All language subtitles for English (auto-generated)_en_0_Practical TypeScript – Course for Beginners(1080P_HD)

John smilga teaches this course about

the Practical applications of typescript

typescript is a strongly typed

programming language that builds on

JavaScript this is an excellent course

for people who want to learn typescript

hey what's up it's John from coding anic

and welcome to practical typescript

course we all focus on practical

applications of typescript so you can

start using it effectively in your

projects right away during the course

we'll cover everything from setting up

your development environment to

deploying your typescript applications

the course consists of three major parts

first part typescript fundamentals where

we'll explore basic types interfaces

classes generics and rest of the good

stuff second part react and typescript

where we'll integrate typescript into

react projects create typed components

and manage state with typescript and the

third part

is where we'll put our typescript

knowledge to good use and build a modern

store application with typescript shat

UI and react router if you wish to

explore all of the features of the store

project it's located at this URL

typescript comy sloth ny. apppp again

the URL is typescript comy sloth ny.

apppp quick sign not during this video

will only cover Parts one and two so if

you enjoy the content and wish to work

on the big project as well consider

enrolling in the full Course located at

coding addict IO again the full course

is available at coding addict IO okay

and first let's recap that JavaScript is

considered Loosely or dynamically typed

because variable types are determined at

runtime and can change as the program

executes this means you don't have to

declare the type of the variable when

you create and variable can hold values

of different types at different times so

the following code is a valid JavaScript

code however where are we going to

encounter an error if we try to run this

code correct at runtime and this is

manageable if you have few lines of code

but the bigger the project the more

challenging it will be

to spot such technically innocent bugs

and this is where typescript enters the

picture because it is a programming

language that builds on JavaScript by

adding static typing this means you can

specify things like types of variables

function

parameters return values and some other

things to help catch errors early and

improve the code quality it is a super

set of JavaScript so yes all the

JavaScript code is also a valid

typescript code now one way to think

about it is as follows by using

typescript in our project we'll still

write the JavaScript we already know but

with some elements or sprinkles of

typescript and these elements will act

as safeguards or constraints to help us

catch potential errors more quickly and

without the need for 10,000 console logs

when we introduce typescript to our

project we will write our app in the TS

or in the case of react in the DSX file

there will be a compile or transpile

step where all of the typescript code is

transpiled to good old JavaScript code

and at the end since it is a vanilla

JavaScript code we can run it anywhere

quite often you'll hear people say

something along the lines of well once I

built my first project with typescript

it was very hard to go back and build

with just vanilla JS and even though I

was also very skeptical of such

statements I can verify that it was the

same in my case yes typescript still has

learning curve and yes it involves more

work but at the same time you'll notice

how how you're able to fix bunch of the

errors quickly at build time without

running around like a headless chicken

before we set up a brand new typescript

project I want to mention a few useful

things if you're confused about some

topic or simply want to research a

concept in more detail a good place to

start is typescript docs which are

located at typescript l.org again the

URL is typescript l.org also in there

under the playground tab you will find a

Nifty code sandbox or typescript

playground which I might utilize from

time to time during the course to

underscore some particular point it

works as follows on the left side we

write a valid typescript code and we get

back the resulting JavaScript code now

you won't be able to build the entire

project in there but it is a very cool

option if you you quickly want to test

something as far as the code editor I'm

going to use VSS code and since it's

practically an industry standard these

days my assumption is that you'll use

the same one since I record courses I

use the very basic default theme and

when it comes to my extensions I will

mention some useful ones once there is a

need during the course in order to work

with typescript you will need no

installed on your machine again

something I assume you already have done

but if it's not the case please visit

nodejs.org again the URL is nodejs.org

pick your operating system and follow

the install steps also during the course

I'm going to reference the main course

repo where you'll find source code

challenges notes useful references and

tons of other useful stuff so I highly

suggest getting a hold of the repo

before you continue with the videos just

look for my GitHub profile and under the

repos search for typescript course

repository there are few ways how we can

add typescript to our project since it's

available as an npm package we can

install it globally or on the per

project basis set up the configuration

and run the compile step manually the

this is definitely an option but we're

going to take a different approach which

is going to

be pre-built template because at this

point at least in my opinion it's a more

realistic scenario chances are whether

you want to build a nextjs or remix or a

good old react app there will be already

a template that contains the technology

you want to use as well as types

configuration so more often than not

your job will be to write a valid code

instead of losing your sleep over

correct configuration setup for this

course I picked V since it's one of the

most popular build tools out there but

please keep in mind as far as the

typescript logic is concerned it's the

same if for example you're going to use

nextjs with a typescript template now we

want to run one command in order to set

up our template and I'll show you two

places where you can get the command

First Option you can navigate to V docs

which are located at bejs

dodev then click on getting started and

pretty much you're looking for this

command and then we just need to pick

the template and since my npm version is

bigger than seven I'm going to run my

command with the Double

Dash now as you can see we have tons of

templates available and the idea is

following we go with npm create V latest

then project name then Double

Dash go with the template one and pick

the template as you can see we can go

with reacts as a say not something we're

going to use in the part two and three

we can also for example set up The View

with typescript and we're actually going

to start the course with vanilla

typescript template so this is just

going to be an application built with

vanilla JavaScript we're not going to

use react and uh to tell you honestly we

don't really care about the template we

just want to use it in order to learn

typescript so pretty much most of the

first part of the course will spend in

one file and you'll see what I'm talking

about in a second now remember in the

previous video I mentioned the main

course

repo navigate over here and then look

for typescript tutorial and under this

directory look for read me and here

you'll right away get the command and as

a this is something that I'm going to

copy in literally a few minutes and I

suggest actually doing the same because

in here again you'll find find all of

the notes and challenges and all that

cool stuff so if you want to save

yourself time on typing just navigate

over here and grab the command again npm

create V at latest then at least in my

case the project name is going to be

typescript then double dashes then

template and we're going to go with

vanilla DS so let me grab the

command let me navigate I guess to

desktop and and I'm going to zoom

in then let me set up my

command and once I have successfully

installed the project on my machine I

want to open up my text

error drag and drop the folder and next

we'll take a look at the files and

folders available in this template as

far as the files and folders we've got

over here a public one so this is where

we can place the public assets then we

have a S one essentially this is where

we'll do all of our work a get ignore

where we specify which files are going

to be ignored by The Source control then

index HTML which is actually going to be

our homepage also a package Json

something we're going to cover in more

detail in a few minutes and also a TS

config which we'll cover in Greater

detail later on in the course and before

we take a look at the specific

files and cover the build step here are

a few things I want to do first since

it's a node application we do want to

install the dependencies so effectively

just open up the integrated terminal and

run npm install now also again I highly

suggest getting the readme since in my

opinion you will find find it super

useful as you're following

along so just navigate back to the

project and somewhere create a read me

markdown one and just paste the contents

over here save it and once we install

dependencies now we also get the node

modules so this is where all of our

dependencies are located then we want to

go with npm run Tav which is going to

spin up our project in local development

and we're looking for Local Host

5173 and this is what we should see on

the screen so essentially there's some

images over here a text as well as the

counter now if I'm being perfectly

honest like I mentioned previously we

really don't care about the actual

vanilla JS application I believe towards

the end of the first part of the course

yes we will build a tiny app but most of

our time we'll spend over here in a

source one in one specific file called

tutorial DS where effectively we will

just learn all the typescript

fundamentals now if we take a look at

the package Json we see that we have the

dev one this is the command we just

invoked and also there's a build one now

before we run

build I do want to create a file and

showcase how our setup is going to look

like now one interesting thing that I do

want to point out notice how before the

build command they actually invoke

tsnc so notice how typescript is a Dev

dependency so before the project is

built first it's compiled so that's the

step I mentioned previously where we're

going to write all of our code in the

files with Ds extension and once we

perform the build step it's going to

spit out the vanilla JavaScript code so

if we take a look at the index HTML like

I said this will be our homepage so for

example if you want to change the title

it's definitely an option then they have

over here this div with an ID of app and

effectively in a second you'll see how

in the main DS they in

Jack the images the divs and all that

into this app one so now let's navigate

to the main DS in here they import

styles again something we're not really

concerned with also two images the

typescript one and V1 and also a counter

and then they

select div with an ID of app and like I

said they dynamically inject the

elements into the d as you can see there

are some already sprinkles of typescript

and essentially this is something that

we're going to cover during the first

part of the course but most of the logic

should look very familiar correct

because this is straight up JavaScript

again with just sprinkles of typescript

now if we take a look at the counter

it's going to be same idea this is

straight up JavaScript with the only

difference that now we're looking for

element and actually we specifically say

that the type is going to be HTML button

element now how is our setup going to

look like since I said that I mean we

really don't care about this code and to

tell you honestly we're not actually

going to look too much in a browser

either most of the time will spend in

the error well in here in the source I

want to create a new file in my case I'm

going to call this tutorial TS the name

is totally up to you just make sure that

you add the TS extension so we're going

to go over here with tutorial then TS we

create a new file and for now I just

want to log just so I can see that

everything works and I'm going to go

with typescript and then tutorial let me

save it and then in order for this code

to run we just want to navigate to Main

TS and we just want to import a file

that's it we're not going to do anything

else we'll simply go with import and now

we're just looking for our TS file so

tutorial and TS and the moment we do

that once we navigate to the browser if

everything is correct we should see that

console

log and if that's the case we are in

good shape and before we move on to

typescript fundamentals let me show you

the result of the build step again let's

just recall that before V our build tool

builds the production ready application

it's actually going to compile our code

which essentially just means that all of

the typescript elements we're going to

have in our code are going to be

transpiled to good old vanilla

JavaScript and essentially during this

video I just want to showcase that so

don't worry about the code I'm going to

write in fact you don't have to follow

along I just want to showcase the end

result so let's say if we're going to

add something typescript for example

interface of course something we're

going to cover during the first part of

the course and I'm going to go with name

String and ID number and as a sign note

essentially it's just a shape of an

object and then I'm going to create the

object and I'm going to go with some

value so add the type over here and now

I just need to provide name which has to

be a string now so I'm just going to go

with random and comma and then we're

going to go with ID and then one two 3

and then let's also log so let's go with

some object so once we navigate right

now to a terminal we have few options if

you want you can always stop the dev

server and essentially you do that with

contrl C or you can just open up a new

terminal window and that is going to be

my Approach so essentially now I want to

go with npm and not Dev but we're

actually looking for build so we run

this command if we don't have any

typescript

errors we're going to be successful and

now notice we have this this folder so

this is our production ready application

we still have index HTML okay everything

is beautiful and then in the assets

we'll have the index JS so this is

essentially our application in vanilla

JS and if we take a look at our code so

notice I have this console log

typescript tutorial so I clearly know

that it's coming from our file notice

there is no interface anymore again

there is some kind of minified object

over here and effectively we also conso

log it that's it so there is no

interface there is no type string or

type number or in fact any of the other

stuff that we have here as far as the

typescript elements so again essentially

we'll write all of our logic in files

with Ds or DSX extension if we're

working with react and then once we

build our project

we're going to get back our good old

vanilla JavaScript code which

essentially we can run anywhere so

hopefully it's clear what's happening

during the build process so now let me

clean up our project first I want to

remove the disc folder then also I'm

going to remove my second terminal

window and at the very end I just want

to remove this code from tutorial yes so

this is going to be our starting point

essentially we have console log in

tutorial DS and if we take a look at the

browser we should see over here

typescript tutorial and if you have the

same result now we can move on to the

next task okay and let's start our

typescript journey by discussing type

annotations which allow us to

specify the variable type so let's say

in my project I have a variable by the

name of awesome name and if you have

watched any of my courses and tutorials

you know that the most awesome name ever

is shake and B since I'm working in a

typescript project I can actually

explicitly set up the type and the

syntax is following we go with colon and

then since I want this to be a string I

type string now there are quite a few

types and I'm not going to list all of

them I really find it pointless

essentially the most straightforward

ones are string number and Boolean and

again the syntax is going to be the same

so we just go over here with the colon

and then the type and of course as we're

working through the course we'll get to

know the other types as well and the

moment I set this type for my

variable I get two things out of the box

essentially it can never be something

something else so I can go to the next

line and set it equal to a function and

also I'll WR way get the methods that

are associated with this type so in this

case it's going to be a string so just

to demonstrate that if I go to the next

line and if I set it equal to a value of

something this is still valid why well

because type is string so everything's

correct correct also I can go to next

line and set it equal to awesome Dot and

notice right away I get only the methods

that are

associated with the typ string which

again is super awesome because

essentially I avoid some unnecessary

bugs so in this case I'm just going to

go to application and now if I log this

value if I go with awesome name and take

a look at my console if everything is

correct should be equal to a something

so we set it equal to different string

value and then we ran the two uppercase

method now one thing we canot do is

something like this where I go with

awesome name and set it equal to 20

which is a different type so notice

immediately typescript starts yelling at

me type number is not assignable to a

type string and I want to repeat the

same thing for the number as well as the

bullion so just so it's clear we're

going to start with some kind of

variable in my case I'm going to go with

amount I'll set it equal to a number and

again I can do anything that's allowed

with the numbers for example and set

equal

amount 12 minus 1 something like that

but cannot set amount equal to pens

that's not going to work right away

typescript is going to be super helpful

it's going to say Hey listen you said

this is going to be the number so yeah

you can run the number methods you can

do calculations but you cannot just

reassign it to something else lastly

let's take a look at the Boolean pretty

much same

deal we're going to go with is awesome

we're going to add a colon set up a

Boolean type for Star it's going to be

true then we're going to set is awesome

equal to false and then let's try to set

it equal to shake and bake again the

most awesome name ever so we're going to

go with is

awesome and let's go with shake and bake

again cannot do it because the type is

bulling and essentially in the process

we're just avoiding this entire

debacle where initially it can be one

value then three lines later it's

something else and then we're turning

into a third thing and then start

running some methods on it

essentially this is static so now we say

Hey listen this is going to be string

and string only same goes for number

Boolean and in the process we just avoid

bunch of unnecessary bugs that come from

typos that come from just using wrong

methods and that sort of thing and

before we work on our first challenge

let me quickly mention something

typescript is actually really smart and

can infer the type of the variable based

on the values when it's defined now the

fancy name is type inference but

essentially for us it just means that we

can remove all of these type annotations

and we'll still get all of the goodies

that I covered in a previous video so

now if I hover over the awesome name

notice how based on the value when the

variable was defined typescript can

nicely infer the type so in this case

it's string then it's the amount and

then when it comes to is awesome

typescript knows that it's a Boolean now

don't dismiss the type annotations we're

still going to use them but most likely

not for such straightforward variables

type inference also has some gotas

especially when we start working with

more complex values so yes typescript is

always going to try to help you when it

comes to functions when it comes to

variables it will try to kind of get the

type based on the value and obviously

it's super awesome because it saves us

time notice I don't have to go to Every

variable and just make sure that the

type is set but there are some

questiones we need to aware of and don't

dismiss type annotations because we're

still going to use them throughout the

course just not four variables like this

okay and now it's time for our Challenge

and since it's our first one I will

cover the steps as well but with the

future challenges just so we can save

little bit of time I will most likely

right away start working on the solution

also since it's our first one it's going

to be extremely

straightforward I just wanted to get the

ball rolling just so we get used to this

idea that we learn some stuff and then

we work on some kind of challenge so I

want you to create a variable of type

string and try to invoke a string method

on it then same is going to be with a

number create a variable and try to

perform a math operation also I want you

to create the Boolean one and perform

The Logical

operation and then try to just assign

some values to those

variables that are different types so

just try to come up with something that

shouldn't supposed to work and see

whether typescript complains about it

now you can use the type adaptation or

you can also use the type inference

that's totally up to you again super

straightforward challenge where just

want to navigate to tutorial I want to

come up with some kind of variable for

my string in my case I will use the type

annotation don't ask me why just think

that it's going to be better in this

case so I'm going to go with hello and

then let's go with

typescript okay beautiful then let's run

the two oper case so greeting is equal

to greeting dot then two uppercase let's

invoke this this should work we should

have no issues and as long as I don't

have the red squiggly lines I'm good to

go so typescript is not yelling at me

then also let me set up the age so in

this case it's going to be a number I'm

going to set it equal to 25 then let me

add a five to it okay also works

everything is beautiful and then we want

to go with is adult so that's my Boolean

let's add a type annotation here AG is

let's say bigger or equal to 18 now this

should be true and you know this is the

case where I will log it so let's see is

adult is true yep that's the one so now

let me just set it equal to the opposite

I'm going to go with his adult is equal

to opposite is adult again let's log it

and now it's going to be false and and

then somewhere here let me just try to

set the greeing equal to 10 that

shouldn't work also we can go with age

and set it equal to 30 so string again

we're going to get the error and lastly

we have the is adult and I'm just going

to set it equal to yes and as you can

see all of them result in errors so

again we have one type and typescript is

not happy when we just randomly decide

that our variable is going to be of

different type all right and before we

continue with tutorial let me show you

something interesting about the setup

you see even though we have these

typescript errors over here we're going

to be able to run our project locally so

what am I talking about well if I go

here and set up the console and log and

in my case I'm just going to look for

all three values So reading age and is

adult if we navigate to a console you

can see first of all that all of the

variables have the values that they're

not supposed to so typescript is

complaining but it's still works and

also notice how our project didn't crash

we're just getting these typescript

errors correct so here's the deal when

we're working with typescript actually

project is going to work even with the

errors locally but whenever we want to

host a project what do we need to do

well we need to build it that's usually

the setup and in order to build it we'll

have to pass the typescript checks so if

we try to build with typescript errors

we're going to fail and as a result we

won't be able to host the project let me

show you the package Json notice over

here

so we have Dev command which essentially

just spins up the dev server and we also

have the build command and remember

before we even run feed build we

actually compile this with typescript

and again if we have some errors we

won't get the I believe it was this

folder where we have the static assets

which in turn are going to be used to

host our project so let me showcase that

just so we are on the same page first I

want to stop the dev server let me run

npm run build so at the moment I have

the errors typescript errors and

immediately I just get back these error

messages in my console so in order to

fix it what do we need to do well in

this case it's sort of simple where can

just comment them out delete them

whatever doesn't really matter again let

me clear everything

here let me run the last one npm run

build and now since I don't have any

typescript errors notice I have the this

folder and this is where I have my

production ready application so again

locally even with typescript errors

you'll be able to run the project

however you have some issues once it's

time to to deploy it once it's time to

build the production ready application

and up next let me introduce you to a

union type which allows a variable to

hold a value of multiple distinct types

for now we're just going to take a look

at some basic examples but since Union

types are super powerful it's not the

only time you'll see them in the course

so once we start working with functions

or and all that yep we're going to use

the union type as well so let's imagine

I have a variable by the name of tax and

typically it's a number correct so I can

set it equal to

10 typescript can nicely infer the type

and I'm good to go but let's imagine

that whether I'm getting it from the API

or whether user provides that value it

can also be a string I can go here set

up my colon then go with number so it

will definitely be a number and I can

use this pipe operator and then I can

just add another type which in my case

is going to be string now please keep in

mind you can add 10 another types but I

mean in our case we're just going to

stick with two but yeah you can go here

and add for example Boolean it's

definitely an OP option so now I can go

to a next line and I can set it equal to

a 100 and typescript is not going to

complain because yeah one of the types

is actually number now I can also go

here and set it equal to a string and in

my case I'm going to go

with uh let's go with $10 over here so

both of them are valid because now I

have Union type where it can be either a

number or a string now once we start

working with more complex examples yes

we'll have to do some checks and all

that so all of that is coming up but

this is a super powerful concept where

essentially we can say to typescript hey

this is going to be either this or it's

going to be the another type now also

something that I was blown away is the

fact that we can set up the literal

value type so that's the fancy name

essentially it just means that I can

provide the literal

values let's imagine we have a

request status so that's my variable now

what are the typical values for the

request status well quite often it's

pending success and error so for

starters I can just go here with pending

so that will be my initial value then go

with the colon and now I can just

provide the potential string values

which are going to be pending then again

I use the pipe

operator I provide success then another

pipe and I'm going to go with error and

what's super super cool is the fact that

whenever I work with this request status

notice I right away get these

suggestions so it can either be error

pending or success and

again it helps me to avoid errors

because it's way harder to mistype

something and also I kind of just go

here and say random I mean first of all

it doesn't match my suggestions and

second right away typescript is going to

complain so I don't have to find doubt

about this bug in the runtime I actually

can see it right away as I'm building

the project so let me go here with

success error is going to work so

there's nothing wrong with that but if

I'll try to set it equal to random as

you just saw I mean typescript is not

going to be happy about it topic we're

going to come back to when we set up

more complex examples and again Union

types allow us to set up multiple types

for the same variable and while we're

still in a roll let's also cover type

any which allows us to opt out of the

type checking so I'm going to create a

variable and I'm going to name it not

sure so not sure now I will set it equal

to four and since we already covered

that typescript can infert a Type we'll

see over here this number but I can also

go with colon and set up any over here

now any means exactly what the name

implies this going to be anything I can

set it up equal to function string

Boolean whatever so in next line can say

you know what not sure is actually going

to be a string maybe a string instead

then on next line I can set it equal to

false and as you can see that script is

not

complaining now as you're looking at it

probably the first thought is well wait

a minute that's

how variables behave in JavaScript and

you're absolutely absolutely correct now

as with everything in programming

there's bunch of fights over it whether

you should use any at all as far as my

two sents be very careful when you

introduce any to your

application because it can spread like

wildfire so you started off with setting

up one variable type any and then next

thing you know you have any all over

your application because for example

when you return any from the function

then the result is any and on and on and

on and on so definitely have a good

reason why you want to use any and as I

note any is something you'll see quite

often when typescript is trying to come

up with a type but we haven't provided

any clues for example if I'm just going

to go with some random and I'm not going

to set up the value as you hover over it

notice now this is going to be type any

so this is something we quite often get

by default when typescript is trying to

get the type but I mean I haven't

provided any clues what this value is

going to be and this is essentially

something that we'll constantly try to

fix where for example for functions

implicitly it starts with any but we

don't want it to be any we want it to be

some kind of type so just be careful

when you use it it's definitely an

option it's useful if let's say you want

to test something it's also useful if

you have a pretty big codebase and you

just slowly want to introduce typescript

so you still want to run the project but

you slowly want to add it to your

project yeah it's definitely the case

just again be very mindful when you set

something any because next thing you

know it half of the application is going

to be any and then at that point I mean

it kind of loses the sense to use the

typescript in the first place again

those are just my two scents if you go

to Google you'll find definitely way

stronger opinions but let's just leave

it at that and let's move on to the next

topic and next let's see a practical

application of type annotation where

essentially I have a list of books so I

just have some strings over here and I

also have a variable which at the moment

is undefined and there's no type since

again I want to showcase what type is

going to be set by default and I want to

set up a loop where I iterate over and

then if it matches one of these titles

over here then I'll set the variable

Found book equal to that title so first

let's set up the loop I'm going to go

with four off Loop so lead book off

books then we're going to set up the

condition so if book and I think I'm

going to go with the

first string over here so I'm going to

go with 1984 if that's the case then

phone book is going to be equal to a

book and we're also going to break out

so let's add the break keyword let's

save it if everything is correct this

should be equal to a title so we can

actually go with log and then found

book let's take a look at the console

yep we are good to go now everything is

awesome but let's take a look at the

type we have over here by default it's

actually set to

any which leads to problems because

anywhere whether that is in the loop or

over here I can do something like this I

can set it actually equal to 10 so

typescript is not stopping me and this

is the behavior which I don't want

because I actually want it to be a

string otherwise yeah in here it's going

to be a string if I'm successful inside

of this Loop but then eventually it

might turn into a function again good

old JavaScript variable Behavior but I

don't want this I want this to be a

typescript project where I explicitly

know what is the type so what's the

solution well we can navigate back over

here and and we can set it equal to a

string but now we have another problem

so let me remove these console logs how

do we know that for sure it's going to

be a string because keep in mind this

runs when at runtime so if let's say I

set it equal to

1983 well this Found book is not going

to be equal to a book what is it going

to be equal to well remember by default

variable are what undefined so if you'll

try to set up some kind of logic over

here assuming that it's a string

typescript is going to yell at you it's

going to say Hey listen you are using it

before there's even any kind of value

because again typescript is not going to

check whether at the runtime this will

be equal to a book so yeah we can set up

the logic over here where I can say if

for

sure the Found book is equal to a book

typescript knows that actually these are

strings so we can run the method on it

for example again let's go with length

so this is going to work but we cannot

do it outside of the loop because in

here there's no guarantee that actually

this will be a string so we need to set

up the union type where I'm going to go

with okay it potentially could be a

string but by default actually it is

undefined so it's another type that we

can use so now by default it's going to

be undefined if we're successful it's

going to be equal to a string and what's

super super super awesome is the fact

that typescript is going to be extremely

helpful where if you try to again go

with the good old length notice how it

will immediately add this optional

chaining why well because it can be

undefined and we can see that if we take

a look at the error message if you just

added dot notice Found book possibly can

be undefined and therefore typescript is

going to add that optional chaining so

now we only run this length if it's

actually equal to a string if we have

some kind of value so if we won't be

able to find a book which is the current

case then this actually won't trigger

the runtime error now if we're

successful then we'll be able to nicely

see the length of the book you know what

