order to this array so we'll

create a

function add

order brackets and curly brackets and

we'll give this function an order object

and we're just going to add it to the

array now for orders we usually want the

most recent order at the top so we're

going to add this order to the front of

the array to do that we'll type the

array name orders and use the method do

unshift

brackets and we'll give it the

order so this will add the order to the

front of the array instead of the

back finally let's save our orders into

local storage so we'll create a function

to save to local storage

function save to

storage brackets and curly brackets and

we'll run local

storage. set item brackets and a string

we'll use a local storage key orders

comma and remember local storage only

supports strings so we'll use

json.

stringify

brackets

orders and now when we modify this array

we're going to save to storage and

brackets finally at the top let's load

the orders from Storage

so

here we use local

storage. getet item brackets the string

orders and remember that this will be a

string so we need to convert it back

into an array using the code json. pars

and

brackets now in the beginning we're not

going to have any orders saved in local

storage so we can give this a default

value using or and an empty array so if

there's nothing in local storage it's

going to use this empty array as a

default and

save so now let's use add order in the

payment summary so first we'll export

this

function and and

save and then open the payment summary

again and at the top we're going to

import that function so here we'll

import curly brackets add

order from a

string and we'll go into the data folder

which is do do slash

dotdata SL orders

doj and and we'll scroll back

down and now after we create an order

from the back end we're going to add it

to the array and save it in local

storage using the function add order

brackets the order

object and

save now if we go to our web page and

click place

order this should create an order order

from the back end and save it in local

storage so now we can open our

console and go to the console Tab and

let's check if it's inside local storage

using local

storage. getet item brackets and the

string

orders and press

enter and you'll see that we saved an

order in local store

storage if you ever want to remove the

orders from local storage you can use

this

code local

storage. remove item brackets and the

string

orders press enter and then refresh the

page let's go back to our code

and let's get some practice and add some

error handling to this code so at the

top for asyn of weight we're going to

use try catch so we'll type try curly

bracket and catch brackets and curly

brackets and catch gets a parameter

called

error so now we're going to move our

code inside a try we'll select this code

and then right click

cut inside try right click and

paste and I'll create a new line and now

if we make a request and there's some

sort of network error that error will go

down here and we'll run the code inside

catch so in here let's display a

message

console. log the string

unexpected

error try again

later the last step is after we create

an order we should go to the orders

page to do that at the bottom

here we're going to use an object called

window.location window.location is a

special object object provided by

JavaScript and it lets us control the

URL at the top of the

browser if we change the location object

it will change the url at the top so

let's give this a try we'll go into our

code and we'll type

window.location Now location has a

property

called href

this gives us the URL at the top of the

browser and if we change the href

property it will change the url at the

top of the browser so we'll try that in

our code we're going to change. href and

make it equal to the string orders.

HTML so this will replace everything

after the slash here with orders.

HTML and this will open the orders. HTML

file which is at the bottom

here and this will open the orders

Page by the way orders. HTML is a file

path the current file is checkout. HTML

because this code is running on the

checkout page so it starts from

checkout. HTML and then looks for a file

called orders. HTML beside it which is

this file here and it loads this file in

the

browser so now let's

save we'll open the project and then

click place

order so it should create a new order

using the backend and it will take us to

the orders

page so right now we have a list of

order objects and that's all the data

that we need to create this page I'll

leave generating the HTML and making

this page interactive as

exercises so now let's check our tests

to make sure that everything is still

working we'll open the tab for our tests

and I'll refresh just in case and it

looks good and we'll save our changes

into git we'll go to the git section

inside orders. JS we created some

functions for saving our orders and in

payment summary.

JS we made the place order button

interactive and we use the backend to

create an order let's create a message

describing these

changes create order using the back end

and

commit so we're going to learn one more

thing in this lesson and this is needed

to create the tracking page we're going

to learn how to use URL

parameters so first let's open our

project and we'll go back to the orders

page and on this page we have these

track package links beside the products

if we click this link it will take us to

the tracking page at tracking.