I will change this one around I'm just

going to go here to Found

book and set it equal to uppercase let

me do it this way so we're going for

uppercase let's invoke that and then

this one I'll just log it again it

really depends whether we're able to

find the book or no so now let me move

this pH book set it up here in my my

console and let's see what is going to

be the result so I'm going to navigate

over here if everything is correct I'm

going to get my four if I'm not

successful then essentially it's just

going to be undefined but I won't have

that runtime error where I'm trying to

access the property on undefined

hopefully that is clear okay and before

we move on to the next topic let's work

on a small Union type challenge where

first we want to create the order status

and in there we'll set up the literal

types and also we want to set up the

discount which can be a number or string

type and you know what just because I

like to break the rules I'm going to

start with the second one doesn't really

matter I'm going to go with number or

string by default I'll set it equal to

20 or any other number value and I also

want to test it whether I can set it

equal to

20% now this works but if I'll try to

set up discount equal to True

essentially a Boolean typescript will

yell at me which is exactly what we

expected and also let's set up that

order status so order status variable by

default is going to be equal to

processing but we want to set up those

literal types so this variable can be

only one of these values so we're going

to start with processing then we'll set

up our pipe and we're going to go with

shipped and also we want to add

delivered over here so now we can go to

the next line set it equal to one of

these ones and everything is going to

work but if I'll try to set it equal to

canceled again typescript will yell at

me so let me just set this one up

quickly where if we go with order status

I just decide that I'm going to pass

this value over here not going to be

successful since I can see this red

squiggly line let me comment this one

out we're done with the challenge and up

next we're going to discuss arrays in

tapescript and as far as the arrays in

typescript the general idea is following

let's say I have prices array and it's

all numbers so we're going to go over

here with 100 75 and then 42 if I want

to set up the type which is something I

want to

do again same deal we go with colon then

we go with type in this case number and

then we set up the square brackets so

now I'm essentially telling typescript

that this array will only have numbers

so if I had a number 34 everything is

fine if file tried to stick hello I'm

going to get the error because this one

is type string and I

explicitly told typescript that this is

actually going to be an array of numbers

and the same is going to work if I will

try to invoke push so if I'll try to add

the item number is fine string will

cause the error so let me comment this

one out the same works with string array

let's say we have

fruit and this is going to be equal to

apple and orange we want to set up the

type over here in this case it's going

to be a string and the same rules apply

if we try to add the item that doesn't

match type we get the red squiggly line

now be careful with the empty square

brackets so if we go here and just come

up with random

values and set it equal to empty square

bracket so if we won't provide the type

over here typ script just assumes that

this will always always be an empty

array so if I set it equal to my array

and start adding items typescript will

immediately complain and notice as we

hover it says well type string is not

assignable to an Mt right so be careful

with this one I know it's temp thing

also be careful when you don't

explicitly set up the type so if I were

to create an empty values

array typescript will get the type but

check it out now the type is any so just

like before we'll run into those issues

because now we can change these values

any way we want so we can take the

string then it turns into a number and

same deal so be careful yes

typescript will infer the type but most

likely you don't want to set it equal to

any so this is the case where we want to

create the MD but we explicitly want to

say yeah this is going to be type number

or string or Boolean or whatever now

also while we're still on a subject of

typescript inferring the type let's take

a look at this example let's say I have

the names array and I have over here

Peter and Susan so if we hover over the

names everything is correct typescript

sees that we have over here a list of

strings and it correctly says the type

for this array is string but here's the

gotcha since typescript is inferring

those values based on what we have over

here in the array it doesn't stop me

from doing this and now if we hover over

it we can see that actually we have this

Union type like I said we'll be coming

back to this topic and now we have

string or number so essentially now I

can add numbers as well therefore be

careful when you're relying 100% on

typescript to set the type it's not

going to stop you from adding different

values to the particular array and in

that case well the type also is going to

change now we can explicitly set up the

array to be one or the other type so I

can go with array for example and I can

say that you know what this array is

going to have either string or a

Boolean again we still set up the square

brackets over here and we set it equal

to an array where we set up those two

values so we can go with Apple

then true which is a Boolean and the

same deal orange and let's set the false

one over here and with this in place we

can start working on our next challenge

okay and once we're familiar with arrays

now let's work on a tiny challenge where

we want to set up the temperatures array

which will be type number and colors

which is going to be type string and

then we also want to set up the mixed

array so let's start with temperatures

essentially our array of numbers now

this one

probably is going to be the hardest as

far as the spelling yep notice over

here me fix that one okay good that took

a while then I want to set up my type

number and we're going to set up 20 then

25 and then 30 and let's try to push I

don't know a string of hot so let's

actually

then go with push and let's try to pass

in the string and we won't be successful

so we can nicely comment this one out

after that we have colors

one so this will be actually type of

string and in here we're going to go

with red green and blue let's save it

and let's try to add a Boolean why not

so colors here dot then push and we're

looking for a bull and mow which is not

allowed and then let's set up the mixed

one so we're going to go with variable

in this case I'm going to call this

mixed array and this one will be either

a number or a string so number pipe and

we set up a string so let's set it equal

to our array and in here you know what

just to make it interesting why don't we

try to add true so bullan and notice

right away I'll have my error so let's

go with one then two and then we want to

add three and with this in place we can

move on to the next topic and up next

let's discuss object in typescript in

order to do that I'm going to create a

car and here I'm going to set up the

brand that one will be equal to a let's

say Toyota and also I'll set up the year

so first let me set up the string over

here and then let's go with year and

we'll set that one equal to a number and

if we want to set up the type annotation

it might look a little funky but we want

to do it this way we again we go with

colon then we go with curly braces and

then one by one we set up those

properties over here so I have a brand

and what is the type well it's going to

be string but also I have a year and

what is that one well that's a number so

again either if I try

to add some

property manually here where I'm setting

up the object or for example if I do it

dynamically by going card Dot and then

the property value unless this property

is in the type annotation it's not going

to work I think I'm just going to use

the color example so let's say I'll set

up the color and it's going to be equal

to Blue notice right away I have the

complaint because the property is not in

my type annotation and the same goes if

I go with car and brand yeah I can set

it equal to Ford since that's the

correct type but again if I go with car

and color it's not going to fly so

typescript will immediately complain now

if you're looking at it and you're

thinking to yourself well boy this is

super clunky over here I have this

object and then actually this is going

to be my type annotation don't worry

this is just essentially the most basic

setup but I wanted to cover it since I

wanted you to understand how everything

works under the hood but eventually we

will cover something called type aliases

where we will nicely be able to set up

this shape somewhere separately and

effectively just reuse the variable so

again you won't have this clunky code

most likely you won't use it but I

definitely wanted you to kind of see

this type of syntax so now once I have

my first car well I can create another

one in this case it's going to be a car

one since I'm already using the car

variable and then I'm going to go with a

different brand and also I'll change the

year and I don't think it's necessary

for me to repeat all of the steps

hopefully it's clear whatever we set up

in this type annotation needs to match

what we have in the object otherwise

typescript is not going to allow us to

compile essentially our code and now

let's tie two things together I want to

tie the arrays with the object and in

the process we'll also cover how we have

read only option with the typescript as

well as the optional properties so first

I want to create three objects I want to

create book pen and notebook and I want

to add them to the items array which by

default is going to be let's say empty

but we'll set up the types in a second

so first let's just go with items not

going to place anything inside of it and

then let's create those three variables

so in here we're looking for a book it's

going to have two things we're going to

go with title we'll set it equal to book

and we'll also have cost okay set it

equal to 20 and then I'll change this

one around to

pen

okay and the cost I mean again totally

relevant I'm going to set it equal to 10

I guess and then I want to go with

notebook but for Notebook actually want

to remove the cost and like I said now I

want to store all of these three values

over here in the items but here's the

kicker though I do want to make sure

that all of them have the same shape now

as we're looking at it we can clearly

see that it's not the case with the

notebook but let's imagine that we don't

know that and at this point we have two

options we can either repeat the same

steps like we did for the car so

effectively I can just set up this type

annotation for all three of them one by

one or since I have an array and I can

also set up the type for array I can do

it in one place where I have the items

so far we know that we can set up the

array to be equal to a string or a

number or a bullion correct and we also

cover the type Union but we can also do

something like this where I can say yeah

this is going to be an array of objects

and then each object needs to have this

particular shape now what is going to be

the shape I'll say title is equal to a

string or I'm sorry I don't know why I'm

placing this in the quotation marks and

then also I want to set up a cost so

we're going to go with cost and we'll

set it equal to a number and now one by

one as I'm adding these items to my

array once I get to a notebook check it

out now typescript is like Hey listen

this notebook that you're adding well

notice it only has the string it doesn't

have the cost so whatever type you set

up over here well it doesn't match so

again super useful where instead of

setting them one by one if we have an

array we can set it in one place because

we also can set up types for array now

what is the solution well technically we

can go back and add cost over here but

we also have this option of adding

optional properties now please keep in

mind you can use the same optional

property over here as well when you're

setting up the type annotation for an

object I'm just doing it here in Array

since this is where we're currently

working hopefully that is clear and now

I don't have the error because when I

set up the cost to be optional well it

could be there or it potentially could

be missing which is the case for a node

and what's also really interesting is

that with typescript we can set up the

properties to be read only again same

deal of course we can set it up over

here but in my case I'm going to do that

for the title where right before I set

up my property I'm going to go with read

only so now if I go with items and I

access let's say the first one here and

if I try to overwrite the value so dot

title is equal to a new book for example

it's not going to fly so now typescript

is immediately complaining that Hey

listen title is readon so you cannot

change this value over here so let me

comment this one out this concludes the

object fundamentals in typescript and

now we can start working on the next

challenge so now let's work on the

objects challenge where we want to set

up the bike we want to set up the laptop

then we'll create some products and

we're going to store it in the array so

let's start with our bike that will be

my object let me come up with some kind

of values over here then we also want to

add the

year and now let's set up our type

annotation so we're going to go with

colon then brand will be equal to string

and also we'll have the here and we'll

set it equal to a number that should do

it now we just want to change it to a

laptop so let me copy this

one change the name then brand stays

year stays we're just going to add a

different string value this case it's

going to be Dell and also change the

year and now let's see some errors so if

I'm going to go with bike and year and

set it equal to Old it's not going to

fly why well because year is set to be

equal to type number and same is going

to work if I'm going to create a second

laptop so I'm going to go with laptop 2

and it's only going to have a brand so

we're not going to have the year so if

I'm going to set it like this notice we

get our red squiggly which means that

there's some kind of error and now let's

set up those products so we're going to

go with product one that one is equal to

title let's go with

shirt and let's set up the

price that one will be equal to

820 then let's copy and paste we're

going to go with two this one will be

equal to a pants one why not pants are

awesome now we don't want the price so

we will need to set this one up as

optional and let's create the product

all right let's right away set up our

type by the way this was supposed to be

square brackets we want to go here with

title that one is equal to a string and

then also we want to go with price this

one will be optional and we'll set it

equal to a number so now in the array we

can nicely store product one and product

number two now it looks like typescript

is complaining why well because I forgot

the square brackets and at the very end

let me just showcase something

interesting where if I go with products

and then push

provide the object set up a title here

in my case I'm going to go with shes

even though price is optional we still

need to provide the correct type so

let's say if I don't provide anything

notice how typescript is not complaining

effectively this is optional

the price one now if I do provide the

price it has to be a number so if I go

here with price and set it equal to a

string T will immediately complain yes

it's optional but if I do decide to pass

the value the type needs to match

whatever I have here in the type

annotation beautiful we have finally

arrived at the functions in typescript

and I'm super excited to cover this

topic for a few reasons first our

examples are going to get more complex

because we'll start tying together all

of the concepts we covered previously

and also once we start working with

functions we absolutely have to start

using typescript and you'll see what I

mean in a second so let's say I have a

function of say hi why not let's set it

up say hi for now we're not going to

pass any parameters and as far as the

function logic we'll just leave it empty

now say high is looking for what well

probably some kind of name correct and

in a function body we can nicely log it

so the moment I type over here any

parameter in my case name notice right

away I'm getting these red squidly lines

and this is what I'm talking about at

this point we absolutely have to start

using typescript otherwise typescript

won't compile our code so if we hover

over we notice parameter name implicitly

has any type and essentially typescript

complains about it so that's not allowed

yes by default implicitly it's a set up

as any but we need to fix it in order

for typescript to compile our code and

at this point essentially we have three

options first we could set typ any

ourselves elves that's definitely one

option also and you know what let me

just comment this one out also we can

navigate to DS config and we can

actually change the configuration

something I'm going to Showcase in a

second or the best scenario is for us to

actually set this one up with a proper

type annotation so in this case I'm

looking for a string most likely so I'm

I'm going to say type okay so let's try

it out here with any what's the issue

here well just like we covered before

any is anything so everything that we

can do in JavaScript pretty much will be

able to do with the name here and

actually I believe in two videos I'll

showcase the any GOA that we need to be

aware of so this is not going to be

approach yes technically you can do it

but I mean at at this point we kind of

lose the benefits of typescript now

second option we can navigate over here

to the package Json or I'm sorry why am

I going to package Json we're going to

DS config and notice over here this

strict rule technically we can change it

around I can set it equal to false and

at that point typescript won't complain

about the fact that parameter by default

is left as any so you can definitely try

it out you can set it equal TOA and

you'll see that actually code Works

everything's fine but in my case I'm

going to skip that I'm just letting you

know that technically this is an option

so we have finally arrived at the option

we're going to use and that is setting

name explicitly to the type we're going

to use and just like before we simply

want to go with colon and we want to

come up with the type my case that is

going to be string and again I know

you're probably sick of this method but

I'm just going to use two uppercase

essentially I want to set up over here a

log then I'm going to go with template

string and we're going to go with hello

there over here and now I'm going to

access the name so the moment here we

set up a proper type let's say string

number or whatever two things are going

to happen first when we call this

function every time we'll pass in a

wrong type typescript is going to yell

at us and second within this function

body we can only perform functionality

that is allowed on this specific type so

in here yes let's go to uppercase let's

invoke it and let's try invoking say hi

and let's say I'm going to pass in John

and also in the next line I'm going to

pass in three so if everything is

correct we should get an error over here

we can nicely see that we can only grab

the string Methods inside of the

function body and if we inspect the

console we should see John over there

and lastly if we try to pass more

parameters than what we have specified

we'll also get an error and typescript

won't compile our code and with this in

place now we can move on to the next

topic okay and up next let's talk about

function returns so first I'm going to

create a function and I'm going to call

this

calculate

discount discount over here it's going

to be looking for price and I know that

that type is going to be number for now

inside of the function body I simply

want to go with the return and we're

going to go with price again since this

is a number once I press do notice I'm

only getting the methods that are

associated with the type number and if

you're sick of me hearing this I'm sorry

but I'm going to keep on repeating that

because again I find this truly helpful

and let's say I'm going to multiply this

by

0.9 so I'm going to go over here 0.9

okay good and then I'm going to set up a

variable so I'm going to go with cons

final price and I'm going to set it

equal to calculate discount I'm going to

pass in 200 and I don't think I need to

log the value I I don't think it's

necessary so if I hover over the final

price I can see that it's a number now

why is that a case because again

typescript is inferring the type

typescript says okay so this is a number

here we're returning a number multiplied

by something so whenever we hover over

this calculate discount we can nicely

see another set of colon and a number

over there and I know that it might look

a little funky over here but yes

essentially the syntax is following in

order for us to set up the type for the

function return we need to go after

parenthesis we need to set up the colon

and then we explicitly need to go with

the type now again you can make a case

well why do we need to set up type if

typescript is already inferring the type

well for essentially two reasons first

of all if I set up over here a number

type explicitly as I'm working in this

function if for some reason I forget to

set up the return or if I set up a

return which doesn't match what

typescript is expecting well I'm going

to get an error so it's going to be

super helpful let's Imagine This I have

some kind of has discount variable over

here and I'm going to just set up has

discount so essentially some kind of

condition and in here instead of

returning a number I'm going to go with

discount and applied notice right away

typescript is complaining type string is

not assignable to type number as we're

working in the function typescript is

kind of watching over us and if I return

something that I'm not expecting well

essentially typescript just starts

yelling at me because again yeah it's

trying to infer the type but once I

remove my logic well essentially now it

could be a string or it could be also a

number correct so now if we hover over

this notice we either have a number or

it's going to be discount applied and

the same goes over here either it

returns a number or discount applied so

even though it's technically optional

it's a good practice to set up the

return types explicitly since it helps

us tremendously as we're setting up the

functionality so now let me common this

one out and I'm just going to go with

price like so and with this in place now

we can move on to the next topic and

next I just want to show you why we want

to be careful with type any but this is

one of those videos where you don't have

to type along if you're not interested

essentially you can just sit back and

relax so let's imagine I have a function

and the name is add three so it's

looking for one parameter which is a

number and don't ask me why but I'm just

going to set it equal to any so I'm not

sure what would be the use case but

let's just go with it then inside of the

function body I'm going to create

another number in this case type will be

a number so I'm going to be explicit and

then as far as the return let's just go

with a return number plus another number

why not and then let's set up two

variables one is going to be result and

then we'll also set up some value so

let's try it out I'm going to go over

here with result that one is equal to

add three so as far as the value you

know what let me just pass in three so 3

+ 3 and then also we want to set up some

value so that one will be equal to a

result so now M Dar question and now I'm

not asking what is going to be the

result I'm more interested well what is

going to be the type so if we have our

over some value notice something

interesting

how essentially it's any and what that

means well go with some value and my

method and technically it's going to be

valid as I'm typing the code

but hopefully it's clear that it will

lead to some errors since there is no

method My Method and as you can see

everything starts with this innocent any

and notice how it trickles down so we

pass number that is type any and even

though this is a number and technically

this is a math operation typescript

should infer that we're returning a

number however if we hover over notice

over here we're expecting any we are

returning any so result is any then Su

value is any and as I mentioned before

be careful when you introduce any

because it can slowly trickle down or

spread like wildfire whichever term you

want to use and next thing you know it

you're going to be unintentionally or

intentionally running some methods or

setting up some kind of functionality

which doesn't make sense and at that

point you'll again need to start chasing

those bugs at runtime not as you're

writing the application so now if I

navigate to the browser notice over here

some value that my method is not a

function an error which which we can

expect since there is no such method on

some value and with this in place now we

can work on our next challenge beautiful

and once we're familiar with the

fundamentals let's work on our next

challenge and you know what I actually

changed my mind I will list out the

steps for a few reasons first the

challenges are getting more complex and

also I want everyone to be on the same

page let's say someone one is not

reading the readme or utilizing the

readme I still want them to kind of have

an idea what I'm trying to build so

effectively I want to create the array

names and then I want to write a

function that checks the name whether

it's in the array so this function

should take name as parameter and it

should return a Boolean whether the name

is in the array or not and then we want

to set up one or few checks and

essentially just test out some names so

let me go to my file first I want to

come up with a value and I'm going to

say that it's going to be an array of

strings and let's just provide some

random values so I'm going to go here

with John then I also want to go with

Jane let's set up Chim and also will

place a gill over there I don't know why

I said all of them starting with J must

have been a bad day in the office or

something like that then let's come up

with our function so in my case I'm

going to go with is name in list and

this function is going to be looking for

a parameter the type is going to be

string and I'll right away set up that I

want to return from this function a

Boolean so what

the name is in the array or not

therefore I'm going to set up my type

over here and then right away let's set

up the return I'm going to go with names

so that's the array and I'm just going

to use the includes method and in here

I'll pass in the name so I pass the

string over here and then I pass the

same one into includes and essentially

this is just going to return true or

false then let me set up a variable name

to check now technically I mean we don't

have to do it we can just pass it in but

you know what just to make things more

interesting I'm going to go with name to

check um in this case you know what I

will rely on the fact

that typescript will infer this type let

me type over here Jane and let me set up

if and else so I'm going to go with his

name in a list and I'm going to pass in

name to check that's the case I'll have

one log if not I'll have something else

so now let's set up those logs so in

here we're looking for a name to check

whatever it might be so now let me

access this as a variable so name to

check and then let's say in the list and

now pretty much let me just take the

same console

log and and add not in

list okay good and now let me save the

file let me navigate to the browser and

if everything is correct Jane is in the

list so if I'm going to set it up over

here a value of Peter now it's going to

say Peter is not on the list and with

this in place we're done with the

challenge and we're ready to move on to

our next topic and next let's discuss

optional and default parameters in

functions

essentially how we set them up from the

typescript

perspective I'm going to start by

creating a function

calculate

price it's going to look for two

variables price which is going to be

number and for now I'll set

discount as a normal parameter so I'm

not going to set it as default or

optional so let me go with discount let

me set it up as number then inside of

the function body I'm going to go with

return and we're going to look for Price

minus the discount okay good makes sense

I mean if we want we can set up over

here a number as a return as well that's

definitely an option and then let's go

with price after

discount and now will be equal to

calculate price and I'm going to pass in

some even numbers just so we don't need

to log it so essentially I pass in

100 as a price and20 as a discount and

then the result should be 80 all right

but what if I want to make this one

optional what if sometimes I'm going to

provide the value and sometimes well

it's not going to be available well the

syex is following we want to go to the

parameter and we need to add the

question mark but notice right away

typescript is

complaining and the reason for that is

because possibly discount can be

undefined and in our case we already

have a math operation where we take the

price and then we subtract a discount

but if this is undefined I mean it

doesn't make sense so the key thing to

remember about optional parameters is

that a function with optional parameters

must work when they're not supplied and

as far as the effects well we just need

to provide the fallback value so if this

is undefined the discount one well then

we'll have some kind of number value and

the way we do that we just set up the or

operator and in this case I'm going to

go with zero that's how we can work with

optional parameters in typescript and

while we're still on a topic let's also

discuss the default parameter now for

this one I think I'm going to create

another function why not let's just keep

on practicing this one is not going to

be calculate the price though we're

going to go with calculate score we're

going to pass in the initial score which

will be a number and also we're going to

go with penalty points and same deal for

now we're just going to set it that it's

actually a number I mean it will be a

number but we'll just set it as a

default eventually now as far as the

return again same deal we're going to

set it equal to a number and when it

comes to logic we want to go with return

initial score minus the penalty points

and once I have the function in place

now let me set up two variables so we're

looking for

score after penalty and I'll provide

over here calculate score and again I'm

going to go with with some even values

so I'm going to go with 12 and now I

want to set up another variable only in

this case I'm going to go with without

penalty and I'll just provide the first

one so that will be my initial score and

notice right away typescript is going to

complain so here's the deal if we set up

a parameter and we don't provide it or

we provide one too many

well then typescript will complain so

this is something to keep in mind and

how we can fix it well we can either go

back to this optional parameter which we

discussed in the previous video or we

provide some default for this one so we

make penalty points as a default

parameter and the way we do that just

like with JavaScript we just add the

equal sign over here and come up with

the value so in my case it's going to be

zero so now

if it's provided awesome we're going to

use the penalty points value if not well

then we'll just revert back to the zero

because that one is the default one and

here's the key difference if we use

optional parameter we do need to set up

this logic if we have a default one it's

not the case then we'll just use

whatever value is provided okay and up

next let's discuss how we can work with

rest parameters

in typescript and also let me showcase

one more time how smart the typescript

is let's say we have a function and the

name is going to be sum now for now I'm

not going to pass any parameters I'm not

going to set up any return type simply

want to have my function and I'm just

going to invoke it and show you what

arguments I'm going to provide so this

one will be equal to result and in here

I just invoke the sum and effectively in

here I want to provide two arguments so

I want to provide a string and a list of

numbers so string is going to say well

the total is and then whatever numbers I

provide they're going to be added

together and that will be my sum so in

here let me go with the string and let's

say

total is

then we're going to go with the colon

and then we have list of parameters so

this is where we'll need to implement

the rest parameter otherwise I mean one

case I might add five numbers in the

next instance it might be only three and

hopefully you see where I'm going with

this so it's not always going to be one

or two numbers it's going to be a list

of numbers so in this case I'm going to

go with one 2 3 four and five now

typescript is complaining since we

haven't set up those parameters over

here so let's start with a message in

this case it's going to be a string and

now let's see how it can work with such

list and essentially the syntax is

similar to JavaScript the only

difference is that we need to provide

well what type of array it's going to be

so in JavaScript we use this syntax

three dots then we come up with a name

in this case I'm going to go with

numbers over here and this is the rest

parameter and essentially JavaScript

treats this as an array so in here we

want to go with number because I need to

let typescript know what kind of type it

is and then the array now please keep in

mind if you have strings here as well

essentially you just go with number then

use the type Union and essentially set

up a string there as well and now pretty

much all of the arguments that are pass

the string are going to be collected in

this numbers array now I also right away

want to set up what are we returning

from this function and essentially it's

going to be a string now before we set

up the logic which we're going to do

with reduce I also want to showcase how

smart typescript is so I'm just going to

create

the doubled variable and I'm going to

set it equal to numbers so that's my

array then let's invoke map then we're

going to go with

num and let's just return num * 2 and

again let me just log I guess here just

so we can see that the functionality

works but one I want to showcase though

is this notice as we hover over

typescript immediately knows that it's a

number so let's say you have some kind

of call back function that you pass into

the map into the reduce and all that

that's is going to see what kind of type

array it is if you have supplied those

values and it will immediately know that

as we're iterating over this is a number

now you can explicitly provide the value

I mean no one is stopping you to go here

and say number but in general typescript

is super helpful and we also have right

away this useful error where the type

should be string as far as my return but

at the moment well I'm not returning

anything so let me set up that

functionality as well and this is the

case where I will use the reduce and

then I'm just going to return the

message the total is and then I'll sum

up the values so I'm going to go with

let total is equal two numbers then

let's provide reduce over here I mean we

can call this accumulator and total or

current however you want to do it in my

case I think I'm going to go with

previous over here and the current

one and then as far as the

logic side of the function let's just

return previous plus and then the

current one and the same deal typ knows

that it's a number since I have array of

numbers now since I'm using reduce I

also want to provide the default value

which is going to be null and then from

this function I want to return a string

so I'm going to set up the template

literal we'll provide the message and

we'll also provide the total over here

so now let me just see what the result

is I guess so let me just log the result

and also we should see that doubled one

in console so notice this functionality

works over here and the total is 15 and

in the process we cover two important

things how we can work with rest

parameter which essentially collects the

list of values if we don't want to

access them one by one and also how

smart typescript is in the Callback

function we don't need to explicitly say

well what type it's going to be

typescript already knows and up next

let's discuss what type we should return

if we're not returning anything from the

function and a good old example is just

having a console log so let me go with

function log message as far as the

parameter we're looking for a

message and that one will be equal to a

string and then in here let's use our

good old console log and let's just log

the message now I do want to invoke it

and I want to provide some kind of value

so in this case I'm going to go with

hello and typescript and since we have

nice suggestions if we just hover over

the log message we can see that

typescript inferred the return type as

void and void is a special type that

represents the absence of a value and

when we use it has a function return

type void indicates that the function

does not return a value now milon dollar

question do you always have to set it up

I mean it really depends on your

approach but it is super helpful

especially if you consider this once we

add this void over here even if I set up

some kind of return and I'm going to go

with hello world notice how typescript

right away says well you cannot assign

string to a void so if we decide that

this function is not going to return

anything and we set up the keyword even

if later on we mess up something and

start returning some values from the

function typescript is going to stop us

from doing that and up next let's

discuss Union types as function

parameters and what the typ guards are

now I did set up this topic as a

challenge just so you can see firsthand

the type of issues we will face so

here's the task I want you to create a

function called process input that

accepts a parameter of Union type so it

can either be a string or a number and

when it comes to

functionality if the input type is

number we simply want to multiply it and

log it in the console and if it's going

to be a string just use one of the

methods so in my case since my favorite

method is the uppercase one most likely

I'll use that one but it really comes

down to the preference so I'm going to

navigate to my tutorial and I want to

come up with a function so I'm going to

go with process and then input and I

believe in one of the previous videos

when we covered the rest parameter I

mentioned that you can still use the

union type I mean it's not a big deal

here I can go with input and then just

say string or the

number however once we set up the

functionality this is where we'll add

additional logic since now we have two

potential values correct so first let's

go with process input and pass in then

this should work and also let's pass in

the hello now what about the logic if we

simply log we should be good to go so if

I type input notice there are no issues

but now what if I want to multiply this

what if I want to say times two notice

immediately typescript is not happy why

well we have a type

string and we're multiplying this by two

now typescript doesn't know that in here

we passing in 10 and in here we have the

hello so we need to set up something

called type guard where before we do any

functionality we actually make sure that

the type is correct essentially if I

want to run a string method I want to

make sure that it's a string if I want

to multiply I want to make sure that

it's a number and again the fancy name

for that is typ guard now we you'll look

at multiple type guards the most

straightforward one is just type off

keyword and then we look for specific

value so inside of the function I do

want to set up a check so there's going

to be a condition and I'm going to go

with type off then I'm looking for my

parameter and I'm going to say if it's

equal to a number and notice how

immediately typescript was helpful and

provided bunch of options if you didn't

let me go back notice these are the

values that we can use and in this case

we're looking for the number if that's

the case what do I want to do well I'm

going to log times two over here now if

it's not the case typescript is also

smart it knows that listen if it's a

number we're going to do this

functionality what is the alternative

well the alternative it's a string

correct so in here we simply can go with

else then again we're going to go with

log

input and you know what just so people

are not upset with me I'm just going to

go with two

lowercase again the official name for

this one is type guard and we use it to

check the parameter at the runtime and

while we're still on a roll let's also

see how we can work with objects

as parameters in our function so I'm

going to set up a new function let me

call this

employ and in here I'll pass in the

object with the ID property and as a

side

note the second example which we're

going to cover is going to use a little

different syntax so in here essentially

I'm right away D structuring the ID I'm

saying yeah there's going to be an

object with the ID property and I right

away want to access it now as far as the

typescript same deal just like with

regular objects we want to set up this

type annotation and we want to be

specific well what are we're going to be

getting here so is this a number string

or whatever and in this case I'm going

to set it equal to a number as a side

note yes in like I believe three videos

we will cover typee aliases so it's not

going to be as clunky because at the

moment I fully understand if you're

looking at it and you're like whoa so I

understand this part but does that mean

that every time I'll have object with

like 10 properties we have to set it up

over here no there is a better solution

and it's coming up and also just like

with parameters can also set up the

return type as an object out of does

that look like well same deal I just say

colon then I provide the curries and

what are we returning from this function

I'm going to go with ID which again is

going to be a number and also there's

going to be is active in this object and

that one will be a Boolean and again we

set up the

Cur so we have two sets of curries over

here and we also have two sets over here

because we have one for return and one

for

functionality and as far as the logic I

just want to return an object from this

function and I need to make sure I

follow this pattern correct I need to

make sure that I return a number and a

Boolean so in this case I'll just right

away grab whatever I have over here and

also as far as the is active I'm just

going to do some basic logic I'm going

to say ID and then I'm going to use the

modulus operator essentially if ID

modulus 2 is equal to zero then it's

going to be true which means essentially

that it's an even number if not then

it's going to be false so now let's try

it out we're going to go with const

first set it equal to create employee

and then let's pass in our object so in

this case it's going to be one then copy

and paste this will be equal to a second

over here and then we want to log both

of these results so let's look for first

and second let me navigate to a console

and for some

reason says false because yep I didn't

change this one this should be equal to

two so now the first one is active is

false and then the second one is active

is true again we really don't care about

the functionality I mean we can

definitely hardcode over here doesn't

really matter so hopefully it's clear if

we have an object we nicely set up right

away The annotation at least with the

current knowledge we have now also we

have alternative approach where we can

give some kind of name to this object

and then we can just use it inside of

the function body again please keep in

mind the general idea as far as

typescript doesn't change but I do want

to make sure that we understand that we

have multiple approaches so let me call

this

alternative over here then we will go

with function create student in this

case and I know that I'm going to get

the

object and I'm just going to give it a

name of student so this still will be

object but I'll just access it with

student. student do and same deal I want

to go with my annotation I'll say that

ID will be number and name will be equal

to a string over here and and then as

far as D function body I'm actually

going to go with void so we're not going

to return anything from this function

and we're just going to log stuff so let

me scroll down a little bit let's set up

the template literal welcome to the

course I

guess and let's access the student where

we go with student and notice we right

away get the suggestion which properties

are on this object since this is what we

specified

in our type annotation and in this case

I want to go with name and then to

uppercase also please keep in mind that

yes we can the structure right here in a

function body as well that's totally an

option so now let me call

it with the new student so in this case

just to again showcase that we have

multiple approaches we want to go with

student we want to set it equal to an

object I'm going to go with five over

here and name is going to be Anna and

I'm just going to rely on typescript to

infer the type and then we'll go with

create student pass in the new student

and if everything is correct we should

have the value in the console and with

this in place we can move on to the next

topic okay and before we move on and

start working on our next challenge

let's also cover the access property

check gotcha and for this one actually

we don't need to create too much code

from the scratch I'm just going to

remove my first function from the

previous video I'll leave create student

as it is and I simply want to invoke it

right

below and in this case I will pass

everything in line so unlike previously

where we set the object now I'll provide

all of these properties one by one let's

start over here with ID I'll set it

equal to one as note it's totally

irrelevant to what we pass in here

that's not the gotcha the gotcha is

following if we add here extra property

what do you think is going to happen

well we have a type annotation for ID in

string correct so I mean logic tells us

that if we add here email and we set it

equal to Bobo at gmail.com typescript is

going to complain and you're totally

correct essentially it says Hey listen

you didn't specify that there's going to

be an email while you're adding this to

the object so this is something we

expect however notice this interesting

Behavior where I can go here with an

email

and essentially pass in some kind of

value and you know what it's going to

work typescript is not going to complain

so yeah this is this interesting

Behavior

where when we pass in object properties

in line typescript expects to match this

exactly so if we'll add some extra

properties TPT will immediately complain

because in typescript mind we have a

full control of what we're adding in

line however if we're just referencing

the object and there's an extra property

the only thing typescript cares about

are the properties that are in the type

notation so if there's 120 extra

properties typescript is like okay do

you have an ID and name if yes we're

good to go if not then of course there's

still going to be an issue hopefully

it's clear just remember this gotcha and

you'll be good to go all right I think

we're ready for our next challenge and

at least in my opinion this one is going

to be super interesting because we'll

combine multiple things from the

previous videos so we want to create a

process data function which is going to

accept two parameters first one is going

to be input parameter which can be a

string or a number and second one will

be a config object and instead of that

config object we'll have the reverse

property which is a Boolean so if we

pass in a number we just want to

multiply the number with its own value

essentially input multiplied by the

input however if the input is the string

our second option and if the reverse is

true we want to reverse the string

and set it uppercase now if we provide a

string but the reverse is set to false

well in that case we'll simply set up

the string to be uppercase and just

return it so let me navigate to my

tutorial I think I'll just remove all of

this logic and you know what for stars I

want to set up a

function in here I'm going to call the

this

process data I'm not going to set up any

parameters yet same goes for

functionality and I simply want to log

it in three places essentially invoke it

and then log it so in the first case I'm

going to pass in 10 and

then I'll set up two more hellos so

these are going to be instances where we

pass in the string and now as far as the

process data like I said we have input

over here but we want to use the type

Union so either it's going to be a

string or it will be a number so that

will be our first parameter now the

second one is the config one if we pass

this config in there there's going to be

a reverse property and as a sign note I

actually forgot to do that so first one

is hello and then we want to go with our

config

object and I will set the reverse equals

to true so let's navigate to our

parameters and let's set up the second

one so I'm going to call this config

it's an object and in there I'll have

the reverse property so I'll set it

equal to a Boolean now here's the kicker

what if I pass in the number do I really

care about that reverse one

and the answer is no I only care about

it if it's a string correct only then

we'll check but if it's a number I mean

doesn't really matter and therefore I

can nicely set this as default reverse

false so I'm not going to have to do

that additional check basically Once I

pass in the number I don't have to pass

this additional config object so in here

let's go with default one and set it

equal to verse and false now let's also

set up what we're returning from this

function so either it's going to be a

string or a number and now when it comes

to logic well we have two options

correct so we can have a string or a

number so we do need to set up a typ

guard if we want to multiply it I want

to make sure that it's actually a number

so let's go with if then type off if the

input is equal to a number well that's

when we want to multiply and return so

let's go with return that input times

input and it looks like I have a tiny

typ over here this should be return and

also we want to set up the else and in

here we're going to go with the return

then we'll check the config reverse so

by default it's going to be false so if

it's true then we want to set it to

uppercase split reverse and join if not

well then we'll simply return it with

the uppercase so let's set up over here

a dinary operator we're going to go with

input then to uppercase let's invoke

that then we're going to split it then

we'll call a reverse on

it over here and then lastly let's use

join method let's do this and if it's

false which is the default one we're

going to go with input then

two uppercase and we're going to invoke

it so now let me navigate to the browser

and let's see so I have 100 then I have

straight up hello just to uppercase and

then I have the reverse value again in

my opinion the biggest gotcha is over

here you see if you're not going to

provide this default value over here

then pretty much every time you'll

invoke this processed

data it's also expecting this object

over here and if that's the

functionality you want to go for it's

definitely an option but in my opinion

it's super useful to add this default

one because in that case well if it's a

number or if I don't want to actually

reverse it well I simply don't provide

that argument at least that was my line

magic and with this in place we're done

with the challenge and we can move on to

the next topic all right and we have

finally arrived at the type alas at

least in my opinion one of the most

exciting topics because once I learned

the topic I was super super excited

since it just eliminated bunch of clunky

code and for this one actually want to

start with the code

already present because I want to cover

some stuff on I highly encourage you to

do pretty much the same there's really

no need to type this from the scratch so

grab it from the readme and then let's

go line by line so we have two objects

and we nicely set up over here the type

annotations where ID is a number name is

a string and is active is a buan so if

I'm setting up some wrong values

typescript is going to be super helpful

and then we have a function which again

is looking for a user and that user must

have this particular shape ID is a

number name is a string and is active is

a buing okay beautiful and not only that

but from this function for some weird

reason we return the same thing we

return the same shape we return ID name

and is active and so is the

functionality we just set it to

uppercase and then return the user and I

can tell you right away that there's

nothing wrong with this code as far as

functionality all of this works what is

the biggest issue I mean we have code

over here same code over here same code

over here and then we have the return

and this is just one file what do we

have like 20 lines of code and pretty

much we just

constantly keep repeating this so

without further Ado I want to introduce

you to a type areas in typescript which

again in my opinion is extremely helpful

feature now before we continue let me

just make sure that we are all on the

same page you see a type Alias is just a

new name or a shorthand for existing

type and in this case we're talking

about this type over here this type

annotation so nothing is actually going

to change as far as this syntax is

concerned however with type Alias it's

going to be easier to reuse this one so

again please keep in mind we're not

creating a new type it's just an Alas

and all of the same rules apply to the

alas one that's why I

wanted initially to cover how we set up

such inline type annotation because

nothing is going to change as far as our

functionality including the optional

property and read only modifier the only

difference well now the code is going to

be in one place so if we ever want to

change something we will only need to do

that in one specific place and also our

code is going to be less clunky because

we'll just use that name and once I'm

done with my long and B Bing monologue

why don't we set it up and essentially

the syntax is following we want to go

with type that's the keyword now the

convention is to go with the uppercase

but you don't have to I mean you can

call this also like this but in my case

I will go with user and like I said

before the syntax is the same so I

simply want to take my first instance

and set it equal to my user so now all

throughout

my file document project whatever I can

use this user and this will mean the

same exact thing so in here I can go

with yeah John is going to be object and

a type is actually going to be user same

is going to be over here Susan is going

to be a user now when we're creating a

user what is the type well it's a user

type and you can probably already guess

same is going to be over here so we can

go with user and now me question which

one is easier to manage and

read and if you said the second one

you're absolutely correct so I can mess

with you and say that you know what no

actually this one was easier to work

with but in reality we can clearly see

that this is definitely easier to work

with and I'm skipping a little bit ahead

but we can actually also export this one

as well as well so it's definitely an

option so let's say we set it up in one

file and then if we ever want to use

this type alas somewhere else we can

nicely export it import it in the file

and we're pretty much good to go okay um

before we move on and start working on

our next challenge I also want to

quickly showcase that we're not limited

to using type Alias for object so it's

definitely an option it's definitely

something thing we're going to do but

you can also do it for our previous

examples as well for example I can go

here with type I'm going to call this

string or number and I'll set it equal

to string then use the union type and

set it equal to a number so now anywhere

in my project where I want to use the

union string or number I can use my type

Alias instead of this hardcoded value so

let's say that there's a value this one

will have a type string or number and

then we can go with value hello and also

we can set the value equal to 1 two 3

now is this something you're going to

see

often uh most likely not but still I

definitely want to make sure that you

know that it is a possibility now

something that you will see quite often

at least in my code is this I'm going to

set up an alas but in this case I'm

doing that for the literal type so I'm

going to go with light or dark so this

will be my tee and those are the values

so it can be only light or dark and now

if I have a theme

variable I can go type theme then let me

just change the values here notice how I

right away have only these two options

something I have discussed already quite

a few times

and in this case I'm going to go with

light and what's also super super

awesome that I can use the same theme

one in the function so if I go here with

set

theme it's going to be looking for a

parameter by the name of T and the type

over here is actually going to be a

theme and now I want to set my theme

variable equal to

whatever parameter gets passed in so now

when we invoke the theme same deal over

here notice how we can only use these

two values again super super helpful

especially as your project grows bigger

so we can nicely set up this Alias and

then use it when we set up the property

or when we pass some parameter in the

function and up next let's work on

another challenge and and during the

challenge we'll cover a few interesting

things we'll cover how we can set up

type Alias with the array how we can set

up type alas with type Union and how to

set up a typ guard if we're working with

the object so here's the challenge we

want to set up two types one is going to

be the employee type and second one will

be a manager type now for employee

will'll set up two instances and then I

guess manager will set up only one now

the key difference is that for a manager

there's going to be employees property

and it's actually going to be an array

of employee types so this is where we'll

combine the Alias with the array and

then we want to set up a function which

actually is going to accept both types

whether that is the employee or the

manager

and if the instance is the manager then

we just want to showcase how many

employees they have and if it's not the

case then we'll just log in which

department the employee is working so

let's try to set this one

up I'm going to go with my alas first

and I'm looking for

employee so this one will set it equal

to an object there's going to be an ID

property which is a number then we'll go

with name we'll set that one equal to a

string and then also there's going to be

a department and for some

reason I have a hinch that this is not

correct typing so let me fix that so

we're looking over here for Department

which is a string

now there's also going to be an alias

for

manager for this one same deal ID number

name String so let me just copy them in

order to make it faster and now I want

to set up the

employees which is going to be an array

but an array of what it's not going to

be an array of strings or numbers and if

you remember in one of the previous

examples we actually covered that we can

set up type to be an object only in this

case we already have the type Alias for

that so I can simply say yeah it's going

to be an array but it's going to be an

array of employees okay good now let's

set up those instances and then we'll

work on a function so for starters

there's going to be first employee we'll

right away set up the type just so we

don't mess up anything

ed1 then

name let's set it up and also let's come

up with the department and in my case

I'm going to go with sales let me copy

and paste now I want to change the

variable name so in here we'll set up as

Steve same deal over here and then as

far as the department let's go with HR

then let's set up our manager as well so

this will be Bob the type will be

manager ID one name Bob or Bobo even

better and then we'll go with employees

and this is our array correct so now I

want to grab Alice and deep so let's set

these two up and now let's invoke the

function the print staff details but of

course before I can invoke

it it would be useful if we would have

this function in the first place correct

so let me come up with the function I'm

going to call this print staff and then

details but here's the kicker how are we

going to pass this in because at the

moment we have two

types so are we going to pass in just

employee and then set up another

function for the manager or we can

somehow some way combine the two and the

answer is well we can use the type Union

so essentially I can go with type and

then staff and set it equal to employee

or it's going to be a manager and now

this is our type so now I can nicely go

to print staff detail details and say

okay there's going to be an object and

as far as the type actually going to be

equal to a stat now I do want to set up

the void over here since we're not going

to return anything and now another

million doll question well how we can

check whether the staff object is the

employee or a

manager because if it's a manager then

we do have an array but if it's the

employee that's not the case and we

cannot go with well is type off equal to

an object well both of them are equal to

an object so that's not going to make

much difference here's what we want to

do so we want to go with our condition

and then we need to pick a property

which is specific to the object so in

this case that's the employees correct

so we go here with the property and we

say in and then our object over here so

that's the staff if it's the case well

then we know that it's a manager if not

then we know it's a staff one so let's

go and log something here we're going to

go with staff name so let me access this

one

staff name and then we'll say is an

employee in the specific department so

in here we want to access again the

staff one and now we're looking for

Department again a property which is not

on a manager and again typescript is

smart it knows that if there's an

employees this is going to be a manager

if not well that's the staff then and I

can access the department so let me add

this one and now I want to just grab

this console log and we'll just change a

few things around still going to be a

console log but we're going to go with

manager and notice how right away

typescript is correcting us essentially

it says well department does not exist

on type manager so now what do we want

to do well we'll remove this we're going

to go with employees and we're looking

for length and let's just type

employees okay good let's try it out

going to navigate to the bottom and

we're going to go with print staff

details let's pass in the first one and

and let's also pass in the Bob once we

navigate to the browser we see that

Alice is the employee and Bob is the

manager so this is how we can combine

multiple features this is how we can set

up type Alias with the type Union this

is how we can start using type aliases

with the array and this is how we can

set up a typ guard if we are working

with the object uh next let's discuss

the intersection type in Union which is

a way for us to combine multiple types

into one let's imagine this scenario we

have a type book it is equal to a number

name is equal to a string and there's

also a price so we set up this number

over here and we're good to go then

let's create let's say two instances I'm

going to call this book one is equal to

an object and let's right away set up

our type our book type and then in here

let's provide some dummy values ID will

be equal to one name will be how to cook

a dragon because why not and also let's

set up some kind of price so in this

case it's going to be some random

15 then let me copy and

paste and instead of Po one this is

going to be b 2 now the type will stay

the same the ID will be two as far as

the name we're going to go with the

secret life of unicorns and we're going

to set the price equal to

18 so all this is good but what if I

have a discounted book where not only I

have these three properties but there's

also a discount so first let's set it up

and you know what I think we can speed

this up a little bit where it's not

going to be a book we're going to go

with

discounted book okay good now for now

type will be book but clearly we'll have

some issues I can right away tell you

that then let's come up with the name in

my case I'm going to go with this one

price will be equal to 25 and we also

want to add this discount property and

we'll set this one equal to

0.15 and notice the moment we do that

typescript complains why well because

it's not in our types so there is no

discon anywhere here so what's the

solution well we could create another

type correct we could just copy and

paste and set up over here a discounted

book type and then just add that

discount property it's definitely an

option or we can nicely utilize the

intersection type how's that going to

look like well we have multiple ways how

we can set this up you can definitely do

it over here in line where you go with

and operator and you just add what more

types you want to have for this

particular instance so in this case I

can go with discount and I can set it

equal to a number and notice typescript

doesn't complain anymore so now

essentially it uses all of the

properties from the book type already

but we just added nicely the discount as

well so that's one option or we can set

up another alas now the logic here is

not going to change so I can just cut it

out and go type then discounted book and

we're going to set it equal to this one

so now for my discounted book I can use

the discounted book type Alas and again

the difference with Union type it's

either going to be this type or the type

on the other side of the pipe however

with the intersection type now we

combine them now we say yeah it's going

to have all of the properties that we

have in the book type and also there's

going to be this discount one which is a

type number all right and at the end of

the type Alias section I quickly want to

mention that type Alias also supports

computed properties so we we don't

always have to hardore code for example

if I have a tiger object and eventually

I'll set up the type you know what for

now let's just set up the object in here

I can go with age and set it equal to

five so nothing new but we can also set

up a variable in there we'll have a

string and we'll actually use that

string as a property name so straight up

JavaScript let's say we're going to go

with const prop name and we're going to

set it equal to age and now instead of

hard coding I can just go with prop name

so if I'm going to change the string

value now my property is also going to

change over here in a tiger and we can

do the same thing in type Alias I can go

with type

animal let's set it equal to our object

and then instead of hard coding we're

going to go with prop name and set it

equal to a number I just need to follow

the proper syntax over here and now

let's set up the type for a tiger and

we're good to go so just like in regular

JavaScript we can use computed

properties in type alas okay and up next

let's cover interface type which is used

to describe the shape of an object as a

side note we are purposely covering

interface type right after type Alias

simply because they are very similar and

yes before you ask quite often you can

use either one of them and the result is

going to be the same now what do

programmers do when the same thing can

be achieved in multiple ways well we

argue about it on Twitter and try to

convince everyone else that our solution

is somehow some way

better why because apparently that's the

best use of our time and remember if all

the other arguments don't work you can

always say it's just a better practice

to do it apparently that one always

works jokes aside I do personally prefer

type Alias over interface and therefore

during the course most likely you'll see

type Alias syntax more often but just

like I mentioned before it really comes

down to your preference despite what yet

another Twitter Guru says okay hopefully

I did not scare you away with my joke SL

rant and if you're still here let's set

up a book object so I'm going to

navigate to my

tutorial I'm going to call this deep

work and you'll see a second why so

we're going to go here with deep work if

I only would know how to spell this is

going to be my object we're going to go

over here with this

ISBN which essentially is just used for

books as the ID so in my case I'm just

going to go with one two three then

we're going to come up with title I'm

going to call this deep work as a sign

of this is an awesome book again I'm by

any means not being sponsored or I'm not

trying to sell you this book but this is

an awesome book uh you won't regret

whatever dollar it costs so we're going

to go over here with author that is

going to be Cal

Newport awesome and then let's also set

up the genre and I believe it's

selfhelp self and we're looking for help

now I do need to add over here a comma

and we already know how to set up ttype

alas so probably this is something we're

going to set up at the very end but we

also can use the interface again this is

something that we use if we want to

describe the shape of the object now the

keyword is interface then we come up

with a name same deal lowercase

uppercase totally up to you in my case

I'm going to go with the uppercase and

then instead of the equal sign we just

want to set up over here the curlies and

then same deal we go with the property

name and then the type and I write away

want to mention that the

readon modifier which we covered with

type alas as well as the optional

property is also allowed and therefore

I'll go right away with read only then

I'll Target basically this book ID and

I'll set it equal to a number remember

if we'll try to modify this value later