HTML however right now this page is just

plain HTML there's no

JavaScript so if we go back to our

orders and then track a different

product you'll notice that all of the

tracking pag pages are the

same so we need to make each tracking

page different depending on the order

and the product so how do we know which

product to track on this

page to create this we can use a feature

called URL

parameters URL parameters let us save

data directly in the

URL to create a URL parameter at the top

after this URL we're going to type

question mark and then order capital i d

equals 1 2 3 for example and press

enter so the question mark means we're

adding a URL parameter to this

URL so a parameter is a property value

pair the left side is a property and the

right side is a value

this is sort of like an object like

this so using URL parameters we can save

some data in the URL like

this and then we can use JavaScript to

get this data out of the URL to do that

we'll go back to our

code and we'll open our files here and

we'll scroll down to the bottom to the

tracking

page and let's scroll all the way down

to the

bottom and at the bottom of the body

let's add a script tag to run some

JavaScript so we'll type less than

script greater

than and to get the parameters out of

the URL we can use a built-in class

called

URL first let's generate an object using

this class we'll type

New Capital URL and

brackets and we'll give it the URL that

we want to get the parameters

from so in here we'll type

window.location.href

remember that

window.location.href gets the URL at the

top of the

browser and now let's save this object

in a variable

at the front we'll create const URL

equals this

object so this URL class analyzes the

URL that we give it and breaks it down

into different parts one of the parts

are the URL

parameters to get the parameters we're

going to use a property

url. search capital p perams

by the way URL parameters are also

called search

parameters because they're used for

features like YouTube

search so search params will let us get

the URL parameters up

here so let's say that we wanted the

order ID

parameter inside our

code search params has a method called

Dot

get brackets and this lets us get

individual parameters so inside here

we'll give it a string and we'll get the

order capital i d parameter out of the

URL so let's console.log this

console.log and

brackets if we

save and then open our project and go to

the tracking page and then open the

console right click

inspect the

console you'll see that it gave us the

order ID that we saved up

here so using that code we can get URL

parameters out of the URL at the top and

then use them to create this

page we can also say save multiple

parameters in the URL to save another

parameter at the end we can just type

and and now we can give it another

property value pair like product Capital

ID equal

456 and press

enter and now inside our code we can get

this second parameter

so inside here we're going to make a

copy of this line select it right click

copy and then down here right click

paste and this time we're going to get

the

parameter product Capital ID and

save if we open the page and open the

console

we got the order ID as well as the

product ID out of the

URL so URL parameters lets us save

different data in each

URL and we can actually go back and

forth between them so if we click the

back button it will go to this URL and

this URL has different data or

parameters saved inside if we click

forward this URL has different

parameters or data saved

inside and this is how YouTube search

works if we search for something our

search is saved as a URL parameter if we

search for something else our search is

also saved as a URL parameter and we can

go back and forth between the

two so this is actually all the data

that we need to create the tracking page

we need to know which order it is and

which product it

is now there's one more thing to know to

create this page we'll go back to our

code and we're going to open the orders

page at orders.

HTML and we're going to find the track

package button using control F or

command F and we'll type the text in

that button track

package so notice that these buttons are

just a link to the tracking page or

tracking.

HTML so when you're generating this

HTML make sure that you add URL

parameters after this tracking page

URL using question mark the order

Capital ID equals and then you

substitute the order ID like 1 2 3

and then and also attach the product ID

product Capital ID equals

456 so when generating this HTML make

sure you substitute the order ID and

product ID into this URL so that when it

opens the tracking page you know which

order and which product to track

I'll leave generating the HTML and

making the tracking page interactive as

exercises so now let's save this

file and let's check our tests so we'll

open the browser and open the test Tab

and everything is still working and

we'll save these changes into git open

the git

section in orders.

HTML we added an example of adding URL

parameters to the tracking page

Link in tracking. HTML we added an

example of getting the parameters out of

the URL at the

top let's create a message describing

these

changes add URL

parameters

example and commit

and that's the end of this lesson in

this lesson we learned what a vend is

and how to make HTTP requests to the

back end we learned how to use XML HTTP

request and

fetch we learned how to handle

asynchronous code using callbacks

promises and async await we learned how

to test asynchronous code we learned

about error handling for unexpected

errors we use the backend in our project

and we learn URL

parameters before we look at the

exercises you might be wondering what's

the next step after this course instead

of just using a backend the next step is

to learn how to create our own backend

to do that you need to learn the command

line and after that you'll learn a

technology called nodejs which lets us

create our own

backend also after this course you can

learn how to put a website on the

internet using this video right

here here are some exercises that'll

help you practice what we learned in

this

lesson e

thanks for watching here are some other

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the next one