it's not going to work then also let's

set up a string okay beautiful that's

going to be 40 title then the same deal

we're going to do with author we're

going to set it equal to a string and

the same is going to be for genre but

I'm going to set it as optional again

just so we get this one out of the way I

don't think we need to spend a separate

video on these two things since we have

covered them before and effectively if I

go here where is my deep work and if I

set it equal to my book I'm going to go

so if for some reason I go with a deep

work and try to modify this property

which is read only let's say I'm going

to go with some value notice typescript

is going to complain same deal is going

to be if I'll try to add property that

doesn't exist let's say price and I'm

going to set it equal to

800 that is not going to work and then

let's say for genre since it's optional

property I can just remove it basically

comment out and my code is still going

to work and if you enjoy working on the

challenges you can set up a type Alias

for this deep work object and you'll see

that in this scenario you can use either

of those approaches and the result is

going to be exactly the same okay and up

next let's discuss methods in

interfaces and we're going to spend few

video videos on it just because it's not

in my opinion a complex topic but it can

be a little bit confusing because you

can set up methods as properties as well

so essentially you can mix and match and

at that point it might look a little

confusing so start with just straight up

approach which is my preference and then

I'll show you the alternative code that

you might see somewhere in the wild so

effectively if this book has for example

a method of print author I just go

directly to my interface in this case

I'm going to add a comment and I'm going

to come up with that method now please

keep in mind here we're not typing any

logic I'm just saying yes there's going

to be a print method or you know what

should be print author for some reason I

went with print method

it's not going to look for any

parameters and then as far as the return

it's not going to return anything it's

just going to log so the moment I do

that now notice I have typescript

complaining because I haven't set up

that method over here you know what just

so I have

less code I'm just going to remove those

comments over here so now let's set up

that method again this is going to be my

Approach where I go print auth

setup over here my method and in this

case I'm not looking for any prams we'll

cover that in a second and then we just

go with log and then since I'm not using

the arrow function syntax I can access

any of these properties over here by

using this again we're going to cover

the arrow syntax approach a little later

for now we just want to log the author

that's it so now let's go go right after

the object we're going to go deep work

then we're going to invoke print author

and if everything is correct we should

see in a console the author so let me

take a look at the browser and yep I

have my Cal Newport so my logic works

now what is the syntax if there's going

to be a parameter well let's try it out

in this case I'm going to go with print

title and I'm just going add some

message after the title I'll say this

book is awesome or something along those

lines so let's go here with

title we set up the parameter as a sign

note this name doesn't need to match

whatever we set up over here in the

instance so in here I'm just saying yes

there's going to be some kind of

parameter and I'm going to reference

this as message now type is going to to

be string and Just for kicks let's also

return from this function again we're

not setting up any kind of logic over

here I'm just saying that there's going

to be a method by the name of print

title so now we want to scroll down and

same deal we want to set up our function

so I'm going to go with print title and

I'm just going to call this value just

to Showcase again they don't need to

match now is my preference to set them

up the same yes but again that is just

my preference and then inside of the

function same deal in this case I do

want to return and notice how typescript

essentially is complaining that hey you

said that it's going to be a string over

here and at the moment it's still void

what's up with that so let me just

access again this dot since we're not

using the arrow function then we can

access nicely title and I'm going to

provide over here whatever message is

going to be passed in and then let's

keep on moving I guess right after the

print

author either we can log it right away

or in my case I think I'm just going to

store it in a result so let's go deep

work then print uh nope it's not the one

we want to go with print title and then

let's say

is awesome book so this will return a

string so what do we do with string

value well we log it and yes it looks

like everything is correct but text is

not so let me set it up properly or here

again if we have a method in here we

just set up the

blueprint so what is going to be the

method name whether we're going to

accept any parameters if we do then it's

useful to set up right away a type and

also whether we're going to return

something from this function or or no

and then inside of the instance we set

up the method and we just need to follow

our blueprint so if we're not returning

anything from this

function we just set up the

functionality if we are returning we

need to make sure that the types match

and with this syntax we can access any

Properties by using this keyword okay

and up next let's cover an alternative

way how we can set up method me in

interfaces now let me stress something

technically this video is optional I

just wanted to cover this because you

might encounter such syntax somewhere in

the wild but I personally tend to stick

with the approach we covered in the

previous video simply because I find it

way more

straightforward alternatively we can set

up the method in the interface as a

property how's that going to look look

like well we can go here with print

something and again the example is going

to be pretty straightforward and

essentially we set it here equal to a

function but please keep in mind this is

a syntax we're not setting up over here

the arrow function this is just the

syntax that we're using so we say that

it's going to return a number and then

we set it equal to some value and pass

in the number and now with this proper

in place we want to go to a deep work

object and here we have quite a few

options to set up this function so I'm

going to add these comments I'm going to

say First Option then there's going to

be a second option and I believe there's

going to be a third one as well but

we'll see most likely I will improvise

as we go so first option well we can use

the good old

function keyword so I'm going to go with

print something that's going to be my

property right now then I go with

function same deal it's looking for some

value now what is going to be the value

that will be a number correct and then

as far as the function body just so I

return a number essentially I'm just

going to go with some value now let me

scroll down a little bit I mean most

likely we can just remove these values

just so our console is less busy and I

can go with my deep work then let's go

with print

something we want to pass in some number

why not

34 and then let me set up the log and

let me move this sucker inside then let

me remove my semicolon let's navigate

here and notice I have 34 so again

instead of setting up the straight up

method now I set up the proper

which is equal to a

function in here if I have some

parameters then I set up the type and I

also say well what is this function

returning again you don't have to return

something from this function just

because it's a property right now so

that is going to be our first option

okay let's common this one out and our

second option is going to be Arrow

function so we can go here with print

something

remember we want to access the some

value that is going to be our parameter

and then as far as the logic I'm going

to go with some value now there's a

reason why I'm setting up the curlies

I'm fully aware that we can set up the

implicit return the reason for that is

because I wanted to Showcase

that there's a gacha with this and arrow

functions so Arrow function is going to

capture the global this please keep that

in mind if you're using Arrow function

functions unlike the good old regular

function where we right away have access

to this which is scoped to this instance

it's not going to be the case with the

arrow function so for example if you

want to access any of the properties in

my case I'm going to go with author

we'll have to go with deep work and then

the author now let's navigate over here

notice we have both we have the 34 and

we also have the author so this will be

our second option and I guess what was

somewhat

confusing is the fact that you can also

do another

way where I can go with print something

and effectively just use the syntax we

already used before so this also is

going to work and that's why again my

preference is just to use this approach

where I set up the method and I clearly

do the same thing inside of my instance

so this will also work so we can go here

with return and then some value print

something and notice once we navigate

back to the console this also works and

lastly I'm not trying to confuse you too

much but this also is going to work so

notice we have over here this print

author which is set up as a method but

we can set this one up as a property so

we can go here with print author now I

believe typescript is going to complain

so I'll uncomment the first one my

Approach I guess if I have a property

then we're going to go print

author and we will set this up as a

property and we'll set it equal to an

arrow function again not trying to

confuse you too much but just showing

you alternative syntax that you might

see somewhere again

remember we don't want to use this we

actually want to go with deep work and

then we're going to look for author now

tespt will complain since I already

have my first approach but again if you

navigate to the console you'll see that

the result is there now I'm not calling

print author that's the reason why I

don't have it let me go here let me

invoke it and you'll see that as far as

functionality it works again what's

confusing is that you can set the

property equal to a function so instead

of straight up method you set up a

property which is actually equal to a

function and then you can start doing

this mix and match where yeah it was a

property but then actually in here it's

going to be a method and then the other

way that's why my preference is to set

up methods with this syntax and and the

same in my instance just set up straight

up methods simply because in my opinion

it's just less confusing hopefully I

didn't lose too many of you and with

this in place now we can start working

on our next task okay and once we're

familiar with the interface fundamentals

let's work on a small challenge where we

want to set up a computer interface

inside of it we want to set up few

properties one is going to be read only

which is going to be for object then

brand equals to string Ram is going to

be number upgrade ram will be a

method and in there we're going to be

looking for number and we'll return a

number and also there's going to be a

storage property which is going to be

optional but the type is going to be

number also once we have the

interface we will set up the instance

and we'll provide the properties apart

from the optional one and then finally

we'll also invoke the upgrade ram method

so let's try it out let me set up my

interface name will be a

computer let's go line by line this one

will be read only so I'll set it equal

to my ID then brand equals to A String

after that let's go with the ram that

will be number okay then upgrade

ram this one will be a

method so we'll look for

increase and this actually is going to

be a number now from this function we

want to return a number and then also

let's set up the storage which will be

optional and we'll set it equal to a

number so now let's create our instance

in my case it's going to be a

laptop so set it equal to our object and

we right away want to set up our

interface type now let's pass in those

values there will be an

ID then a brand is going to be a random

brand after that we have a ram we'll set

it equal to 8 I guess 8 gigs and let's

also set up our method upgrade ram as

far as the parameter I'm going to go

with different name just so you can see

that for sure everything works even

though the names don't match and in here

let's just set up functionality where we

grab the current Ram value and we just

add the amount which is past in and then

since I want to return a number I'm just

going to go with this Dot and RAM this

is what we're

returning since the storage is optional

I'm not going to pass it in let's just

set up our instance then storage and now

I'm going to set it equal to

256 we can log it so let's go over here

with our laptop let's see yep I have my

object a brand RAM and everything up to

the upgrade RAM and also let's invoke

the upgrade ram let's pass in some value

and let's keep our console locked so

we're going to go over here with another

one I guess since we're returning the

value so let's go with laptop upgrade

ram let's pass in some kind of value in

my case I'm going to go with four and

then if everything is correct this is

what we're getting back from the method

and also our Ram instead of eight is

actually equal to 12 okay and up next

let's see how we can perform interface

merging how we can extend the interface

and then we'll work on another challenge

and during that challenge we'll see how

we can use typu with interface for

starters I want to create two interfaces

one for person and one for dog owner now

both of them will have two properties I

guess well one is going to be be a

method name and let's say details so

let's go with

interface I'm going to go with person

I'm looking for name I'll set it equal

to a string and also there's going to be

a get details method which will return a

string so that's my person one and I

also want to set up one for dog owner so

let's just go here dog

owner so that one will have a dog name I

guess that's going to be my property

name which is going to be string and

then instead of get details we're going

to go get

dog details let's invoke it and again

we're looking for a string over here

okay beautiful and first let's see how

we can merge the interfaces so once I

have my person one I want to create my

object I'm going to call this person and

the type is going to be equal to my

person interface now what are the two

values we need to provide first we need

to go with John and as I not I'm missing

here the equal sign and the second will

be the get details one so let's just go

with get

details that's the

function and we're going

to set up the

functionality with the template string

name

colon then let me access the this dot so

this do name and also let's add

age so this one will also be equal to

this Dot and then the

age now notice over here how we don't

have the age correct and one way is to

go back and set it up over here in this

person but there's another way how we

can add this property and that is by

merging the

interfaces and I know that this looks a

little funky in the beginning please

keep in mind that most likely you're not

going to do that in the same file but

let's say if you're getting the

interface from somewhere if you know the

name you can do something like this and

as a said note yes essentially I'm using

the same name I go with interface person

and then I just go with age now number

so I add that extra property over here

now this also needs to be in my instance

correct so in here I need to come up

with some kind of value and now the get

details is correct I can access both the

name and age so I have the first one and

then I just merge so whatever properties

I'm going to set it up over here yes

essentially if I create this instance

now all of these properties

will have to be there hopefully that is

clear now just a showcase let me go with

person Dot and then get details let's

invoke it and for some reason I don't

see anything in the console and of

course because I'm returning so what am

I doing here let me go with my log me

move this sucker

up and now let's try it out yep I have

name John and age is 30

and up next let's see how we can extend

the interface which is a way for us to

create a new

interface that inherits or essentially

just uses the properties and

methods from the existing interface now

it sounds more complex than it actually

is imagine the scenario we have an

employee

instance and for now we're not going to

set the type let's just set it equal to

an object I'm going to go with some kind

of name I'm going to go not with John

let's go with Jane over here then let's

also set up the age CU

remember we already added this to a

person so now essentially we need name

we need get details and we also need an

age so let's set up some kind of age

here then let's go with our details

however in this case since we're going

to add one more

property the return is going to be a

little bit different here's the thing

Jane is a person that kind of makes

sense correct so I can definitely set it

equal to a person and call it a day

however let's imagine that Jane since

she's an employee she also has the

employee ID now I don't want to add it

to a person so I want to keep this as a

separate interface but I do want to use

all of the properties that I already

have in my person one and just add on

that employee ID so here's how we can do

that we go with

interface then come up with a name in my

case I'm going to go with employee and

then we go with this extends and now

we're just looking for a specific

interface we want to use and now let's

just add this

employee ID and set it equal to a number

so now Jane not only she's going to be a

person but she's also going to be an

employee so now when we set up the type

we go with employee and now not only I

have name and age but I also need to

apply this employee ID so let's add this

one let's say over here 1 two 3 and then

remember details needs to return a

string so in this case I'm just going to

grab whatever we have over here and then

let's just add the employee ID as well

so let's add a

comma we're going to go with ID and then

let's access this Dot and then employee

ID now just so we can see that

everything works I guess instead of

person

details let me go with

employee get details and yep and have

all three values in the console now we

can also inherit from multiple

interfaces essentially I can extend from

the person as well as the dog

owner so we're going to go with a

manager instance I guess so we're going

to go here with

manager eventually we'll set up the type

for now I just want to provide a name

it's going to be equal to a bob and also

for now let's go with the AG which will

be equal to

A35 now when it comes to

Bob not only is going to be a person so

we'll need to provide all of the

properties but also let's imagine that

he's a dog owner so essentially we want

to extend from both interfaces that we

already currently have the person and a

dog owner now since Bob is a manager I

also want to add a a method onto the

interface and in my case I'm going to

call this manage people so let's move

where we have Bob and first I guess

let's construct the interface and then

we'll worry about the properties so

we're going to go with interface manager

for stars let's just add that method

that I was talking about so I simply

want to go with manage

people uh it's not going to take any

parameters and we're not going to return

anything and if we set this equal to a

bob we'll have an issue since we have

two properties that we haven't set up in

our interface so now let's go with

extends and one by one let's look for

those interfaces so we're looking for a

person and a dog owner so Bob is a

manager a person and a dog owner and now

if I navigate over here and set it equal

to manager type I will have to provide

all of these values what they are well

we need to provide a dog name let's go

direct Rex it's a super popular name

then we also have get details and you

know what in this case I will speed this

up I really don't want to type

everything from the scratch so we have

get details what do we want to access

here I guess let's just go with age

since we don't have the employee ID then

we also have one for dog so let's go

with get dog

details now we will go with name is and

then let's access the dog

name dog name over here then let's

remove the age guess we don't need it

and lastly let's set up that manage

people manage people let's invoke it and

for now we simply want to log so let's

set up a console log and let's write a

text managing people and lastly just to

test it out that everything works want

to go with manager and it's invoke

manage people if everything is correct

we should have this text in a console

and again this is how we can merge

interfaces by essentially using the same

name and just adding the properties

another name that you might hear is

reopen essentially they mean the same

thing where we declare the interface

with the same name one more time and

then typescript is going to merge them

together and we can also extend so let's

say if we have an interface with some

properties and methods and we just want

to grab methods and properties from some

other interface simply go with extends

we look for that specific interface and

in the process we'll right away get

those methods

and properties and with this in place we

can move on to the next task and up next

let's work on another

challenge and during the challenge we'll

see how we can use

typu with

the interface now I did split up the

challenge into multiple videos so in the

first video we'll kind of prepare

everything we'll set up our function we

will will return one of the interface

types and then in the following video we

will work on more logic where we'll see

how we can use the typ guard so I didn't

want to jam everything in one video

because there's quite a few lines of

code

and I mean the most important thing is

kind of at the very end and usually if

it's a long video then people just lose

the interest so long story short we want

to define a person interface with the

name String then we want to set up a dog

owner which extends the person and just

add the dog name which is going to be a

string and also we want to set up a

manager which extends the person so not

person and dog owner no the manager is

going to extend only the person and

we'll just add two more methods on it

then we want to set up the instance

which can be either of them so we'll use

the Union type and actually we'll set it

equal to get employee function now in

there in get employee we'll just call

math.random and based on value we'll

return one of those interfaces so

whether a person dog owner and a manager

and again in the next video we'll see

how we can use the typ guard because

there's a

gacha that we need to be aware of STS

let's navigate to tutorial one by one

let's set it up so this is an interface

we want to go with person let's go with

name equals string okay then let's also

set up a dog

owner so we have here

interface dog owner now that one will

extend the person so we'll get that name

property and we also want to add the dog

name dog name will be equal to a string

and then the last interface is going to

be a

manager which is going to extend the

person and in here let's go with manage

people that's our method and we're

simply going to go with void and also

copy and paste and let's say delegate

tasks so those are our two

functions and then let's set up our our

instance but before we do that let's

also set up a function and I'm going to

call this get

employe and this is the function that

we're going to use in our employee

instance so for starters I'm going to go

here with const

employee and as far as the type I'm

going to use the union type so either

it's going to be a person or it's going

to be a dog owner or it's going to be a

manager and I'm going to say it equal to

my get employee and I'm going to invoke

it now I didn't want to move this

function up simply because in the

following video we'll write the code

over here and I think it's going to be

less confusing so let me move it up

that's going to be our function and

here's the task inside of the get

employee I want to

invoke math. random and then based on

the value if it's say less than

0.33 well then I'm just going to return

a person interface if not then it's

going to be a dog owner and if not then

it's going to be a manager so I have

this employee notice over here it just

says well the moment you're returning

void

and that's not what the employee is

expecting so in here I'm looking for one

of these three

values now in this get employee we're

not not going to pass any

parameters simply want to go with our

logic so let's set up the random that

one will be equal to math. random so

we'll get some random value between zero

and one and now let's just work on those

returns but also let's set up the type

right away so we're looking for

person we'll also grab the dog owner and

potentially this could be a manager so

again we don't know what the value is

going to be so every time we'll refresh

the browser we'll get some random value

over here and then based on that value

we'll set up that return so let's start

with our first option if the value is

less than

0.33 well in that case I want to go here

and I want to return a name John so

which interface is that well that's the

person one correct so these two match

then let's also set up another else

if so if the random is less than

0.66 in that case let me grab this and

now we just want to add the dog name so

in this case we're going to go with

Sarah and we're going to go with dog

name and we're going to set it equal to

Rex now

lastly if it's not less than 0.33 if

it's not less than

0.66 then we're going to go with another

else and in here we want to return a

manager interface so in this case we're

going to go with return Then object name

will be equal to a bob and then let's

set up those two methods we're going to

go with manage people and as far as the

logic let me just go with console log

and we're going to say managing

people dot okay good and then let's do

the same thing for delegate

tasks that's my function and as far as

the text it's going to

match now let me navigate where I have

the employee and let's just log it like

I said we'll have to refresh the browser

so once I navigate over here notice this

was my person instance then I get over

here the manager correct then I get the

dog owner and as you can see every time

we refresh the browser we're getting a

different value so in here

again we want to set get employee and we

want to make sure that we only return

one of these interfaces we use the unit

type and then when it comes to the

instance same deal I'm looking for one

of these three values so employee is

going to be either a person a dog owner

or a manager and in the following video

we'll introduce the typ guard and make

this challenge more complex okay and

with this in place now let's make this

challenge more complex by adding a

function which is going to check for

specific interface and only if it's a

manager we want to invoke delegate tasks

because here's the kicker we get back

our object we store it in the employee

and if we try to go with name everything

works why well because dog owner extends

the person manager extends the person so

that property will be definitely there

we can navigate to the browser we just

need to refresh and eventually we will

see all three values but it's different

with delegate tasks so notice once you

start typing typescript is complaining

it says well listen it could be either

the person or a dog owner or a manager

so you don't know that 100% the delegate

tasks is going to be there at runtime

this is why we want to set up a function

and we'll start with somewhat

straightforward approach and then we'll

cover why we want to use type predicate

so let's go here with a function my

okaye I'm going to call this is manager

so I want to make sure that it's a

manager and then in the if block I'm

just going to invoke delegate tasks

That's My overall goal so I'm going to

be looking for object because this is

what we're getting back from employee

but same deal as far as the parameter

well it can be one of these three

interfaces okay then as far as the

return like I said for now let's just go

with the straightforward approach where

I'm going to go with Boolean either it's

going to be true or false and I guess

the first gotcha in here is the

return remember previously when we used

the typ guards we did something like

this we went with type of then object

and set it equal to something now is it

equal to what object well all of them

are objects so that's not

specific so if I invoke his manager with

employee this should return for all of

them pretty much the same value let's

try it out we're going to go here with

log is manager then let's pass in the

employee and let's take a look at the

console notice as I'm clicking I'm all

the time getting true so yeah this time

guard is great but it's not going to

work in this case so if we want to check

for manager we want to look for

something

specific and that something specific is

one of these methods and the syntax is

following where we want to go with the

method which will pass in the string and

in and then the parameter in this case

object so now let's correctly type one

of the methods in my case manage people

and now let's navigate to the browser

and again once we refresh we'll actually

see correct

results only if the interface is manager

then we return true and if it's not the

case then we return false but there's

another gotcha so now let's go and set

up if block I'm going to go with is

manager I'll pass in the employee pretty

much our setup and then let's try to

invoke

employee and same deal I don't have

delegate tasks for some

reason let me try to invoke it and again

typescript is complaining so here's the

deal yes our logic over here is correct

but just because we return a Boolean

from this function doesn't automatically

signal to a typescript that now

employees actually type of

manager and here basically yeah we

passed the if condition but as far as

typescript is concerned it it can be

still one of these three types and this

is where type predicate is super useful

and that is a special kind of return

that not only returns a bullion but also

it

asserts the argument to be a specific

type so what am I talking about in here

instead of the Boolean we can go with

object that's going to be the syntax is

and then since I'm checking over here

for the

manager that's the interface I'm going

to use and now typescript definitely

knows that once we pass this condition

this will be a interface manager so once

I navigate back over here going to

refresh once I'm getting back the

manager I'm also logging delegating

tasks okay and at the very end of the

interface section I also want to cover

the differences between the interface

and the type alas so if you're setting

up the object since interface is used to

provide the shape of an object you can

use either of them so if I have object

John with name and age I can either use

the Alias type person or I can use the

interface person now as far as the

differences you see type alas we can

also set up for primitive types for

example if I have number or the union

type number or string and the literal

types you won't be able to do that with

the interface so that's the first

difference again when it comes to

interfaces they're useful to provide the

shape of an object but you won't use

them with the Primitive or with the

literal type now with interfaces we can

merge them together like we covered

before or another word is to reopen them

you won't be able to do that with the

type so with the interface you can set

up the interface you can add some

properties then I don't know three lines

later you can create the same interface

basically with the same name just add

more properties and you're good to go

that doesn't fly with the type that's

another difference now as as far as the

interfaces they can be implemented by

the classes while the type aliases

cannot be implemented in such way so if

you work with classes this is something

to keep in mind you can use the

interface with the class but you won't

be able to implement the type Alias with

the class and lastly remember when we

covered computed properties you can only

do that with type Alias so you won't be

able to use the computered properties

with the interface and with this in

place now we can move on to our next

topic okay and up next let's discuss

Tuple or Tuple in typescript which is a

special type since we don't have it in

JavaScript and essentially it allows us

to set up an

array with fixed

length and ordered with fixed type in

other words it's super useful when we

want to group different types of values

together so for example I have a let

person now this is an array and here I

have string of John and then number of

25 I can set the type in such a way

where I go with my array and then I

provide those values so in this case I'm

going to go with string and number so

now this value is fixed so if I'm going

to try to add something else like hello

typescript is going to complain if the

types are not going to match if for

example I do decide to place 25 over

here typescript also is going to

complain so not only we have fixed

length but also we right away set up the

fixed types so now this value can be

only the string and number now there is

a gacha something I'm going to cover in

a second but for now let's just focus on

this that yes it's going to be John and

it's going to be 25 now you're not

limited to only two values over here you

can set up as many as you want and for

example you can go here with number and

number I mean that's also an option

let's say you don't want to have just an

array of numbers but you want to have an

array with fixed amount of numbers so

let me just go here let's say with

date so in this case it's going to be

number number and number and then

depending where you live either you'll

pass in the month or the day so let's

say I'm going to go 12 then

17 and then we're going to go with

2001 so notice now this is a fixed array

with number number number so again if we

make any changes that typescript will

complain about it now it's useful if

let's say we want to return something

from the function let me go with

function get person and we're not going

to provide any parameters I'm just going

to say that yeah this function is going

to return an array with such types so

string and number so now let's set up

the function body where we want to go

with our array we want to pass in John

and we're going to go with our

25 so now if we have random person now

and that one is equal to a get person we

invoke it if we

log random person and then zero copy and

paste and one in a console we should

have both of those values now like I

mentioned the gotcha here is that even

though when we're hardcoding these

values typescript is going to complain

unless we provide over here this read

only we can actually add items or remove

items from our particular array so how

is that going to look like well let's

say if I go with date.

push I can add the values and typescript

actually is not going to complain about

it now it complains because it's not a

number right so it says well it's not a

number but if I change this to do my 34

everything is going to be fine so I can

set up multiple instances and now if I

loged the date check it out it's

probably not something that we expected

now the workr is to provide this readon

over here so in this case I cannot do

that so once we add this

readon we cannot use anymore the push

pop or whatever methods that's something

to keep in mind now lastly I also want

to mention that we can use the

optional parameters as well so let's

say if I'm going to create a new

instance and I'm going to call this

Susan so I'm going to go with my Tuple

we're going to set up a string number

and in here I'm just going to go with my

optional parameter once I set it equal

to my function notice I can just provide

the string and basically I'm good to go

typescript is not complaining this

should do it for tuples in typescript

and up next we're going to discuss enums

in

typescript okay and up next let's

discuss enums in typescript against

something we don't have in JavaScript

and essentially enums allow us to define

a set of named constants the syntax as

following we want to go with keyword

enum then let's come up with a name in

my case I'm going to go with server

response status since we'll have a

little bit of functionality so we're

going to go with response

status then we want to go with the

curries and this is totally up to you

you can go all lowercase you can

capitalize the first letter or you can

go all

uppercase totally up to you we just need

to provide divide over here the values

and in a second I'll show you what this

actually results

to so first one is going to be success

and then the error now we can add more

but for our example we really don't need

it then let's set up the

interface in this case I'm going to call

This Server response and then the first

property result actually is going to be

type of enum so let's set it equal to to

server response status and then another

one is going to be a data and this will

be an array of strings so now let's set

up a function get server response which

actually is going to return this

interface so we go here with function

get server response let's invoke that as

far as the return type let's set up the

server response so this is equal right

now to our interface and then inside of

the function body we want to go result

and now since this is type enum over

here this is what we want to use so we

go over here with server response status

and notice we either have error or

success again you can use enm if you

want to store some constants and then

later on use it in your project so now

in this case we only can provide success

or the error so let me type this one and

then in order to match our interface

I'll provide data as well I'll say first

item then comma and we're going to go

with second item now I do need to add a

comma over here we do want to invoke it

and set it equal to response

const response is equal

to our get server response let's invoke

this function over here and let's set up

the type what we're expecting so we're

going to look for our interface and then

let's

also log the response just because I

want to show you the potential values we

can set up over here so at the moment we

have success and error and by default

they

actually get the numb starting with zero

and I'll show you what I mean in a

second so first let me just log the

response and notice how the result is

zero

now why is that well because if we go up

over here and we log server response

status we'll see that we have right now

the success and error and the values are

zero and one so it starts with zero then

one and then pretty much the more values

you add well the more numbers you're

going to have now don't be surprised if

you see quite a few values in a console

ENT

at the moment we have four of them this

is something we're going to discuss in

the upcoming video for now I just want

to showcase that even by default you get

those values starting with zero so 0 1 2

3 and whatever you can also reassign

them so for example I can say that

success is going to be equal to a 500 or

I'm sorry 200 and error is going to be

equal to 500 or I can mix and match I

can say that yeah error is actually

going to be equal to this string this

also is valid and again the main point

is that now we have over here this

constant which we can use all throughout

our project instead of trying to make

sure that we type the string or the

number correctly okay and up next let's

take a look at the gacha with enams

which is the fact that when you have

number values it's actually going to do

the reverse mapping

and remember it is the default so if we

don't provide anything we will get that

reverse mapping for example if I provide

over here 200 and 500 if I navigate to

the browser again I have more values

over here in this object so not only

error and success but I also have this

reverse where number is actually a

property and then whatever is my

constant name is set as value now why do

we care well because let's say we want

to iterate over the values in JavaScript

we have object. values and then we pass

in the object in this case we'll pass in

the inum and you'll see that everything

is going to work but it's going to

depend what kind of value we have over

here if we have a number we'll have to

do an extra check so let's go here with

object dot values then let's provide

server response status and we're going

to go with for each so we're iterating

over now I want to grab every value and

we'll just log

it and again since I have the number

values I have this reverse mapping so

now not only I have the number value I

also have this success and error and

it's not going to be the case if

let's say we're going to go here with

success and in here error again

something valid that you might set up in

your code now everything is correct now

we're only accessing that string so if

we have numbers which again is the

default setup so again let me set it up

here as 200 just so we're on the same

page the solution over here is just to

add another another typ guard so if I

only want to access the values they are

type what their number so this was going

to be a string therefore in here I'll

say if type

off and value that was the name of my

parameter if it's equal to a number well

then I want to log it or do some kind of

functionality in this case just log so

we're going to go with console log and

we'll log the value so now we

correctly just access those number

values now another place where we need

to be careful is when we're setting up

the value so notice something

interesting if I have an

enum I have a constant over here and the

value is number then later when I set up

this enum as my type I can still use the

good old number so this is going to work

because again typescript is doing that

reverse mapping however if you have an

enum where the constant value is

actually string this is not going to fly

so just to Showcase that I think I'll

comment this one out so if I have here

200 and 500 if I set up over here this

result to be equal to my enum I can go

to my server response and this is going

to work work so typescript is not going

to complain about it and I can see that

my code runs and everything is awesome

however if again and I promised for the

last time we'll change it around we go

with success and error this is not going

to fly if we navigate back to our get

server response and try to provide the

string value as you can see right now

typescript is complaining so we cannot

assign string to a type enum however

when we use the number value it's going

to work because there is this reverse

mapping hopefully that's clear and now

we're ready to move on to the next topic

okay and now let's work on our next

challenge where we want to define a enum

with the consant of admin manager and

employee Define the type Alias named

user and in there we'll set up the ID

property name as well as the rooll and

the RO is going to be equal to our enum

and also we'll set up the contact which

is going to be a tuple on two elements

the email which is a string as well as

the phone then we'll set up a function

by the name of create user which will

take in the user object as a parameter

and return the user object and then at

the very end we'll call the user object

provide the object object and we'll

create the instance so in tutorial I

think I want to start by defining that

enum here let's call this

user role let me set up my constants

here and I think I'm going to rely on

those default values so 0 1 two and I

guess in this case that's going to be it

only going to be 0 and one two then we

also want to go with

employee after that let's set up that

type alias in this case

user here one by one let's set up those

properties ID is equal to a number then

we also have name is equal to string

we're going to go with roll and in this

case it's going to be equal to a user R

so one of

our three constants and then we also

want to go with contact and we set this

one up as string and string we have

create user function so let's set it up

over here create user and this one is

looking for a user parameter which is

going to be type user same deal over

here we're going to go with user and

from the function we'll return the user

and the last step is to create the

instance so let's go with the user which

will be type user let's call create user

and now let's provide the values

ID name John do then also we'll have a

roll and since we're using our enum

we're just going to set it equal to user

R then Dot and one of the values in my

case I think I'm going to go with admin

one and then at the very end we also

have the contact I want to set it equal

to our array and let's just provide some

values gmail.com comma and then we're

going to go with 1 2

3 four 5 six and 7

89 the very end let's just log it and

pre sure everything is going to be

correct Yep looks like I have the

correct value and with this in place

we're ready to move on to the next topic

and up next let's cover type assertion

which is a way way to tell the browser

what type an existing variable is and

this is especially useful when we know

more about the type than the typescript

does as a side not it's very handy with

dom elements so if these examples don't

seem that convincing in the later

sections we will cover different

examples as well so let's imagine the

scenario we have a variable and I'm

going to go with some value and for some

reason type is any now as far as the

value I'll set this up as a string so

this is a string and then in the next

line I want to get the string length

which actually is going to be a number

so in here let's set it up type is going

to be equal to a number and now I want

to go with DOT length but I want to

assert to a typescript that actually

this is a string so I'll say some value

and not just any type I'll say as string

so the keyword we're looking for is this

as that's the assertion where we tell

typescript that yeah I know that maybe

this is not something you expect but I

know more and I know that this is the

specific

type this is also something that we can

use for example with the Json parse

because it returns any so let's say we

have a type bird now this type bird only

has a name and we'll set it equal to a

string now it looks like I have a type

over here so let me set it properly and

now I'll set up two Json strings and

we'll run pars now in order to speed

this up I will grab those values from

the read meor here so basically we have

bird string and a dog string we want to

set it up over here and now again once

we'll run Json pars you'll see that type

actually is any so let's say I have a

bird object and that one is equal to

Json then parse and now I'll pass in my

bird string so again let me copy and

paste and let me set up one for the

dog and as we hover over like I said

type is any but I don't want type to be

any I actually want this to be a type

bird so if we create an instance or any

other functionality and we set it equal

to a bird object instead of just leaving

it as type any I can go with as and then

my type because I clearly know that yeah

maybe I'm getting this back as type any

but I know that the signature matches

whatever I have here for the type bird

now please be careful you can also do

something like this where you can set up

the dog to be a bird and most likely

that's not the behavior you want so if I

go here with not bird object I'm going

to go with a dog object and I'll set it

equal to a bird I will be able to look

for dog. name but if we take a look at

the dog string it doesn't have that

property so it has the breed so if we go

here with log and we type bird name and

as I said for some reason it's

complaining it says cannot find bird and

yep it's because for some reason I named

it bed so let me go here with bird and

also a dog notice how typescript is not

complaining because

I made a type assertion that yes this

will be type bird even though we can

clearly see that it's actually type dog

now we don't have the type yet but you

get the point so if I navigate right out

of the browser notice how I will get

this unexpected

undefined at runtime and at the very end

let me just show you a use case that I

just encountered when I was working on

my next JS project so in there there was

a enum and I believe the name was status

don't quote me on that and there were

more values but I'm just going to set up

two so we don't have to spend all day

typing and essentially there was a

constant and I set the values equal to a

string so there was pending I believe

interview declin but we're just going to

go with these two so we're going to go

with declined and we'll set it equal

also to a string so I had this enum and

then I was just adding it to I believe

it was the job instance and I was saving

it in a

database now here's the kicker when I

was saving actually in a database I was

saving it as a string because that was

the value for my status pending and then

when I was getting back the value from

the database it was already a string but

I needed to reassign this value to one

of the instances and at that point

typescript was complaining because they

didn't match and if this doesn't make

any sense let me just

showcase let's imagine that we have a

user object and in there I have two

things I have name String and also

status is now going to be equal to a

type status so we know that ually we can

use status. pending status. decline

everything is nice but since these

values are not numbers we don't have

that reverse mapping so if we'll try to

set this value as a string it's not

going to work so now let me quickly

navigate to read me and I just want to

grab these two comments over here again

just so we don't have to type this from

the scratch imagine this scenario now we

save status pending in a database but we

save it as a string so we'll save this

value over here then we get it back from

the database and

now I'm going to go with the status

value and I'll set it equal to the

string value of pending so effectively

this is what I'm getting back from the

database again kind of makes sense

correct because this is the actual

string value now if I'm going to go here

and set up my user instance and set it

equal to my user

type yep I typed the name everything's

correct but if just going to go with the

stat is equal to a status value notice

how typescript immediately complains

type pending is not assignable to this

type so typescript doesn't know that I

saved in the database as a string so I

know for sure that it's the value that's

going to

match the constants here in the status

TPT doesn't know that it just says Hey

listen status here is type status so you

cannot set it equal to a string and this

is where the assertion is useful where I

say yeah it is a string but I know for

sure that is type status so again type

assertion essentially is a way to tell

the typescript that we know what the

type is that we know more about the type

than the typescript does okay and up

next let's cover type unknown which is a

type safe counterpart to type any so

just like type any we can assign any

value to type unknown but the difference

is that before we can use the variable

with type unknown we need to perform

some type checking which again avoids

the unnecessary runtime errors so let me

go to tutorial and in here I want to

create a variable and I guess in my case

I'm going to call it unknown value so

that will be my

name and as far as the type I will set

it equal to unknown so just like with

any I can go here with unknown value and

I can set it up for example to be a I

don't know a hello world so Yep this is

allowed I can also go to a next line and

set it equal to for example array that

is also allowed so let me set up my

array I'm going to go with numbers okay

good and then also we can set it up to

be a number so let me go with 42 and

then let me add some numbers after your

D dot so this is allowed now the

difference is that I cannot go over here

and say unknown value and then set it

equal to a fixed as we can see

typescript complains it says Hey listen

that type is unknown and right away

you're running some kind of method how

am I supposed to know that it's actually

a number and we can run this particular

method I mean maybe it's still a string

so the difference again unlike type any

before we can use that value if it's

type unknown we need to check what is

the type so in this case we can do

following operation I can go type off

and then unknown value and I can check

well if it's a number well then I want

to run my method so let me move this

sucker down and notice now everything

works because in this condition

typescript knows that yeah unknown value

is actually a number now one place where

we'll definitely see type unknown is in

the try catch block because by default

typ scrip is going to set this error to

be unknown now why do we care about that

well what is typically the first thing

we do over here go here with log

and then error and then the message and

notice how T says well error is type

unknown so how do you know that there's

definitely going to be over here this

message property and this assumption

comes from the fact that typically

especially if we're throwing our own

errors over here we use the following

code we go with throw new error and

provide whatever message and in this

case I'm going to go there was an error

so this is is a nice assumption but

please keep in mind that JavaScript can

also do something like this we can go

with throw and some string over here and

I know what you're thinking well there's

no way I'll do that in try clatch block

yeah but you might be running some code

from third party library and at that

point you don't know whether the error

you're going to be getting back is going

to be the instance of the error class or

it's going to be something else again it

literally can be a simple string now to

demonstrate that I will use somewhat of

a silly example where I'm going to set

up the function over here I'm going to

go with run some code so let's imagine

that we're saving an image in a database

or I don't know we're posting some data

somewhere or sending an email or

whatever and in here I'm just going to

set it equal to I Rand them then let's

go with math. random let's invoke that

and essentially if it's less than

0.5 then I want to throw a new error if

not then I'll just throw good old string

so let's set up over here if

else and let's check for random if it's

less than

0.5 then I want to use the

seconder let me set it up over here and

if not then I'll just go with throw and

we're going to go with

some error so let me save this and now

in Tri block let's go with run some code

and effectively in here in a catch we

want to check whether the error is the

instance of the error class and if

that's the case yeah then we'll have

access to the message in this case there

was an error and if not well then we'll

simply log and provide some hardcoded

error and this is essentially what

you're going to do when you're working

with typescript

before you do something with that

message you want to check whether the

error you're getting is actually the

instance of the error class so here in

the cach block we want to go with

error instance off we're looking for the

error and then if that's the case yeah

then tcri knows okay there is a message

property and here we can go right now

with log and and we can set up the error

do message now if it's not the case

since I already have some text I'll

simply log the

error let me log it so now let's

navigate to the browser and check it out

depending on that math random either

we're going to get there was an error or

we'll have that string some error and

again just like any type unknown can be

anything but before we can start using

type unknown we'll have to do some type

checking and therefore this is a type

safe alternative to type any and up next

let's cover type never which is a

special type that represents the type of

values that never occur now I'm not

going to Sugar Code it especially in the

beginning this entire concept might seem

pretty confusing but hopefully after we

cover one of the most common use cases

of type never it's going to be easier to

grasp the main concept of type never for

starters let's just establish that if we

have a variable with type never we

cannot assign value to it so let's say

if we set up a variable some value and

if let's say it's zero if I'm going to

go with type never typt is going to

complain and I'm going to get the same

result regardless of the value over here

so this can be hello world this can be

an array doesn't really matter we cannot

assign any value to type never so that's

the first thing we need to remember

second you might encounter in your own

code Type never if you set up one too

many conditionals speaking from the

personal experience so let's say you

have a type theme over here

and you set it equal to two possible

values either is going to be light or

it's going to be dark then let's set up

a very useful function called check

theme yes we'll say that theme parameter

is going to be equal to our type of

theme now we're not going to return

anything so I'm just going to set it

equal to void and then inside of the

function I'm going to set up two

conditions I'm going to go with well if

theme is equal to and then I'm going to

go with light one and I'm not going to

be particularly original I'm just going

to go with light theme and then let's

return from the function and we already

know that typescript is super smart it

knows that at this point theme can only

be value of dark correct because these

are the only two options but let's

imagine scenario where we do add another

condition I'm going to go with if theme

is dark okay good then I want to log it

but I'll change the value and I'll also

return let me change this one around let

me go with dark theme and notice

something interesting if we type theme

after both of these conditions

typescript says Hey listen theme is type

never because we have handled all of the

possible cases

so at this point in time there is no

possible value for the steam so if you

ever encounter such scenario you'll have

to go back and look at the original

value and also all the conditions you're

setting up because somewhere things are

going south if you are at the point

where variable is type never well then

you already have handled all the

possible cases and what's really awesome

we can actually use it to our advantage

the fact that we cannot assign any

values to never and also the fact that

typescript will immediately assign type

never if we cover all of the possible

conditions as far as our example we're

going to go with enom I'm going to set

it equal to a color we're going to go

with red and blue so those are two

possible values now we can assign it to

a string but there's really no need then

we want to set up a function in my case

I'm going to go with get color name as a

I not I'm just going to set up a switch

statement where we check for possible

values but if you work with Redux you'll

find this example very similar to how we

set up the Redux store so as far as the

type for my parameter it's going to be a

color and inside of this function I

simply want to go with

switch I want to check for my color and

let's set up our cases so at this point

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

with color. red so if the color is red

what do we do then well then we want to

go with the return

Red so let's set up our

colon

return and we're returning the string of

red and if it's blue well then let's

just change it around so let me select

these

two and let me just go with blue then

let's set up to console logs iess let's

invoke get color name and we'll pass in

color then red and we're going to copy

and paste and set up blue as well and

everything's awesome if we take a look

at the console yep we have red and blue

but what if sometime later we go to a

color and add green and notice

everything is valid not breaking any

rules over here the problem is going to

be here when we invoke

it this is going to

fail but the worst case it's actually

going to fail silently so if we navigate

right now to the browser we can see red

blue and undefined why well because

we're not handling the case over here

and again this fails silently so we set

up nicely an additional enm we correctly

pass it in and then unexpectedly we're

getting an error correct and if you're

familiar with such code you're probably

screaming at me you're like Hey listen

just set up the

default case and throw the error and

you're correct before typescript that

was the approach so let's go here with

default then we go with throw new

error and for now let's just take a look

at the color and all of the is nice but

keep in mind this is again happening at

runtime so yeah we have this default

case where we throw the error if none of

the conditions match but I actually

would like to do that while I'm writing

the code not when my application is

running so we can definitely keep this

one over here but a typescript approach

is to come up with the variable and I'm

going to go with at build time here and

me add another comment and in here I'm

going to go with at

runtime and in here we want to set up

another variable now the name is really

up to you but I'm going to go with

unexpected

color the type will be equal to a never

and I will assign it to the color and

notice how immediately typ script

complains why well because initially we

only had two values so if we go back to

this one everything is

correct I only have this yellow squiggly

line which is totally okay but if I'm

going to add this green one then right

Away tab script is going to yell at me

because now I have one more condition

and of course we already saw that if we

don't handle it over here then

essentially we will throw that error at

runtime so what's the solution well we

go with another case

let's go color

green and same deal just want to go with

the return and return a string in this

case it's going to be a green one and as

you can see the moment we shut up our

cage types doesn't complain anymore

everything is fine because we have three

possible enums and we're handling all of

those cases in our get color name as

well so essentially this is a great

benefit for us where we can check for

those potential errors at build time

instead of just runtime okay and up next

let's switch gears and quickly discuss

modules and typescript now if you are

familiar with how es6 modules work most

of the things we're about to cover will

be a nice review but when it comes to

modules and typescript there are some

GES

we need to be aware of and let's start

with the main one you see by default in

typescript files are not modules they're

actually treated as script in a global

scope so what does that mean well if I

go to a source come up with a name for

example actions TS come up with some

random variables one is going to be

Susan then second one is going to be

something so let something is equal to

something if I create another file or in

the tutorial try to use the same

variable

name not going to be successful so

typescript is actually going to complain

so it doesn't treat this file as a

module so whatever I set up in my files

is actually put in a global scope which

obviously limits the variables I can use

I have Susan over here and I also have

Susan in the actions and therefore

typescript is complaining so pretty much

think of it this way everything that you

put in the files by default again we'll

fix that in a second but by default was

actually put in the global

scope so in order to fix it we have two

options we can go to TS

config and essentially set the property

or we can add the export and import and

the moment we add export and import then

they're treated like typical es6 modules

now also don't be surprised about this

gotcha where let's say in

tutorial you'll try to come up with the

variable with the name of name and you

won't be able to even though technically

in actions we don't have this value over

here you see such name is used in

declaration file again something we're

going to cover a little bit

later and again we have this name

Collision because typescript doesn't

treat this file as a module so

essentially unless we change that

there's going to be some keywords that

we cannot use and this was

super confusing to me in the beginning

because as I started learning typescript

I wanted to use this name variable and I

got this red Squigly line and I was like

what's happening over here why I cannot

use this name one I mean there's

technically no error and again let me

repeat for a third time it's because by

default typescript is going to

essentially treat the files as just

scripts in the global scope so once we

know the issue how we can fix that like

I said we have two options over here we

can either go to TS config and add the

property and you know what let me just

first showcase is how this would work

with Import and Export if we add export

or import statement to our file

immediately typescript is going to

essentially treat this as a module so

for example if I'm going to go back to a

tutorial and if I'm going to go with

import and I believe this one was the

named export so we're going to go with

something from the actions everything is

awesome so notice we don't have the

issue anymore with the global scope

correct so now these ones are scoped to

tutorial and then these ones are scoped

to the actions hopefully that is clear

so this is one approach now what if I

don't want to add Import and Export like

force it in a way well then we can go

over here to TS config and we're looking

for the property by the name of my

module detection and we want to go with

Force so by default it's going to be set

to Auto but we want to force it so in

this case even if there is no export

statement everything is going to work so

notice now of course I have different

complaint because I'm importing from the

actions and there is no export but the

moment I save I can use the name even

though it's technically used in

declaration file which was the issue

before

and I don't have this name collision

with actions anymore as well so I have

Susan over here and the same is in

actions again few

approaches we can either add the

property in TS config or if we add

Import and Export then immediately

typescript is going to treat it as a

module okay and once we're familiar with

the main gotcha let's just see how we

can use es6 modules in typescript and

like I mentioned before if you are

familiar with the main

Concepts this is just going to be a nice

review now before we start typing away I

do want to mention one property in the

TS config which is module and at the

moment notice how we have the value of

es next now this property controls what

module syntax is set up in the out put

code so effectively once the typescript

is done compiling our code so if I

navigate to a playground notice I have

my export statement over here where I'm

exporting some function and this is

going to be the result now if I go to TS

config and change from es next to for

example commonjs and as a sign not if

you're not familiar with

commonjs it used to be the main module

syntax in node.js but even no. JS is

right now slowly but surely switching to

a es6 module syntax and notice the

moment we change it actually this will

be the output so this is a common JS

syntax so if you ever have a use case

where you want to use different module

syntax in the output code just look for

the module property something I wanted

to mention and now just go to actions

and set up few values we want to export

and then in tutorial we will import them

again just to have a nice review how the

es6 modules essentially work just so you

can see that pretty much the idea is

exactly the same first I want to go with

um some kind of function I'm going to go

with say

hello let's set up name equal to a

string and you know what I'll also say

that we're not returning anything from

this function in here we're going to set

up a nice console log we're going to go

with

hello and let's access the name so

nothing

really groundbreaking then let's also

export let person is equal to

Susan and let's also set up a new

student so this will be my object and

there's going to be a type for this

student so new

student I don't have the type yet so let

me just type over here

Peter and age let's set it equal to 24

and you know what let's do set up to

type because I want to showcase how we

can nicely export type so for now let's

just go with

type

student and name is equal to a string

then age is equal to not string sorry

I'm going to go with number and then new

student is going to be type student and

now since I already have two named

exports I just want to showcase how we

can do the default one as well so we're

going to go with export default then new

student and essentially call it a day so

now I want to navigate to tutorial and

one by one let's grab all of those

values since I have the default export

I'm going to go with new student which

is coming from the actions of course we

can use a different name but I'm not

going to do that and then for the name

ones we're going to go and say hello and

also we'll set up the

person one second yep I want to save and

let me open up the tutorial over here so

these are the things we are importing

right now let's invoke say hello we're

going to go typescript okay good then

let's log the new

student and also a person just so we can

see whether we're getting the correct

values and then we'll talk about the

types and how we can export them so

hello typescript I have Peter as well as

the Susan so everything works as we

expect and as far as the types yes we

can nicely export types as well so in

here I can go with export then type

student and then back in tutorial I have

few options I can either go here with

the student notice how I'm getting right

away a nice suggestion or we can also

add over here this type again this

doesn't change anything as far as the

functionality it's just

a common approach to signal that this is

a type we're importing

so this clearly signals to me that hey

this is a type that I can use in this

file so for example I can go here with

const another student set it equal to my

student

type and let me add different values so

this will be equal to

Bob me add an equal sign over here comma

and we're also going to set up the age

of 20 three and then if I log another

student we can clearly see that we don't

have any typescript errors and then in a

console we should have the correct value

now million doll

question what is the correct quote

unquote approach should we set up the

types in a separate file and then import

it or we keep it in the file where we're

actually using the type and as always

the answer is probably not something

you're looking for it really comes down

to your preference yes definitely you

can set up over here a new file call it

types DS and then pretty much every time

you have a

type in your project set it up in the

types and then import in all the files

where you're using that value it's

definitely an option you can definitely

do do that and another approach is to

keep the type in the file where you

initially are using it and then if you

ever have a use case like in our case in

tutorial you export and then grab it in

tutorial and a common scenario is that

you initially just set up the type in

the file and then if you see that you

are reusing it all over your project

then yeah at that point it kind of makes

sense to keep it in one place since the

Imports are going to be easier you won't

have to think about well where is the

actual type located but again as always

it really comes down to your preference

all right and while we're still on a

topic of modules let's also see how

typescript treats JavaScript files so

remember at the very very beginning of

tutorial I mentioned that whenever we

work with

typescript in our case since we're

working with JavaScript files and react

files we need to stick with either do DS

extension or DSX

extension and now let's see how

typescript is going to treat the file if

it's just a JS extension so let's say

I'm going to go with source and we're

going to create the example

JS and let's go with

export some value

that is equal to some value everything

is awesome I'm just missing over here

the keyword in this case I'm going to go

with let and now if we go to tutorial

what do you think is going to happen how

do you think typescript is going to

treat this file let's go with import

some

value and it's coming

from and I don't see essentially it in

my suggestions so I can try to force it

I can say over here example JS but not

going to be successful so effectively

typescript is complaining that it

couldn't find the file now the reason

for that is because it's not a

typescript file so here's the thing

about typescript it pretty much needs to

know everything about your project and

this is something that we're actually

going to come back to when we start

working with the third party libraries

in our project essentially when we start

using the code that's coming from

somewhere else so as far as typescript

is concern no we need to set this one up

as a typescript file so then it clearly

knows well what is the shape for the

data we're getting because at the moment

typescript is like hey I don't know what

are you getting over here I have no info

on this sum value now we can force it

there's a property we can add in the

typescript config just keep in mind that

typescripts ability to infert types it's

not going to be as robust as when we're

working with the typescript file so yes

we can navigate right now to TS config

we can look for compiler options and we

can go with

allowjs and essentially we can set it

equal to true now we do need to add a

Comm over here and now everything

magically Works in our tutorial so

essentially typescript can infer that

some value is actually a string but just

be careful with such approach

effectively since we're working on a

typescript project yes we do want to

name our files

TS because then typescript is going to

know that it's a typescript file and

it's going to have the info on the shape

of the

data and if you'll just set up

JS file without making any changes to

the DS config try to run it typescript

will complain basically it's going to

say Hey listen I'm not sure what are you

exporting what's happening over here I'm

not okay with this so let me remove and

delete this import as well and with this

in place now we can move on to the next

topic and up next let's explore the

tyard options available able in

typescript basically my goal was to

gather all of our options in one place

and since we already discussed most of

them throughout the course this section

will primarily feature challenges so if

you're interested read the steps and

attempt to complete the challenge before

watching the video also for some

challenges I already provided star code

so we can spend more time on the typ

guard Concepts and we're going to start

with the good old type off typ guard and

this is going to be our star code where

we have a type it's either string number

or Boolean we assign it to a variable

and then we just invoke math. random and

then depending on the random value if

it's less than

0.33 then the value is going to be low

if it's bigger than 0.33 but less than

0.66 then it's going to be a number and

if it's actually bigger than

0.66 then it will be a bullion and our

goal is to set up a function in my case

I'm going to call this check value that

takes in one parameter value and the

type will be this value type and instead

of the function effectively we want to

check for all of these conditions for

the string number and Boolean and based

on that we want to do something again it

doesn't really matter what we do as far

as the functionality but we do want to

set up those typ guards correctly so let

me just take the star code just so we

can spend more time on the actual

function let me set it up here in

tutorial and let me start working on the

function so we want to go here with

function

then check value is we'll be looking for

the value parameter and I'll right away

set it equal to a value type now this

function is not going to return

anything at least in my setup and then

let's just set up those typ guards and

remember one of the most straightforward

type guards we have is type off and then

we have bunch of possible values so if I

go here with if then type off I'm

looking for my parameter and I set it

equal to and in here we should at least

get a list now the reason why we don't

have the list is because I have three

equal signs over here so we have this

big in fion function and you can read

the rest so let's start with the string

one over here and I guess since people

are tired with the uppercase when don't

we go with log

and value two and let's try the lower

case somewhere to lower case okay good

let's

return so we want to set up the return

here then let's check for the number and

if

we bypass both of these conditions then

logic tells us that the value is going

to be bullan so I guess you know what

order to speed this up I'll just copy

and paste in this case I'm not looking

for string we're looking for number and

then we want to go with two and fixed

and let's pass in two again we want to

return and at this point it is a Boolean

so let's go here with log and let's just

log the value so let's access the value

and let's invoke the

function so let's go with check value

and pass in the value now let me

navigate to the browser notice at this

point it's a number then I have hello

and at this point it's a Boolean and

with this in place we can move on to the

next typ guard all right and the next

typ Guard we're going to discuss is

going to be equality narrowing now don't

be scared of the fancy name essentially

is just a narrowing which occurs when we

use equality checks now I think will

right away also go with the check for

property typ guard because effectively

we'll have the same starring code so we

have these two types one is dog one is

cat and in here we have the type

property which references the actual

type and also we have the name as well

as the method which is unique to that

specific type and essentially our goal

is to come up up with a function which

is going to check for that specific type

and if it's a dog then we bark and if

it's a cat then we meow and like I

mentioned before we'll pretty much work

on both of the challenges since the

starting code is the same and we just

have multiple options how we can narrow

down one of the types so in tutorial I

want to grab this code notice how we're

using over here the Union as well so now

we have this animal which could be a dog

or a cat so now let's set up our

function which makes the sound so make

sound function we're going to go with

animal so that is going to be our

parameter and that one will be equal to

our type animal and here let's go with

animal and which property is unique well

that will be the type one correct so we

can just say well if animal type is

equal to in our case dog well what do we

want to do we're going to go with animal

and bark because we know that it's a dog

now if it's not the case we already know

that we have animal and our other option

essentially is to meow so if we go over

here and just invoke the

function depending on what we're going

to pass in that's what we're going to

get in the console now at the moment

again there's no function a over here

hopefully it's clear that effectively

we're just narrowing down the types so

this is one option we have also we can

check for

property and how does that look like

well we can go here with function then

make sound same deal animal is equal to

our animal type and then inside of the

function we want to set up if and now

we're looking for a specific

property in the type now in our case

which one is the specific one well you

can actually check for method you can

take a look whether bark exists if it is

an animal then we know that it's a dog

if not then in our case we know that

it's a cat so we're going to go with if

and then bark in so this is a keyword we

want to use in the animal well if it's

the case let's go with animal bark and

if not then we know that it's a cat so

we can run the other method let's go

with meow and let's invoke it so

effectively when we have such setup

these are the options we have either we

can check for property or a method or if

we have a property which has that unique

value for example in this case it's a

typon well then we can also use the

equality checks all right and up next we

have truthy or falsy guard and it's as

straightforward as the name suggests

essentially in here you just want to

check for truthy or falsy value in the

condition and depending on the result

just set up the functionality and as far

as the challenge we want to create a

function in my case I'm going to call

this print length we're going to be

looking for a

string parameter as far as the type

we're going to use the union type so

either it's going to be string null or

undefined and then if it's truthy if

it's a string then we just want to log

string. length if not then we'll just

say that no string was provided and then

we'll just test with few values so here

in the tutorial we want to go with

function print

length let's look for string I'm going

to go with SDR and then as far as the

type either it's going to be a string

either it will be null or we're going to

go here with undefined and if we want to

check for a valid string we simply want

to set up the if block and then pass in

the SDR so if it's truthy if there's

value in a string then we'll end up in

this if block and as far as the logic

we're going to go with s strr and then

length so at this point we know that

it's a string now if it's not the case

I'm just going to go with log and let's

just go with something generic no string

provided even though as I'm looking at

it I mean we're also going to end up

here if there's no value in the string

so technically it's not 100% correct but

let's just go with this one for now

again our main purpose was to set up the

function it inside of the function so

let's go with print length let's go with

hello over here then let's pass in the

empty string then we're going to go here

with null and after that let's pass in

pretty much nothing let's at least try

to do that now we're not going to be

able to since typescript is going to

complain but let's just pass it in just

for our reference so let's say if we

don't provide anything and also at the

very end let's go with print length and

and set up the undefined now let's

navigate to console and essentially

notice if we provide a valid string yep

the result is four so we get back this

length and if not then we just have a

list of no string provided again not

100% correct technically in here it is a

string but it's an empty one but again

these are just Minor Details the main

goal of this video was to showcase the

truthy or falsy type guard in typescript

all right and up next we have instance

off typu which is a way in typescript to

check the specific class or Constructor

function off an object at run time and

this is something we actually covered

very very recently when we talked about

type unknown so therefore in this case

again we'll have two examples we will go

back to trying and catch so we'll

reiterate pretty much everything we

learned in the type unknown video and

also we'll work on the another example

where we'll check for the date so first

let's just reiterate that if we have try

and catch this error is unknown so even

though we have over here for sure throw

new error and if I pass in the message

typescript will complain if we'll just

go with error.

message because there's also

a possibility for different type of

error

essentially we might have an error which

is not the instance of the error class

so therefore if we do want to access the

message first we want to go with error

and then instance off and we're looking

for our error class so if it's the

instance yes then we know that there is

that message if not well then we simply

want to log something some kind of

hardcoded message so let's go here with

log and then let's provide some kind of

string and we're looking for error

object and now we just want to render I

guess the error message so error that

message so now we can access it if not

well then let's simply log something

else we'll just go with unknown

error error and do dot dot again if we

navigate to the browser if everything is

correct we should have this one over

here why well because at the moment in

Tri block I have try new error now if

I'm going to comment this one out or

simply type above and say throw and some

error now I should have unknown error in

the console so again this is something

we covered pretty much few videos ago

now also we can use such setup to check

for date so we can check whether the

input we're passing in is a string or

it's actually the instance of the date

object so let's set up our function

we're going to go with check

input and in

here the variable name is going to be

input basically the parameter name and

then either it's going to be date or

it's going to be a string now from this

function we want to return a string and

now we want to check whether the input

is the instance of the data object if

it's the case then we want to turn it

into a string now if it's not the case

if it's simply a string then we want to

return the input so let's go with input

instance off then data object here and

then let's use input since this is a

date right now we have access to all of

these methods we're looking for get full

year let's invoke this one and we want

to turn it into a string so notice if I

just return this one typescript

immediately complains because this will

be a

but we said that we want to return a

string so let's invoke this two string

so now typescript is not complaining and

if it's not the case if it's not the

instance of the date well then I don't

need to do these acrobatics I can simply

return the input so now let's construct

two variables we're going to go check

input in here let's just pass in new

date and also we're going to go with

some random values as well random

and we'll set it equal to check input

and let's just pass in some kind of

string so

2020 the best year

ever of course in the air quotes and

let's pass in some random date then

let's log both of these values we're

going to go over here with year and

random I'm not even sure whether we are

really interested in the console but

let's just log it and notice essentially

both of them are strings and again the

instance of typ guard is a Nifty way for

us to check in typescript whether the

object is an instance of a class or

created by the Constructor function if

it's the case it's going to return true

if not it's going to return

false all right and up next let's

discuss type predicate function which is

a special kind of function

that not only returns true or false but

also we can narrow down the type and

again this should be a refresher because

we did discuss type predicate previously

as far as the star code let's just grab

this one and then we'll go over the

challenge so here in tutorial I have two

types I have the student one as well as

the user notice this property is the

same it's a string and the only

difference well they have different

methods so one is study and the other

one is login then I use the type Union

to create type person which can be

either the student or the user and then

again I go with my math. random if it's

bigger than

0.5 then I'll return one if not well

then I'll return another one so either

this is going to be a student or a user

and effectively what we want to do is

set up our type predicate function where

not only we check for specific type but

we also want to help typescript by

narrowing down the type uh in my case

I'm going to show you two options how we

can check for specific type but feel

free to use whichever makes the most

sense to you and then after that we want

to use if else essentially run our type

predicate and if it's true we want to

invoke one of the methods so let's say

in my case I'm going to be checking for

student if not then I'm going to invoke

login which is for the user so right

after the person I'm going to go with

function is student at least in my case

I'm going to be checking for student

again this is totally up to you you can

check for user as well now I'm going to

be expecting a person which again can be

either of them for now I'm not going to

set up the return type and as far as our

options well we can use the in operator

something we talked about literally few

videos ago where again we're looking for

something unique in this case either

it's going to be study or a login and we

just go with the method name then in and

then the person since that's our

parameter or we can also use the type

assertion which where we assert that

person is going to be a student then we

invoke the study method and then we

check whether it's defined or not so

again this part is totally up to you for

now again we don't have any returns I

just want to showcase that if we go here

with return and then study again our

method in person this will return either

true or false so

either this method is in the type or not

now if it's the case then we want to go

with person

is the student correct because at that

point that script knows for

sure

that the instance is the type of student

and if that's the case then we can use

the study method now alternatively we

can use this approach where we go to

return Then person and we assert that

it's a

student now what is the method student

has it has the steud one but again just

because we are asserting doesn't

magically make this person to be a

student and therefore in here we still

check we say okay we assert that person

is a student we know that there is a

study property but it also can be

undefined so it's only a student if it's

not undefined

like so so those are the two options you

can use over here and now let's set up

the if blog let's say well if it's a

student then let's pass in the person

what do we do at next well then we can

use essentially our method correct and

if it's not what options we have well

then it's a user correct so we go here

with person and then log in and also

invoke it again a very fancy name type

iate effectively just remember the is

keyword and remember the fact that not

only we're trying

to check for a specific type but we're

also helping typescript to narrow down

that type okay and before we move on to

the next topic I also quickly want to

show you one

gotcha and this involves type never now

technically this video is optional if

you're not interested you can just move

on to the next video but I simply want

to showcase that if we hardcode the

person to be a specific type typescript

is going to yell at us so in here yes we

are setting up that person randomly

correct so we have our random person and

pretty much depending on the value well

we either return a student or a user now

if I set up my person differently let's

say if I comment this one out again I'm

going to go with person I'll say that

this type is actually a person and then

I'll hard code so I'll say name is equal

to Anna and then since I'm creating a

student I'm going to set up my study

method so I'll come up with my function

and I believe it doesn't return anything

so I'll just go with log and study dot

do dot okay let me fix the typos and all

that so now I have this person but I'm

hardcoding this is not any more random

notice TPT essentially right away yells

at me says well there's no way this

person can be a user the other type why

well because you hardcoded to be a

student so yeah I can still check

whether the person is

student so type pred code still works

but in the lse block you'll notice that

person is

never and this brings me back to the

point that I was making in the type

never

video essentially if you have the

scenario where type is equal to never

you'll just have to go back to the

initial place where you're setting up

the variable and also start checking

your conditions because effectively in

here typescript just says Hey listen

there's no way that person can be a type

user because you hardcoded to be a type

student now what's interesting if I

change this around to a

login now the person is actually a user

correct so now I'm hardcoding to be a

user so I have my type predic cut I

check in my condition it's not the case

and now we can successfully get to else

but if I hardcode my person to be a

student then there's no way for me to

get to this pulse block hopefully it's

clear and now we can move on to the next

topic all right and up next let's

discuss discriminated unions and also

let's recall how we can set up the

exhausting check using type never now

again I I know that the name

discriminated Union most likely sounds

pretty scary but essentially it's just

going to be a

property which has a literal value now

as far as the star code this is what we

have over here so we have two types one

is going to be increment action second

one will be decrement action both of

them taking the number the amount time

stamp which is going to be a number

again this is totally random and the

same goes for user string this is

totally random and then we have a type

by the name of action where I use the

union type and I just use both of these

types here so either it's going to be

increment or decrement and then I will

set up a reducer function which is

looking for two things it's looking for

the state so again this is just going to

be some random number and also the

action so what do we want to do do we

want to increase the number or we want

to decrease so let's start setting up

and in a process you'll see why we need

the fancy discriminated unions which

again is just a property with a string

value so for S let's go here with new

state and you know what I haven't set up

the functions so maybe let's start with

this one so we have a

function looking for state which will be

a number so some kind of hardcoded

number and then also the action so

whether we want to increase or decrease

and by how much this is the amount over

here so if we want to increase then byy

this amount and the same goes for

decrease now I'm not going to set up

again anything as far as the

functionality I simply we want to go

with

reducer that's the function and of

course I forgot to add the name over

here my bad so we're looking for

reducer then as far as the initial value

again we're just hardcoding something

random so I'm going to go here with 15

and then when it comes to action well

now I'm going to pass in the object so

either it's going to be increment or

decrement and in this case I'm going to

hard code that user value will be John

we don't have the type yet so let's just

go here with amount of five and then

time stamp well let's set up 1 2 3 4 5

six or something along those lines and

now let's discuss why do we need the

discriminated unions in the first place

well we have two types

and how are we going to check for

specific type I mean we canot use type

off we cannot use in we cannot use I

mean instance off or any of the things

that we covered previously why well

because pretty much they're the same

correct now they do have different

meaning one is going to increase this

state over here and the other one is

going to decrease but in the reducer how

I'm going to check for that action this

is where the discriminated unions come

into play where

we'll have this unique literal value how

is that going to look like we'll

navigate back to increment action and

yes effectively you'll just add here

whatever property name you want in my

case it's going to be a type and it's

going to be equal to increment and now

we want to do the same thing for

decrement so instead of increment we

want to go with decrement so now in the

reducer we want to set up

a switch statement where we're going to

check for the type if it's increment

then we'll increase if decrement then we

decrease and also let's just recap how

we can set up our default case with the

help of type never now typescript is

complaining because I'm not providing a

typ over here so we do need to go with

one of them in this case I'm just going

to going to go with the increment again

it doesn't really matter

since our main focus is on this logic

here in the reducer so first let's set

up the switch one and we're going to be

looking for Action type that's the

property we're interested because it's

Unique to each type over here and again

if we have 10 types yeah we'll pretty

much have to set up the type for all of

them and provide that unique value then

we want to go with case and this case

I'm going to go with increment and as

far as what do I want to return from the

function well let's go with number so

we're going to go with that initial

value basically a state and we'll add

action Dot and the amount that I'm

passing in now we want to do the same

thing for the decrement correct so let's

just change it around and again let's

just recall the issue with the setup if

we add some other type to this action

well it's going to fail silently correct

and therefore we want to set up the

default case and we want to assign the

action to some variable which is type

never because in that case if there's

some other type over here it will

immediately be assigned to that variable

and we cannot assign to type never so

let's just go over here say

default that's going to be our default

case let's also throw I guess quite

typical scenario so throw new error and

then I'm going to set up the template

string and in here essentially let's set

up

unexpected for some reason this is the

biggest challenge as far as the spelling

unexpected action over here type will be

equal to never and we'll assign it to an

action so if actually action is never if

we have handled all the possible cases

we're good to go but if there's going to

be some additional case and we're not

handling right away typescript is going

to yell and in here let's just type

unexpected action and then let's access

the unexpected action again the point

really here is not to run the code I

mean we're mostly focusing just on the

logic over here in the redu sh so this

is how we can set up the discriminated

unions and exhaustive check using the

never type in typescript okay and we

have successfully arrived at the most

complex and confusing Topic in

typescript which is none other than the

generics

in short generics allow us to write for

example functions with any data type and

you can think of generics as a variable

for types now I'm not going to Sugar Cod

it it's not an easy topic the good news

is though that most likely in the

beginning at least based on my

experience you'll primarily use generic

functions or interfaces created by

somebody else whether it be the creators

of typescript or developers of some

third party library and in that case

you'll only need to remember one concept

every time you see those funny looking

angle brackets think generics and let's

begin by taking a closer look at the

arrays in typescript so at this point in

tutorial we should be already familiar

with this syntax so we have three

variables the values are arrays and here

we just say well what is the type for

the array and as we're looking at this

code and we're just focusing on

typescript so please don't tell me that

the answer here is the keyword let as

you're looking at this code what is the

one thing that doesn't

change so what is the one thing that

stays the same and it's kind of pretty

obvious but I do want to start from this

point and the answer is following notice

how the type is changing here all the

time but we're always always getting

this array now of course we can make

this complex we can provide our own type

we can provide the union type whatever

that doesn't change the main idea we're

always always getting back this array

and not only that we can pretty much

pass here whatever we want as far as the

type correct so it still needs to make

sense as far as type and we'll always

get back the array so it's not like I

need to go somewhere and look for string

array no I don't have such type I

literally just have this one universal

one that I can use because if you think

about it how difficult it would be

that not only we need to remember but

also to construct such types let's say

we'll need to have one numbers array

type then one Boolean one and I can go

on and on and on and

on and actually we can examine what type

are we getting back over here so let me

remove this silly text and now let me

right click then we want to go to type

definitions and yes I know we haven't

covered the Declarations yet don't worry

all of that is coming up and you know

what I'll actually pick the third one

because it's going to be easier for me

to show you so let's go here to type

definition and then we're looking for

this declaration one so we're looking

for lib es5 D DS again we haven't

covered them how we have access to them

and all that all of that is coming up

for now but just focus on this code so

notice we have this interface again

something we should be already familiar

with remember we use it to provide shape

of an object the name here is an array

and check it out we have the funny

looking angle brackets and inside of it

we have this T now right away I want to

mention T is convention you can call

this shake and bake you will see that in

a second once we set up our own generic

interface or function or whatever

basically this

represents the notion that this type can

be anything so I can pass here the

string number Boolean my own type you

name it and every time not only I'm

going to get back the array with that

specific type I'll also get all of the

properties and methods that we know

already exist on array so what am I

talking about well we know that length

is part of the array correct we can just

call array. length and we're good to go

so notice we have over here this method

so we can definitely use it and then

let's keep on moving and we'll see again

all of the functions we already familiar

with but here's the kicker for example

pop now if you're not familiar this

essentially is a function which removes

the last element from the array and

returns it but now notice what is the

return here specified for the pop it's

not string number or Boolean or your own

no it's basically this D it's basically

this generic so whatever I pass in

whatever array I

construct well I want to remove that

last type

correct I'm not saying hey this is the

array of strings and now I need to call

specific method to remove the string no

basically whatever type we use to set up

that array well that's the same type we

remove and

notice how essentially

we're saving bunch of the code because

imagine if you would have to set up such

interface pretty much for any type that

we can pass in the array I mean you

would go most likely insane so that's

why we use this variable where we say

okay you can pass in any type and it's

going to get treated the same way we'll

create the array the same way we can you

call the methods the same way so so none

of that changes so whatever type we pass

in well that's the type we're going to

use to operate so hopefully again this

is clear that it definitely makes sense

in a lot of instances to set up the

generic one because you don't want to

set up essentially the interface for

every possible type that you can pass

intoa and now knowing this we can

actually take a look at the second

approach we have to construct the arrays

now I can tell you right away that just

because we know the generics you won't

have to use the syntax so you can still

use this I would say more userfriendly

syntax but I do want to showcase that

since this interface is an array we also

have this option so now let me comment I

guess these ones out you know what let

let me start everything from scratch so

I want to go here with let and again I'm

going to call this array one and and

then as far as the type sorry I'm not

going to go with string I will go with

array and then let's pass in the string

and now as far as the result well that

one is actually exactly the same so I'm

just saying yeah it's going to be an

array of

strings and

again this doesn't change the only thing

that's going to

change the type that we're passing in so

if we pass in the string and of course

course we'll get back array of strings

as well as all the methods that we can

call so if I call the pop on this one on

array one guess what it's going to

remove the last item and the type is

going to be string and of course we can

repeat the same for number and bullion

and with this in place now we can move

on to the next topic all right and once

we're familiar with the main Concepts

let's construct our own let's start easy

let's just go with the function as well

as the interface

so here's the goal we want to create a

function which is going to take any type

and return the same type so one approach

could be following we can go with

function then let me go with create

string as far as the argument I'm going

to call this string basically I'll give

it a type string it returns a string and

then from the function we return the

argument now

everything is awesome but we pretty much

need to return the same function for any

type so we need to create one for the

number for Boolean and rest of them now

I'm not going to create function for all

of the types but you know what let me

just Showcase with a number so let's say

if from this function we want to return

a number this is what we'll need to do

and as you can see this gets annoying

pretty fast correct and we only have two

types so this is what I was mentioning

in the previous video imagine that array

interface if it's not a generic that

pretty much you'll need to copy and

paste and everywhere where you have a

string you'll have to change it to

number and Boolean and then rest of the

types so what's the solution well this

is where we use the

generic I will leave this one for your

reference or you know what actually you

have it going read me my bad let's start

from the scratch I think it's going to

be better we're going to go with

function then let's call this something

generic and I think generic function is

good

enough and we will set up the parameter

we will set up the

logic now I want to set up the variable

for my type so instead of hard coding

instead of number and string I'll say it

can be any type and both my argument as

well as what I'm returning are going to

be that type so we go here with this

angle bracket like I said you can call

this shake and bake just make sure you

use the same name and again the

convention is just to go with d which

stands for type so we go here with t

then we say that yeah argument is

actually going to be this type so I'm

not going to say that it's a string

number whatever no whatever type we have

over here and as far as the return will

also go with the T this is what I'm

returning from this function and now we

just need to set up the logic where we

return the argument so now we

can go here and set up some string value

set it equal to generic function then

since I'm creating a string value this

is the type I want to pass in and then I

just want to provide a string let's save

this and now I can do the same thing for

the number so instead of string we're

going to go with number and instead of

type string will set up the number now

it does need to make sense as far as the

argument so it's not like I'll randomly

pass in the string as you can see

typescript is complaining and we set up

over here the number so now we can use

this function with any type even the

ones that we set up ourselves so this is

not limited anymore to one specific type

this right now is generic function where

we can pass in any type and we'll get

back the same type and while we're on

topic let's also take a look at the

interface so I'm going to go with

interface and let me right away call

this

generic interface same deal if we want

to set up a generic one we already know

that we need to go with angle brackets

let me stick with convention with the T

and then there's going to be a value

property the type will be whatever we're

setting up over here SD that's why they

need to match and let's also set up the

get value

function which is not going to take any

parameters but it will return the same

type and now let's create a new instance

I'm going to call this generic string

which is somewhat funny but let's just

stick with that one since I have that in

a read me so we're going to go with

generic string we go here with generic

interface we say that yep as far as the

type it's actually going to be a string

and now inside of our instance of course

we need to follow the same rules so the

value I'm going to be setting up has to

be a string so we'll go here with hello

world and then as far as get value

one well let's just return this do value

return this do value let's save it and

once I save I have right now the string

instance from my generic interface so

this is how we can construct our own

generic functions as well as generic

interfaces all right and before we start

working on the more complex examples I

do you want to showcase something most

likely as you're looking at these first

few examples you're like I mean this is

ridiculous what is the actual need for

such functions I mean I do understand

yeah there's angle brackets yeah I can

use this T and it's going to work with

any type but in reality this is just

silly okay hold that thought and let's

just set up a a sync function and

remember in JavaScript

what do async functions return they

return a promise so let's go here with

async call this function I'm going to go

with some funk for now let's not worry

about the return or you know what no

let's set it equal to a string do

definitely want to showcase something so

we right away have the error this is

something we're going to deal with for

now let's just return and hello world so

technically it's kind of correct we're

return a string so what is typescript

complaining well

again same functions return what they

return a promise so now let's do the

same thing like we did with the arrays

let's look at the type that we're

getting back and hopefully in the

process you'll see that even though this

might look somewhat silly essentially

this is the foundation that you'll see

over and over and over in document ation

so if I'm going to go here with

result and some funk and we take a look

at the result I mean it says that it's a

string but we clearly have this issue

over here and notice now we have this

the return type of a sync function or

method must be the global promise again

funny looking angle bracket type did you

mean to write promise and hm interesting

we actually have the generic again so

you know what let me remove the return

type for now I'll rely on typescript to

infer a type and now let's click on the

result and type

definition and same deal noce we have

over here this

interface the name is promise and again

it's a generic and yes it has a little

bit more code but not just the general

idea effectively we just get back this

promise and in there we have the type so

the point is that every time we have

this async function we do need to set up

promise as a return type and we just

need to remember that it's a generic so

instead of typing string like I was

doing before we just go with okay we're

returning a promise but since it's a

generic we need to specify the type in

the angle brackets so again the main

point is that yes I know that this might

look silly but keep in mind that this is

going to be the foundation that you see

in documentation as silly as it looks it

actually handles all of the cases that

we're interested because in here I can

return whichever type I need in that

particular instance and I simply just

need to provide the value over here in

the angle bracket so let's say if I'm

going to go with 234 or whatever number

then is going to complain so now I just

need to go over here and say yeah I will

return a promise because it's a sync

function but the type in this case is

going to be a number so yes even

though our first two examples might look

super silly

they use the same concept that you're

going to see later in declaration files

and with this in place now we can move

on to the next topic all right and once

we are familiar with the fundamentals of

generics let's work on a tiny challenge

where we want to set up a function in my

case I'm going to call this create array

which takes in two things it takes the

number length so that just controls the

length of the array so if I pass here

three then I'm going to have three items

if I have pass here 15 then obviously

it's going to be 15 and then the second

thing is going to be the actual value so

if I pass in the string then I should be

getting back the array of strings if

it's going to be number then it's going

to be an array of numbers and hopefully

you see where I'm going with this and I

guess let's start

Again by hardcoding hopefully in the

process we'll

see why we want to use generics but

first let's create a function I'm going

to go with

generate string array like I said we're

looking for two things length is going

to be the length of an array and also

well what is the actual value and as far

as the type I'm going to go with string

now from this function since I'm taking

in the string type I want to return a

string and array now when it comes to

logic I want to create the result

variable this will actually be string

and array and for now it's just going to

be empty array but yes we're going to

store over here the strings okay good

then let's assign result to array so

again we can use our object in there

first we want to pass in the length so

how long is going to be the array how

many items we're going to have over

there and then let's just call the fill

method so pretty straightforward

whatever value we pass over here we'll

add to our result so we'll call fill and

we'll pass in the value and then from

this function since I want to get the

array of strings let's just go the

return and result let's save it and

again everything is awesome but I need

also the same array for numbers booleans

or any other type so now we just need to

make this function generic or you know

what let me just quickly showus that the

code actually works so generate string

array how many items I don't know let's

go with six because I have the example

of three so you probably don't believe

me let me go over here and notice

everything works so I get back my array

it's typ string and I have six items

okay beautiful so now how we can make

this function generic and again most of

the logic is actually going to be the

same the only difference everywhere

where we have the string we just want to

convert it to a generic we want to

convert it to that variable and as a

result we'll be able to pass pretty much

any type

so let me copy and paste instead of

generate string array we'll just call

this create array create array length

stays the same but this one actually is

going to be equal to at and now we want

to set up that angle bracket so again we

set up this variable for a type and we

pass here DT so now everywhere where we

want to reference the type we'll use the

T instead so here instead of string

instead of hardcoding that we'll go with

array and pass in the T then instead of

strings we're going to say that yeah the

result is going to be just an empty

array of this specific type this doesn't

change this doesn't change now we just

want to invoke it and we'll do the same

thing like in the read me we're going to

go with strings then create

array we want to provide string over

here here and far as the value let's go

10 the more the better I

guess let's copy and paste and let's

call this

numbers so

numbers this will be a

number uh let's go with

15 and as far as the value I'm going to

go with 100 so now we just want to log

both of these values array of numbers

and strings

strings let me move this one

up just because don't ask me why and if

everything is correct this is the result

we should see in the console so this is

how we can create a function which takes

any type and returns an array with

specific length of that particular type

all right and up next let's see how we

can set up multiple variable types and

in my case I'm going to use the function

example so we want to set up a function

called pair which takes in two

parameters however the type is not going

to be the same and then from the

function we just return both of those

parameters but again we need to return

the same types so let's go here with

function again the name will be pair we

start with our good old T so we already

know that one but if we have multiple

variables like this we just add a comma

and then provide the value again it's a

convention to go with du and then if you

have more parameters just follow the

logic over here but you can name them of

course differently as well then we're

going to set up our param I guess one so

this one will be equal to T and and then

param 2 is going to be equal to U like I

said from this function I want to return

an array and I want to keep the same

types so this will be equal to D and U

and let's just set up the logic where we

have Pam one comma and then Pam 2 so now

let's invoke it and if everything is

correct we should get the correct result

so we're going to go with the result

that one is equal to pair

and then I'm going to go with number and

a

string let's go with one two three and

hello and check it out typescript is not

complaining so if you have more variable

types add a comma and then the common

approach is to go with you and then rest

of the letters that follow you if you

have more parameters or you can come up

with your own names just make sure you

use the same name in the parameters as

well as the function logic and up next

let me quickly show you that t script

can still infer the type even if we

don't provide the types here in the

angle brackets but just like before we

need to be careful yes if you're

expecting to get back the number and a

string everything is awesome but if by

mistake you pass in some other type it's

not like typescript can magically figure

this out so therefore if you don't pass

in the types You're Expecting just make

sure that you pass in the correct values

hopefully that is clear and as aen this

is something that we're going to see

later when we start working with react

where use State hook actually is a

generic which again if we think about it

kind of makes sense right I

mean we can pass in string into use

state

same how we can pass in the array so

this used State hook needs to accept

whatever value we pass in whether that

is a string number all the way to array

of

objects and essentially since it's a

generic we can technically bypass the

angle brackets so let's say if it's a

string I just let typescript to infer

that yes for sure it's going to be a

string since I'm passing in the empty

string but for example when we're going

to be setting up the Rays typescript is

going to complain and at that point

we'll need to specifically let

typescript know hey is it going to be an

array of strings numbers and in this

case I'm just coming up with some fake

product type so hopefully that is clear

yes typescript can still infer the type

just be

mindful when you use such a pro approach

and also I want to show you how we can

set up the constraint on a type

essentially I can limit the type options

I can pass in so let's imagine this I

have a function of process value

function process value and in here I

have my generic T but I only want to

limit this to a string so the keyword

we're looking for is extends and then in

here we pass in the specific type now in

the following video I'll show you a

different example so don't think we can

only use it here with primitive types

but let's just start nice and easy so

we're going to go over here with the

string then we want to set up a

parameter again I'm going to say that

it's equal to at and you know what let's

say that we're also going to return it

so in here let's log it let's say value

and let's also return the value let me

save it let me call Process value now in

this case I'm just going to infert the

type and I'm going to say hello and as

you're looking at it you're like well I

mean at this point we can simply set up

a function without the generic correct

so I can simply say that yeah I'm going

to be passing in the string and I'm

expecting a string back and you're 100%

correct so with this particular example

I mean there is no real benefit of

setting up the type and then extending

it only down to a string but again it is

a option and in a following video you'll

see a more complex example where

actually it definitely makes sense now

we can also use the union type so

effectively I can go with string or

number and at this point if I call in

process value I'm able to pass in the

number as well so for example I can go

with 12 now if I'm going to go with

process value and then pass in I don't

know true then of course typescript is

going to complain because we can only

pass in string or number in this generic

function and once we're familiar with

the extends keyword now let's see a more

complex example where we have our own

types so let's imagine the scenario

where I have type car two properties

branded model both of them strings then

I create the instance same with product

only in this case the properties are

name and price and I have string and

number again I create the instance and

the same with students so the properties

is the same the first one name it's a

string but then the second one is age

and in here I want to come up with a

function I guess I'm going to go with

print name because why not where I just

want to access the name prop property so

let's go with our function print name

then let's provide the type the generic

in this case we're going to say that

input is also going to be D and we're

not going to return it so I'm going to

go with void now even if we just try to

conso log input that name typescript is

going to complain why because it has no

guarantee that there will be that name

properly so in this scenario we're not

going to extend to a string we actually

need to look for the types which have

that name property correct and in our

case we can either go with the student

or with the product we just set up over

here extends and we go with student so

just like before with string number

Boolean or whatever we can use our own

types as well so now if I go and invoke

the print name in here and if I'm going

to pass in the student everything is

going to work now it's going to fail if

I pass in the product even though it has

the name correct let's try it out so I'm

going to copy and paste and once we

invoke the not print name print name

sorry we're looking for a product of

course typescript is going to complain

because the type is product in this case

so yes we can still use over here the

union type and passing the product but

there's actually a better way because if

we think about it what are we going to

do now we'll look for all of the types

where we have the name and then

essentially just use the union type and

add it to extend I mean technically it's

an option but like I mentioned there's

actually a better way and that better

way is that we can set up an object we

can set which property we're looking for

and then we can pass here in the extends

now we can set it up as a separate

variable or we can pass here directly so

instead of passing in my student or

product types I can simply set up an

object and I can say Hey listen I'm

looking for name property and it has to

be a string so now that script is smart

where it says okay so student yeah it

does have a name so everything is going

to be fine same with the product but if

I'm going to try to call it with a car

it's not going to work because there is

no such property so if I pass in this

instance notice entually it complains

that the name property is missing in the

car so this is an interesting way how we

can use extends not only with a

primitive type or our own custom type

but also we can simply narrow down to

the shape that we are expecting okay and

at the very end of generics let me show

you how to set up default type just

please keep in mind that it's not going

to be super useful in our examples since

we're hardcoding all of our data anyway

basically they're going to be far more

useful when we don't know what is going

to be the shape of our data so let's

imagine we have

interface it's going to be a generic and

I'm going to call this store data I'm

going to say that I'm expecting T and

then inside of it there's going to be a

data and it's going to be equal to an

array of types so whatever we pass over

here then let's set up store numbers so

store numbers and first let's set up the

type so we go with store data then

number and then we set it equal to data

and in here since I want to store

numbers I'm just going to go with one

two three and four okay so this works

but what if let's say I have some random

stuff what if I don't know what I'm

going to have in the array well let's

try it out so we're going to go with

random stuff set it equal to store

data for now we're not going to pass

anything in we're going to go with data

and then we'll set up some random stuff

so I'm going to go with my string over

here as well as the number now store

data is expecting the type so at the

moment essentially we have two options

either we set up over here the default

one then we won't get the error over

here or since let's say I not sure what

data I'm expecting back technically I

can hardcode here any I can say yeah I

mean I'm not sure what values I'm going

to have in this array so I'm just going

to go with type any now if we want to

bypass

this essentially passing in any if we

don't know what data we're expecting we

can simply set D equal to any or any

other default type as a side note you

can go here for example with string or

whatever is just somewhat common to see

and as default type and in that case we

don't need to even provide it so if I

don't provide the type then right away

typescript is going to use any as my

default one again kind of hard to see

over here because we can clearly see

basically what we have in Array but just

to Showcase that I'm not making this up

let me grab the example from the readme

so if you're interested that you can

also copy and paste now there might be

some errors since I don't have those

values over here don't worry about it

too much I just mainly want to showcase

some

stuff most likely you're familiar with

the library called axios which is super

popular to make HTTP requests and

normally the syntax is following where

we go with AOS then the method Now by

default it's get but in here I hardcoded

get as well and we pass it the URL and

the data is

located in the object in data property

now if we take a look at their

documentation we can actually see that

get is a generic what does that mean

well it's looking for the type but if

it's not passed in over here it uses any

so if let's say you just called axios

doget it's going to set data as any so

whatever we're getting back and we can

actually see that if we continue

inspecting the documentation notice

there's also a second one which is r and

that one by default is equal to aio's

response and it uses the type we pass in

so essentially this is another generic

interface which is used as a second type

over here and essentially it uses the T

that we pass in now if we take a look at

the axio response in our generic one we

can see that we're getting back this

data and this is set equal to T but

again the default value is any so for

example if we don't

provide any info on a type it's going to

be equal to any because that's the

default as we can see it's used over

here it's passed down to AIO response

and the same deal in in the interface

now if we set up the angle brackets and

specifically say that Hey listen I'm

fetching this data but I know that

structure is going to be following I'm

going to get back the array of object

and in there I'm going to have name

which is going to be a string in that

case this data will have this shape so

if we

provide essentially a shape that we're

expecting then the Ste becomes that

shape and goes all the way down to data

now if not then they use the default

parameter and essentially set equal to

any now I know it's a lot of code in

here a lot of angle brackets and that

but hopefully it's clear now we can

nicely use type any if we don't know

what shape we're getting back because

again think about it this is an HTTP

request so the shape can literally be

anything and therefore the default one

is any and then if we provide specific

shape well that's the shape we're going

to have here in this data property okay

and while we're still on a topic of HTTP

let's also see how we can fetch data

with typescript now normally I use axos

library with react query simply because

the setup is super straightforward and

react query is really good at inferring

the types but let's start nice and easy

and cover up the straightup pitch API

first and also keep in mind that in this

example we'll just log the result so we

won't set any state or display pretty

much anything in a browser we'll just

check for correct results in developer

tools all of that is coming up just be

patient and wait for the react part of

the course now also you will need the

URL so in the read me I provided a URL

back to my server where we can just

fetch some random tours we were using

this one in my react

course basically build one of the

projects so this is totally up to you if

you want to use this URL feel free to do

so if not if you have some other URL you

you can of course use that as well and

for now we'll just simply set up a fetch

function we will log the result we'll

see the issue if we don't have any type

and then in the following video we'll

have a challenge where you'll have to

set up the type and proper returns and

all that cool stuff so for now let me

just grab I guess the URL so we're

looking for this one over here and we

want to come up with a function so in my

case I'm going to go with

sync function let's call this fetch data

it's going to be looking for URL it will

be a string over here for now no returns

we just want to set up the TR catch

since we have a sync operation it's

always a good start now in here let's go

with response so this one will be equal

to a weight fetch we pass in the URL so

notice how we can right away start using

Fetch and actually we'll cover that in I

believe two three videos how come we

have access to this function without any

issues and typescript doesn't complain

and fetch has this interesting setup

where it doesn't treat for example 404

errors as errors it only treats the

network errors as errors basically if

you'll have 404 over here it's not going

to come up in the catch block so we will

do a manual check where else say if

response.

okay is not set well then I'll throw my

own error again this is just an extra

check we need to do with fetch for

example you don't need to do that with

axio so go row new error then let's set

up the template string we go with HTTP

error and the status here let's go with

status and we're going to set it equal

to a variable

let me access that we're going to go

response that status so now we're

checking even if we'll have 404 error it

will actually trigger the error and we

will return whatever we have in catch

block and now let's access the data

again we're looking for the array of

objects that's what we have here and you

can definitely see that if you navigate

to this URL in the browser

and we want to set up another

await let's go with the response and

Json let's invoke that and at the very

end of the tri block let's go with

return data now in the catch block let's

right away construct the message so I'm

going to go with error message and this

one will be equal to ter operator where

I'll check if the error is instance of

error well then I'll will set the error

message variable equal to error. message

since I know that the property is going

to be there if not then I'll just go

with something generic there was an

error so let's set this one up and then

let's log just so we can see what's

happening we're going to go with error

message here and then at the very end of

the catch block we want to return empty

array so if we're not able to get all of

the tours will return

MTR now I guess for now let's just log

what we have in the data and let's

invoke the fetch data fetch data let's

pass in the URL if everything is correct

in the console we should see this array

of objects and if I go over here and

mess with the URL since I have this

check over here now the response is not

going to be okay and I can clearly see

that over here so we're nicely throwing

the error as well and this is going to

be my error message so this works now

where is the issue well let's go over

here set the tours away to TS so now I'm

essentially assigning this to some kind

of variable and notice something

interesting what is the type well it's

any because typescript doesn't know what

I'm getting back so so yeah I was able

to fetch data I have access to it I have

no issues but this is equal to type any

now why is that such an issue well let's

try doing this let's go towards map we

know that we're iterating over correct

our array and we should have access to

each and every object over there but if

I type tour check it out typescript

immediately complains says okay I have

no info on this this is type any so how

am I supposed to know what is this tour

so we're not getting any suggestions

we're not getting Auto completions

anything like that so yeah I can set

this equal to tour and and

then go with tour. name but I mean this

is not going to be sustainable in the

long run so yeah I can nicely see

everything in browser's console but

since we're working with typescript we

will have to figure out how to provide

the shape of our data to typescript so

typescript knows that Hey listen this

tours is going to be an array of Tours

where I have following properties so I

have ID name info and rest of them and

this is something that we're going to do

in the next video as a challenge all

right and once we see the issue now

let's fix it how well we're working with

typescript so we need to provide the

shape and set up the correct return type

for our fetch data and once we do that

typescript is going to know what we have

there and then we'll have Auto

completion suggestions and all that cool

stuff so here's the

challenge set up to type a hint you can

use the URL as your reference and also

set up a proper return type for the

fetch data again hint remember that it's

a promise correct because it's a sync so

first let me navigate to the browser and

I can see that essentially each and

every object is going to have ID name

info image and price and guess what it's

pretty straightforward all of them are

strings so now I just want to navigate

back to

tutorial somewhere over here set up my

type I'm going to go with type and name

is up to you in my case I'm going to go

with tool

ID is going to be equal to

string then I have the same for name

info image and price so you know what

let me just copy and paste hopefully

it's going to be faster in the long run

so we have info here then we have image

and at the end we also have the price

let's save this and there's two places

where we want to set up this type so

first we want to set it here where we

have the return and I'm also going to

set it over here where I have the data

so I'm going to say that I'm expecting

from this. Json back my array and it's

going to be an array of Tours and the

same over here for my fetch data I'm

going to go with my return and remember

this is a sync correct so what do we

need to pass in a promise promis is what

it's a generic so we go over here with

tour and then we pass here the array as

well now don't worry if it's empty it's

still technically going to match

whatever we have in our return and now

we don't want to set this as any of

course we can actually go back and we'll

nicely see that this is a tour why is

that super beneficial because check it

out if I'm going to go here with log and

tour dot notice I have all of these

properties right away avail ailable I

can go with name save it again the

result in the browser is not going to

change but essentially this is just a

type Safe Way how we can fetch data

where we come up with the type we set up

proper return and after that can start

using this data in a type Safe Way in

our project all right and the moment we

feel good about ourselves that we have

nicely provided the type and Everything

is Awesome we can start using in our

project let me throw you a m grenade so

what do you think is going to happen if

I'm going to remove some Properties or

I'm going to add some extra ones so

let's say if I'm going to go with

something and then I'm going to set it

equal to a bullion what do you think is

going to happen you think I'll have

access to it you think typescript is

going to complain and I guess you can

clearly see that typescript is is not

complaining and actually if I go over

here technically I can even select it

but what is the result I'm getting back

undefined so here's the

kicker yes this is definitely something

we want to do we do want to provide a

correct shape to the typescript but

there's no way for typescript to check

this at

runtime so yes this is super useful for

us to later use in our code you saw

previously what happens if we don't do

that then basically typescript thinks

it's any but also just because we set up

this type over here at build time it

doesn't 100% guarantee that at run time

we'll get the correct results because

this is just build time in here we're

saying yeah this is going to be my shape

so I can type here whatever I want and

typescript is going to be like Hey

listen

you told me that this promise is going

to return the array of Tours and this is

going to be the shape for the tour but

what if the something is actually not

there I mean there's no way for

typescript to check that and therefore

in the following video we'll take a look

how we can do the runtime checks with

the help of extra Library by the name of

Zod okay and up next let's see how we

can validate

data at runtime first off let me just

mention that technically you can do it

manually so in this case yes we can

iterate over data check if the specific

property exists as well as has the

proper type and even though it sounds

super cute in reality it can get messy

pretty fast so instead if you ever need

to validate data in such a way Zod

library is a very valid Choice simply

because it provides bunch of options out

of the box and it's far better battle

tested than our own validation code now

you can use Zod in other scenarios as

well for example in my nextjs course we

use Zod to validate form submissions on

the client as well as server actions on

the server if you interested in learning

more about Zod just visit Zod Dev or you

can follow the link I left in the read

me first thing we'll need to do is

install the library so I'm going to open

up the terminal now I'm going to open a

new window technically you don't have to

just make

sure if you stop the server to start it

up again otherwise stuff is not going to

work so in this window I simply want to

run npm install

and S so now we install this library and

as a side note in few videos we're going

to talk about declaration files so

there's another reason why I'm

installing this Library so we install

Library okay everything's beautiful I

can close this window there's really no

need then we want to import Z from Zod

and essentially it's a named import and

then we want to construct our schema so

let's set this one up and you know what

I can just type it scratch I guess so

let me go over here let me go with

import then Z from and I'm looking for

my Zod Library again if we have

successfully installed should be

somewhere over here notice I have

dependency and there I have the Zod one

so we import the e z and then we want to

construct our schema so this is very

similar to what we have over here this

is going to be shape of our data but

difference well we'll use Zod methods

and this is going to be checked at run

time so I'm going to come up with t

schema and as a side note eventually

we'll set this equal to a different

value but not for now so in here we want

to go with z and then the object is the

method we're looking for so I'm pretty

much saying that I'm constructing an

object and here yes we pretty much want

to provide the same properties and and

as a side note I think I can remove this

something here and this one here as well

for now we'll figure out what we're

going to do there in a second and yes we

want to set up the validation for the

same property so this is not going to

change however in this case Zod provides

bunch of methods now again I'm not going

to go through each and every method in

this case we simply want to check

whether this is going to be a string and

this is super easy I can go with ID and

then Z Dot and then string so this

method essentially is going to check is

it a string or not and if it's not a

string if it's not present then

basically it's going to yell so now

let's copy and paste and we simply want

to provide different values so we're

looking here for name then we want to

get the

info we also want to set up an

image over here so

image um lastly we also have the price

so all of them are strings but the comms

are missing over here that's why I have

the errors so let me set this one up and

then as far as the tour we can actually

infer the type so I'm not going to leave

this for your reference since you have

access to it in a read me but

essentially I can go with type door and

instead of hard coding Zar has this

method of infer and it is actually a

generic and we should be familiar with

this one so notice the syntax

effectively we just go over here with

these angle brackets and then inside of

the angle brackets as far as the type we

go type off and then tour schema so now

we infer this T type and notice pretty

much the result is the same but now

we're nicely getting this from Tor

schema and like I said you have more

options for

example ID has to be a string but I can

also add min max and all kinds of

methods again this is just scratching

the surface and notice how we don't need

to change anything here in return we're

also here in a data but we do want to

right now add some checks at runtime and

in order to do that I'm going to rename

this to Raw data so this this is not

something we're going to be

passing and instead we want to go with

const result is equal to then we go with

our schema it has an awesome method of

array which we can invoke we're not

going to pass anything in and we also

have this safe pars so essentially safe

pars is not going to trigger

automatically the catch block we'll do

it ourselves so we're going to go save

Parts with we pass in our raw data so

now we're going to check this at runtime

actually not only at build time and then

since we have a safe part since this is

not going to trigger immediate error we

want to check for the success property

in the result so if essentially we don't

have the success property over there

then we'll go throw new

error and let's again and come up with

some message let's go with invalid data

for example let's access the result Dot

and we're looking for the error so if

we're not able to parse then we'll throw

the error manually and now where we have

the return instead of data which we

don't have anymore we're going to go

with result. data so that's where our

data is going to be located and again if

we're successful this doesn't change

still getting back that array but

difference will actually check

everything at runtime so now let me

navigate to the browser I don't believe

I'm doing anything so you know what let

me just log the results just so you can

see what we're getting back let's go

with the result notice we're successful

so success is true so we bypass that

error one and then we get back the data

over here so now I can navigate to my

map one and again I have access to the

door so let's log something let's go

with door Dot and again let's access the

name so this works now here's the

biggest difference if I'm going to go

over here and let's say add a property

which I'm expecting but it's not there

will actually get the error so if I'm

going to go with something and set it

equal to whatever number it doesn't

really matter if I go over here notice

how immediately this is going to trigger

the error so success is equal to

false and now I have this error message

in the console and again the cool thing

is that we're checking this at runtime

not just at build time okay and I think

at this point we're ready to talk about

typescript declaration files and why

they're so important and let's start

with a small recap if I were to go to

tutorial

and you know what no let me create a

file first so I want to create types DS

on here I'll write away export and I'm

going to go with export type and

random and here let's just go with name

and string if I were to import this so

import I mean with the type keyword or

without everything is going to work

correct pick because typescript knows

everything about this type random so I

can start right away using it in our

project so far so good but can you

explain to me this how come I right away

have access to the document object so if

I type over here press dot have access

to all of the methods and all of the

properties and of course I'm not going

to double check that so I'm not going to

prove that it's definitely a document

object but trust me the same one and

again good luck trying to build

something without this document object

so how come we have access to it because

I can guarantee you that I didn't set it

up anywhere it's not like I went to the

types and then started constructing the

document type I mean that would be just

a work for I'm not sure half a year so

what's happening over here well you see

when we work with typescript there's

something called declaration files and

the same is going to work for libraries

something we're going to cover in a

second but when it comes to typescript

they get included and then

essentially as we're working with

typescript it already knows everything

about the document so if we go here to a

type definition there is a definition

for this document like I said it's going

to be

giant but good luck

working without the document so in

here there's an info about every

property every method what it's doing

what um parameters the function is

expecting and that sort of thing so in

here technically there is no

functionality that's going to be running

in this file but there's going to be

type

definitions since when we work with

typescript typescript needs to know

everything about the shape of our data

otherwise as you saw with the straight

up JavaScript file it's just going to

complain so I guess first I'll show you

where

the Declaration files are located and

then I'll show you how we can add them

or remove them from the project now as a

side note since we're using the

boilerplate V

application it's already done for us but

yes if you're starting everything from

scratch you can add those things

manually ually Stars if we navigate to a

node modules and typescript which is a

package we're using under the lib notice

this long list well these are

declaration files again once you

navigate over here let me just find

something uh maybe this one over here

right notice you have these type

definitions it's not like in here you

have some kind of function that's

running no but you have clear

description of type definitions so so

again if you want to start using

something from the

Dom you can only do it if there's a type

definition for that something in one of

the files again you'll see in a second

if let's say we don't have access to

these files typescript is not going to

know what is a document or any other web

apis and the way we control that let me

just close the node modules again it's

already set up for us but you can do it

over here in this lib notice this Dum

essentially in the lib you specify the

set of bundle Library declaration files

that

describe the target runtime environment

and notice over here this D well if we

remove it notice something interesting

immediately typescript is going to

complain immediately typescript is going

to say Hey listen what document I don't

know what you're talking about

so essentially we can either set it up

ourselves or we need to have those type

definitions without those type

definitions we won't be able to

essentially successfully build our

project so let me just close this one

and navigate back to TS config let me

add the Dom since I do want to use it

since we're building for the web and

this leads me to the second Point yes

the same works with any Library you want

to use in our project remember how in

previous

video we were able to import Zod from

the Zod library and we were good to go

so notice how again typescript is not

complaining and in fact typescript knows

everything that there is to know about

the import it knows the types it

contains it knows the methods properties

and all that how well let's check it out

again we're navigating to node modules I

want to close this one we are looking

for a Zod in this case and under the lib

guess what again we have the type

declaration files and in there we have

type definition and therefore once we

start using the

library typescript has no issues it

right away knows what the method is

expecting what is the interface and all

that that which leads me to another

Point yes if you're going to install

Library which doesn't have the

Declaration files basically there are no

type definitions you won't be able to

use it now the good news that there is a

repo which essentially

contains the types for a bunch of

libraries but first let me show you what

happens if we install such Library uh

what is the result and again this is

just random example I'm going to use

bcrypt j s which is a password hashing

library and technically this is optional

I mean you don't have to follow along I

just want to showcase something so let

me go to a separate terminal window let

me install it okay I installed the

package clearly see that it's in my

dependencies okay good let me remove all

of this I'm going to go with import

bcrypt Js from and definitely have the

library but check it out so essentially

typescript is complaining there is no

declaration file so same issue like we

had with the straightup Javascript file

and like I mentioned before the solution

is following there is a repo which

contains bunch of types and I left the

link in read me so let me try to

navigate over here and in this repo

under the types you'll be able to most

likely find the library you just

installed because it contains like What

7,802 entries so essentially you have

typescript types for all of these

libraries and the one that we're looking

for in this case is bcrypt JS otherwise

we cannot use it in a project and the

way we install the types is following so

we go with npm install we're going to go

with save dev then at type

and then bcrypt JS so our specific

Library let me grab this line of

code and the moment we do that

typescript is going to know everything

that there is to know about this bpjs so

if I'm going to go over here type dot

notice I have access to all of the

methods the import provides hopefully

it's clear why typescript declaration

files are so important when we're

building the typescript project and with

this in place we can move on to the next

topic okay and up next let's cover

typescript config file where as the name

already suggests we can configure our

typescript setup now if I'm being

totally honest I actually find this

topic super boring and therefore I'm

planning to cover only the properties

which in my opinion are the most

important ones but if you are interested

in specific property or maybe you feel

like a rebel and you want to explore all

of them feel free to utilize this link

in the read me so this is the link that

you're looking for as you can see it

guides us back to

documentation and you can start

scrolling and you'll see that this is a

giant file where pretty much you can

find everything that there is to know

about the DS config again big picture

this is where we control our typescript

configuration I just want to mention

that we have this include and in here we

point to where the typescript files are

going to be located so in our case where

it is well it's in the source this is

where we're setting up our project then

we have compiler options and let's start

with the target one over here and with

this one essentially we control the

output code so navigate to a typescript

playground notice I have this export con

and then the arrow function now if my

target is a JavaScript language version

which has the arrow function already

then as you can see the output code is

going to be pretty much the same but if

let's say I change this to

ES3 notice how it didn't have the arrow

function therefore we get good old

regular function so this is what we

control over here in the Target now as

far as the module

remember with this one we're controlling

what kind of module syntax again we're

going to get back in the output code in

the lib this is where we were

controlling the Declaration files that

we're getting and pretty much after that

the one that we're interested is the

strict one so this is this flag which

controls how bunch of the errors and the

warnings are treated so if we're going

to go with false then bunch of the

things that technically should fail are

not going to and we'll be able to build

the project now if we set this one to

true then we have the strict type

checking set to true and then for

example we have this no unused locals so

if I were to go to tutorial and come up

with let something is equal to something

notice how I get this warning that

something is declared but I'm not using

it well if we go here and set it equal

to pulse or just remove it then

essentially we'll have no warning

message anymore again just a example of

one of the properties that we can use

this concludes the TS config and with

this in place we can move on to the next

topic and up next let's quickly cover

class syntax in typescript now if you

don't use classes in your project feel

free to skip this section Al together

since most likely you'll see very little

benefit and first let's start with a

recap that classes in JavaScript serve

as blueprints for creating object and

they also have this special method

called

Constructor which is automatically

called when we create a new class

instance with the new keyword

and this keyword inside of the

Constructor refers to the object being

created so in this case I have a class

notice we need to use the keyword class

then the name is book now the convention

is to go with uppercase but technically

you don't have to and it has a

Constructor it's a typical method

basically we can pass here pams and in

this case I have title and the author so

every time I'm going to go new book and

pass in the values they will be set

inside of this object inside of this

class instance and in order to set those

properties I need to go with this dot

then the name of the property in this

case title and I just set it equal to a

value just being passed in so in this

case it's deep work and then the author

name now since we're working typescript

notice how we have few red Squigly lines

how do we fix them for STS we we need to

set up the annotations over here in the

Constructor so what is going to be the

type of the title and author and here

let's just go with string and string and

of course we can use the Boolean we can

use the number pretty much everything

that we have learned up to this point

but here's the kicker I still have the

red squigglies inside of the Constructor

and you would think okay we can go over

here and say that this is going to be a

string and number or Boolean but when it

comes to classes and typescript we

actually need to go inside of the class

and explicitly set the type for the

properties we are setting inside of the

Constructor so in this case since I have

two of them I have title and author yes

I need to go above my Constructor and

essentially set this one equal to a

string and the same is going to go for

author so I set both of them up and then

notice now I don't have the red

squigglies

and I'm able to create those instances

again result is going to be exactly the

same I will still have my instance in

this case de work with the title and

author properties the difference now

typescript is happy as well so I'll be

able to build my project just like a

normal JavaScript we can also set

instance properties or they're also

referred to as default properties and

essentially the idea is that we set this

property inside of the class instead of

the Constructor and then they get

automatically added to all the instances

we create now how's that going to look

like well imagine we have this checked

out property and it's a bullan and

initially it's always going to be false

so yes definitely we can go here with

this Dot

checked out and again notice we're not

passing anything in a Constructor it's

going to be set by default and I'm going

to go with false so now I can navigate

over here and say checked out and set it

equal

to Boolean correct so this is going to

work but since I'm not passing this as a

parameter we might as well set this one

up as a default property so I can just

move this line of code and where I have

the checked

out yes I can still keep it as Boolean

and set it equal to false but we can

also rely on the fact that typescript is

going to infer this value so this is up

to you you can go like this or you can

set up the checked

out like

so equal to false for example or true

and then typescript will immediately

infer type now again just like other

times when typescript infers the type

just be mindful of potential pitfalls

you might face and if let's say we're

going to go with deep work and checked

out we should see the value in the

console so at the moment it's false and

let's say if we decide to set it equal

to true that's also an option so let's

go with deep work checked out and let's

set it equal to true now since it's a

Boolean we can definitely do so now it's

equal to true but if I'm going to change

it to hello world of course this is not

going to work typescript is going to

complain because it is a bullion so this

is how we can set up default properties

in classes in typescript when we work

with classes in typescript we also have

this read only

modifier which does exactly what the

name suggest

essentially if we add this read only

modifier to any of the properties we

won't be able to modify them for example

if I'm going to go to my title add read

only yes I can still read the value for

example I can go with deep work and

title and for some reason I keep

forgetting to set up my

logs so we can still nicely access the

value problem is going to be if we try

to change it so if we go here with deep

work. title and set it equal to

something else so this is not going to

fly because now we have this read only

modifier added to the title property

also in typescript we have private and

public

modifiers which control whether we can

access the property or the method from

the outside now as a side note by

default everything is public therefore

if we go with deep work and type do

notice we have access to author checked

out and title but if I'm going to

navigate over here and let's say

set checked out to private notice how

still will go deep work and now I only

have access to author and title so yes

of course I can go over here and say

public just keep in mind that's the

default Behavior let me just set it up

so I'm going to go with with public over

here and also as a side not you can

combine them so notice in this case I

have already read only four the title

but I can also say that this is going to

be a public one now typically the way we

control some private property is by

setting up some kind of method which we

can call from the outside just to

Showcase that let me go with the

method and I'm going to call this check

out

then let's set up the functionality

where I'm going to go with this dot

checked out and I'm going to set it

equal to true so as you can see I'm

still able to access the property from

within the class but like we just saw we

were not able to see the checked out

value from outside so in this case I can

go with deep work then let me call the

method check out out and now if we'll

take a look at the Deep work again in a

console the checked out should be set

equal to True correct so let's navigate

back over here and notice of course the

value right now is true so this is

typically how we would access the value

we set this equal to private so we

cannot access it from the outside but

then we set up a method which actually

controls this value and just to hammer

home that we can mix and match I'll set

up few more methods one is going to be

is checked out where we're just going to

check the value and then I'm going to

set up the private method so again this

is a bit of Overkill but I'm just going

to add this public one over here as you

can see that's the default Behavior

everything is public then we're going to

go with another one where we're just

going

to check what is the value so we don't

need to take a look at the console so in

here I simply want to return this Dot

and checked

out and then also I want to set up the

private one where we're going to toggle

so this will be a private method toggle

and let's come up with the name status

that sounds like a good one hopefully I

have no spelling errors and from this

function I simply want to return the

opposite value so I'm going to go with

this Dot and we're looking for checked

out now since this is a private one

again I'm not going to be able to call

it here where I have my instance instead

where I have the checkout one I'll just

set it equal to this dot so now I'm

accessing the private method and I'm

invoking the toggle checked out status

like so and now let's just navigate over

here I guess let's clean up our code a

little bit and and let's just invoke few

functions so for STS let me go with deep

work we have checkout that's the one

that we want to invoke and after that

we're going to go with log and again

we're looking for our instance and now

we want to check the actual status and

notice over here this is set equal to

true so by default it was set to false

then I ran the checkout method which

essentially just toggles the value and

then I logged in a console that it's

equal to true now let me try this one

out let me run it two times and now this

should be set equal to false because

we're just toggling back and forth so

this is how we can use public private

and read only

modifiers in classes when we work with

typescript and up next let's see an

awesome shortcut we can use which is

going to say was quite a few lines of

code now for starters I do want to clean

this up since I want to discuss Getters

and

Setters in the upcoming videos and I

think it's going to be too much logic

inside of one class and also let me

remove the first two properties as well

as all of this code over here in the

Constructor so the shortcut is following

at the moment notice if I go with my

deep work and type dot I don't see

anything correct since we didn't set the

properties correctly but what we can

also do is add readon public or private

modifier in front of the parameters and

if we do that it will be automatically

set as a property with the value inside

of the instance so let me show you what

I'm talking about we go here with read

only and yes even though

it might seem redundant since by default

technically this is public if we go here

and set up the public this will be set

in my instance now we're not going to

use this value but just to Showcase that

same is going to work with private I'm

simply going to go over here and say

some value and let me set it equal to a

number so now if I go to my deep work

right now and type that notice I

immediately have access to author and

the title so this is the shortcut we

don't need to use this anymore over here

we don't need to explicitly set these

properties in a class we simply can use

either read only or public or private

and effectively immediately tcri behind

the scenes is going to set those

properties with the appropriate values

when we create the instance now since

you might not believe me about the Su

value let's come up with some random

function let's just explicitly say that

this is going to be public and I'm going

to call this get some value okay and

then we'll return this Dot and some

value so notice inside of the class I do

have access to it so let me call get

some value and we do want to place it in

a con log I guess so get some value

let's invoke this let's set up our log

let's move this inside and the moment it

says

undefined because I did not provide the

value okay so notice of course it's

missing so I have some value and since

I'm looking for a number I'm going to go

with

45 so once we log right now everything

is correct so again this is an awesome

shortcut we can use

in the Constructor we can add one of the

modifiers and this will automatically

set those properties in our instance and

up next let's work on the example with

Getters and Setters which are special

methods that are access like properties

more specifically let's take a look how

we can combine them with the private and

public

modifiers which we covered in the

previous video

so one cool thing that we can do with

the getter is to set up a computed

property so essentially I can create the

property on a fly now in order to create

the getter or the setter we want to go

with get or set eord then we want to

come up with a name so this essentially

will be a property on this deep work and

in here I just want to compute some

value so in this case case I'm going to

go with the template string first I'll

access the title and I'll combine it

with the author this dot author let's

save it and now we want to go with our

deep work and notice we have essentially

this info property now since we're

returning the value I keep forgetting

that we want to place this inside of the

log and in console now we have title

followed by the author again what's

super cool is that we can create this on

a fly so I can just come up with the

property then do my computation and I

didn't need to set anything in the

Constructor or above the Constructor and

the same way we can set up the

setter the keyword we're looking for is

set and in this case again I'm going to

control that checked out property first

let me start with a set name now just

like

good old

method we can provide over here

parameters and in this case I'm going to

call my parameter checked out now we do

need to provide a type and then inside

of the setter we're going to go with

checked out and we'll set it equal to

our parameter value and then let's

navigate to the console log and right

after that let's invoke our Setter so

we're going to go with our instance then

and set our name and in this case again

this is the property so we set the value

now if I'll try to go with hello and

notice how typescript immediately

complains so let me go back and yep I

want to go true and now I don't see

anything in a console since I'm not

logging let me try one more time where

I'm going to go deep work and if

everything's correct the checked out

should be equal to true and we can use

the private and public as you can see

again by default everything is already

public but let me just showcase if we go

here with private now we can only invoke

this inside of the class so this is not

going to work let me comment this one

out and let me set up two more

Getters one is going to be for the

checked out value and in the second one

will actually we use the check out

method a lot of checkouts so let's go

over here with get now as you can see

the name can be exactly the same because

one is a Setter and other one is a

getter by default it's going to be

public and then from this one we want to

return checked

out and now Just for kicks let's set up

a getter but inside of it let's invoke

the setter just to make it more

confusing so let's go here with public

even though again technically it doesn't

change anything in this case I'm going

to go with some info we're not going to

pass anything in and in order to access

our Setter our private one we want to go

with this. checkout set it equal to true

and then after that we want to return

and since I want to return the same

value you know what let me copy from the

info and and let me just

overwrite in here so now let's navigate

to a console first we want to go with

log I guess we're going to go with deep

work then some info so this is going to

set our checkout equal to true and also

return this value and also

let's copy and paste and set up one more

and in this case I'm looking for my

getter the checkout one and once I

navigate to a console as you can see at

this point it's false then I get back

the

same info the title followed by the

author and at the very end we can see

the checked out value which is now equal

to true and that's how we can use

Getters and Setters with public and

private modifiers and up next let me

showcase how we can implement the

interface by the class and if you

remember the video types versus

interfaces it was one of the things

which we could do with the interface but

we cannot do with the type so let's

imagine we have the interface and the

name is I person which essentially

stands for interface person because

there will be a class of person let's

come up with some random properties so

we're looking for string then also we

want to set up the age number and you

know what let's go with greet method and

it's not going to return anything and

it's also not going to take any

parameters then we're going to go with

class let's come up with the name in my

case person and we go with this

Implement which essentially is promising

that it will provide all of the

properties and methods defined in in the

interface so in this case we're looking

for I person that's the interface I want

to use and in here let's go with the

shortcut which we covered before so I

can go with public now what is the name

it's a string correct so let's set up

and also we want to go here with public

age now this will be a number we're not

going to set up anything in the

Constructor well we don't have to we

still have a red squiggly line because

there is no method so right after

Constructor let's go with greet it's our

function and let's just log some stuff

over here in this case I'm will go with

hello my

name is Slim

Shady and this is name and also I

am this. age let me access this. Ag and

we're going to go with

years old now we do want to set up our

instance so let's go with

con and hipster we're looking for a new

person let's provide a name Shake and

Bake and as far as the years well let's

go with 100 and then at the very end

let's invoke

hipster GRE and if everything is correct

we should see the text in the com so so

that's how we

can implement the interface with the

class again something we canot do with

the good old type Alias okay and once

we're done with tutorial let's put our

typescript knowledge to a good use and

create a small tasks application as far

as the setup for this project I'm going

to set my code editor and browser side

by side but you you don't have to it's

just my preference since that way I

don't have to switch screens like

gazillion times also I will set up a new

page in my case I'm going to call this

tasks

HTML keep in mind technically you can

build everything in index HTML I just

think that it's going to be easier if we

separate the tutorial from the project

so here's what we want to do navigate to

the route again please don't set this

one up in the source we want to create a

new file and I'm going to call this

tasks HTML now I will create a basic

HTML structure and in the vs code

essentially we just do that by getting

the exclamation point I believe I mean I

haven't created the straight up HTML

project in so long that I already forgot

so yeah basically we want to click shift

and back tick and notice we get the this

suggestion from EMT that you can create

a HTML structure now in my case I'm

going to call this tasks app or tasks

then also there's going to be a link for

CSS so that is coming up and in here for

now let's just say tasks app let's save

it now this is totally up to you you can

navigate in the browser and just stay

there or we can actually go to to main

DS and notice we have both of these

logos well at the moment these links

navigate somewhere externally basically

back to typescript and vat and we can

actually change this around where I'm

going to go with forward slash

and

tasks and of course if you named your

page differently please make sure that

the H matches and I'll do the same for

this one so now once I click on one of

them I'm going to navigate to the tasks

app now I'm not going to set up the link

back I don't think there's any need for

it for now I think we can close the main

one but we will return to it and also

let's create an Source tasks DS so this

is going to be our typescript file where

we'll set up the logic let's go with Ds

now in this case we're not going to

import that in the main DS we actually

want to go there directly to

tasks somewhere here the bottom of the

body we want to go with

script then we're going to add type

module and now let's look for

Source we're looking

for tasks I believe yep that was the

file and I always prefer to set up some

log just so I don't run around like a

headless chicken looking for a bug but

maybe there's an UT wrong or something

along those lines now for some reason

yep everything is fine so I see over

here the tasks so I know

that my logic works then let's navigate

uh back to tasks

HTML and now above the script

effectively we want to set up the

structure for the application so I just

want to add some HTML elements now this

is totally up to you but I also provided

some CSS just so it looks a bit more

presentable now you have two options you

can either get it from the final folder

so navigate to the final

repo look for typescript tutorial and

then more specifically look for task CSS

so I didn't want to add this code in the

main CSS file so we're going to create a

separate file for that task CSS and then

just grab that code or you can nicely

navigate to the end of the readme and

just copy this code again there's a

bunch of Base Styles so let's not worry

about the CSS too much as far as the

actual CSS for the project there's not

that much code but I'm not going to go

over it because this is definitely not a

CSS course so just select everything

inside of the back dick where you see

the CSS

then we want

to go I guess let's set up in a source

doesn't really matter we're going to go

tasks CSS copy and paste and now where

we have a tasks HTML we want to set up a

link we're looking for the CSS one and

basically it's in the same or it's not

sorry it's not in the same folder we're

actually looking for t

CSS so once we add that I mean at the

moment most likely we won't see anything

but once we add our elements we should

have a nice CSS as well and with this in

place now let's set up the structure and

I'm not sure whether I mentioned that

technically the CSS part is optional so

I mean it's not going to affect any of

our logic our application is just going

to look tiny bit more representable then

we want to go with tasks of some kind of

value as a sign note we might need to

refresh yep now everything works now I

can see my tasks over here then let's

create a form now we won't have the

action but I do want to add the class

and even if you're not using my CSS

please make sure that you use the same

classes or if you use a different class

make sure that you remember that when we

are setting up the

logic then let's go with input inside of

it the type is going to be text then we

want to go with another class and we're

going to go with form input save this

okay this is what we should see then

also let's add a

button type will be equal to submit okay

beautiful let's add a class name

BTN let's call this add task okay again

I'll have to refresh and then right

after the form we have anord list class

let's go with list we're not going to

place any items so we will place the

items dynamically with the help of

JavaScript and then at the very end

let's just add a test button because

there's something we need to discuss

first so technically this is not going

to be part of the project but it's super

important we cover two things and

therefore we're going to go here with

the

button so we're creating the good old

button let's add a class of test BTN and

let's just right click me let me save

Let me refresh and this is what we

should see in the browser and if you

have the same result now we can move on

to the next step okay and before we

start typing away let's address these

two important points first when we use

Query selector we actually get back the

element which is the most General Base

Class that only has the methods and

properties common to all kinds of

elements so that's Point number one

second there's also potential for null

and we also need to address that and no

we cannot build this project unless we

cover both of these things extensively

now once we do it should be a smooth

sailing so first let me just showcase

the two important points

if we go with cons button we know we

have access to a document correct

because we have the Declaration files

and document has this awesome method

called query selector where we just pass

the class in this case and we can select

the element and everything is awesome

but as I hover over the button notice it

can either be an element so it's going

to be an issue if I try to

get some properties and methods that are

only specific to buttons which is

actually going to be our second point

and also it can potentially be null now

why do we care about that well let's say

if I want to go with BTN and then Dot

and event listener it's not going to

work well technically it's going to work

because typescript is going to fix my

code but notice it's only going to work

if we go here with this question Mark so

this is one approach how we can fix this

because as far as typescript is

concerned there's no way to tell whether

yes for sure we're getting back to

button unfortunately again this is built

time this is not

runtime so typescript is like okay

you're selecting the element from the

dumb potentially well this can be wrong

correct and in that case you're not

getting back the element you're actually

getting back null and we need to handle

that also don't be surprised if in few

cases and I sign not yes we'll cover

that

actually when we talk about the element

point you might need to do more checking

you might need to do something like this

where you go with if button and only

then run the code so this is one

approach how we can handle the case

where element is null and yes every time

you'll want to do something with the

element you'll essentially need to first

check whether the element actually

exists now another approach to deal with

the null issue is by setting up the non

null

assertion operator so effectively in

here I'm telling T script yo I know for

sure that the element exists over here

and in that case notice I can go here

with BTN then Dot and then add event

listener and I don't need to use anymore

the optional chaining and the same is

going to work if I'll try to run for

example disabled on a button I won't

have to check

for the element whether it's actually

present so in here I'm just telling T

script listen I know a bit more about my

project than you do and I know for sure

that the element is there and actually

if we take a look at the main TS I

believe it was over here now don't worry

about the code after essentially they're

just dynamically inserting the elements

and all that notice this one over here

where they go with document query

selector they grab the development

they're looking for the ID over here and

then they just tell typescript Hey

listen we know that the element is going

to be there now how do they know that

well we take a look at the index

HTML notice this ID it's app correct so

you have two

approaches you'll see both of them used

extensively as far as your project it

really depends if you like this approach

where essentially you let typescript

know just be mindful if the element is

not going to be there then of course you

will have runtime errors or or you can

use the optional chaining and then here

and there you might need to actually

check whether the element is present so

that's the first point that I wanted to

address now the second one is following

I use over here this nonn assertion

operator okay everything is awesome but

what if I want to run disabled method I

know that the button has this particular

method so let's say I go here with BTN

Dot and then I'm trying to type but I

can see that it's not present so

something is off why I have such issue

well remember we are getting back what

we're getting back actually an element

which is the most General base class

from which all

elements in a document inherit now this

one the element has only the methods and

properties common to all the elements so

where I'm going with this well there's

going to be instances where you select

elements and you need a specific method

or a property which is only on that

element and this is the case the button

I know it has disabled one and I know

for sure that I definitely want to use

it but I'm not able to because I'm

actually getting back the element now

let's take a look why is that a case

let's go here to type Ty definition and

notice the query

selector so query selector surprise

surprise is what a

generic now it's looking for the type

and notice how there is actually type

constraint where it says yeah you can

pass in the element but it needs to

extend from the element so this is a

more interesting case for type

constraint instead of our string and

number our still EX examples actually

this limits the element to the element

and not only that notice how it actually

provides this one as a default and what

does that return it actually Returns the

element we passing over here or it

returns null so all of the things we

learn we can now nicely use when we

inspect the documentation so now it's

very easy for us to look at this

documentation and be like okay so we do

need to provide the element we want to

select it needs to extend from the

element and if we're successful we're

actually going to H it back so now let's

navigate back and in a query selector we

want to set up the angle brackets and

then we want to look for

HTML button and element so that's the

one that we want to pass in so now we're

not getting back the element or null

we're actually getting back our HTML

button element so now if we start typing

notice BTN disabled and we can nicely

set it equal to true now before I show

you the type assertion option which is

another approach you'll see let me just

remove this non null assertion operator

and showcase that here and there you'll

have to actually check for the button so

remember our second option where every

time we will use a method for example ad

event listener we need to add the

optional training which as a side note

is already done by typescript in this

case in this case in the case of

disabled it's going to be a little bit

different so if we'll try to do that

typescript is actually going to complain

it's going to say hey L and you canot do

that so instead we'll have to check

button and then we can set it equal to

True again this just brings me back to

the point that we have two options over

here and we can also always add this

exclamation point and as far as the

second option if we don't want to pass

here in the generic we can also use the

type assertion so let me just go here

with disabled and let's set it equal to

True again

and let me remove now once I do that

typescript is going to complain and

another approach that you'll see is this

one where we select yes we're getting

back the element but then we use that

type assertion and we say yeah actually

this is going to be HTML and then button

element now I personally prefer the

other approach and that's why throughout

the course you'll see that one but

definitely don't be surprised if you see

something like this in the code base

this is also an option we can take where

we select the element and then we just

use the type assertion and you have the

example in the read me so I guess I can

just remove pretty much everything over

here because we'll start everything from

the scratch and we'll start working with

our form so you know what let me clean

this up we also don't need that silly

button over here since we covered two

important points and now we're ready to

move on to the next step okay so let's

start working on our project and in this

video I want to select three elements I

want to select the form I want to select

the form input as well as the list so

form input is where we'll get the value

We'll add the event listener on the form

so every time we submit the form we will

grab the input value and also we want to

get the list since every time we'll

provide here a task if the value is

there then we'll basically add it to our

list and also this is where typescript

is going to come into play we'll need to

set up our type so this is something

interesting every time you work on a

typescript project yeah pretty much one

of the first things you'll want to do is

to start at least setting up the shape

of your data this is at Le at least in

my opinion biggest differences between

the regular project and a typescript one

you'll always always have the types or

interfaces somewhere because typescript

needs to know about the shape of your

data so let's start I guess

by selecting all three of them I'm going

to go with task form now I'm not going

to use the nonnull assertion

operator throughout the project I'm just

going to use that optional chaining so

we're going to go here with do docent

then query selector I do want to set up

the angle brackets and I'm just going to

say that this will be a HTML form

element or

no then let's go with the class and

we're looking for the form and I believe

I forgot to mention you see there's no

way for typescript to know that this

definitely is a form that's why we need

to provide over here this form element

so it cannot magically go to the HTML

and figure out that since we're using

the form class then for sure we're

selecting the element which is actually

a form that's why we get back this

generic element and that's why we need

to use the generic to provide what is

the element we're actually selecting

hopefully that is clear const form input

is going to be the next one we're going

to go with document query

selector then will provide the

HTML input element so this is the

element I'm looking for input element

okay good and then the class is Dot and

then

form input

now I think I can make this one so

everything is in one line I'm pretty

sure we can see everything that's

happening I mean you know what no let me

make it like this and then

Also let's go with const task list

element and this one will be equal to

document then query

selector let me add the angle brackets

as far as the class we're looking for

list and over here we want

HTML ul and list element and my

apologies I'm just going to be kind of

randomly moving the this stuff over here

don't worry we shouldn't have issues

with the later code it's just these

select lines then let's create the type

and effectively we will have a task with

description which is going to be a

string and is completed which is going

to be a bullan so let's set up this one

type

task then let's go with the description

set it equal to to a string and yes as a

sign not you can set this one up as

interface as

well it's just my preference to go with

typ aliases and we're going to go with

Boolean and

then I'm going to set up an array of

tasks so this is where we'll store the

tasks and as a sign note eventually

we'll grab these tasks from the local

storage as well so think of this as the

state for our applications so we're just

going to go with tasks it's actually

going to be equal to an array of

tasks and for now it's just going to be

empty array okay and now let's start

setting up the functionality so we want

to add event listener on a form we're

going to be listening for submit events

we do want to prevent the default so we

want to handle everything with

JavaScript and after that inside of the

Callback function we want to grab the

form input value if some value is

provided will actually wipe everything

clean and return and of course before

that we'll have to do quite a bit of

logic and if there is no value then

we'll just set up the alert so let's set

everything up we're looking for task

form again we can rely on typescript or

we can manually add this optional

chaining operator ourselves then we're

looking for ad event listener like I

said we're looking for submit and again

notice how helpful typescript is so

right away provides all the possible

events that we can use over here for now

we will provide call back directly but

in the following video I'll show you the

Goa we need to be aware of remember we

have access to the event now if we hover

over we can see the that actually it has

a type of submit event something

important we need to keep in mind and

then let's go with event we're looking

for prevent default and we just invoke

it so now we'll handle everything with

JavaScript after that let's grab the

form input and more specifically we're

looking for the value property which

again is on the form input I'm going to

give it a name of task description let's

set it equal to form input

same deal we don't have this non null

assertion operator so again we can just

rely I guess on typescript or in this

case it simply complains so we'll just

need to add this optional chaining so

now we're grabbing the form input value

if we have something in there if the

user has provided something then we'll

do a list of things if not then go with

alert and

we'll just say please enter a task

description again it's not going to be

the most complex application ever let me

refresh and notice if I don't provide

anything essentially I just get this

alert box now if we are successful again

there's going to be a list of things

that we will

do but once we're done adding a task to

the list once we're done rendering the

tasks and updating the local

storage at the very end regardless we

want to set the form input value back to

an empty string and we want to return

since I only want to hit this alert if

no value has been provided now also for

time being you know what let's just log

here let's just say task description so

if I provide some random value check it

out I have it here in the console if not

again we have this alert box and what

this in place now we can move on to the

next task okay and before we set up the

logic to add new task to our list let me

showcase the event object gotcha and as

I know this is something you'll also see

in react section of the course so pretty

much the main idea is going to be

exactly the same and it is following you

see if we provide over here call back

function directly everything's awesome

typescript knows that yeah it's actually

a submit event but it's not going to be

the case if we set up the reference so

can go here with function create task as

a say not I don't think I'm going to

keep it so I'll just set it up and

eventually remove it but this is totally

up to you of course you can also keep

this code if we're going to go over here

and basically take all of this

logic like so everything should work

correct we have access to the event and

now we can just replace it well let's

see let's go with create task and check

it out so typescript essentially saying

that event right

now has the type of any so this is the

case where if we're setting up

functions and providing them as

references here when we're listening for

events then yes we'll explicitly need to

provide what is the type so in this case

we're looking for submit event and once

we do that again our logic is going to

work I can provide some value over here

and everything is awesome and the same

is going to work with the empty value

and yes the same you'll have to do in

react now in there the code is going to

be more complex but the idea is the same

if you're listening for some kind of

event and you set up the logic directly

in a callback function yes event will

have that correct type straight out of

the box but if you're setting up a

function which you're then using as a

reference it's not going to be the case

something important to remember okay and

up next let's see how we can add task to

our list now in this video we're not

going to set up the logic to render any

tasks on the screen that is coming up so

most likely we'll do right after we are

able to add task to our list and in here

I want to First create function I'm

going to call this add task and as far

as the parameter it's going to be a task

but this is where we set up the type so

we definitely say that we need to

provide the task and we're not going to

return anything from this function and

as far as logic we want to go with task

I'm sorry tasks and then push and we

want to add our task so whatever we

provide over here then we want to

navigate back to our if block and you

know what let's add three comments we'll

say add task to list then second one

will be render tasks and then we also

want to update the local storage so all

of that is coming up for now inside of

the if block I want to construct a task

so if I have a text I want to go cons

task is equal again to my type my task

type and I want to set it equal to

description this will be equal to task

description so this will be my string

and then as far as the completed one we

will hard code so go with is completed

and we'll always always set it equal to

false so once we create task now we can

invoke add task and pass in a task and

since I have the correct type everything

is good script is not complaining and we

can actually log the tasks here so let's

go here with tasks let's add something

so let's say first task and check it out

now I have my array with my first task

if I go with second task it's not going

to be surprised if we have two items in

the array and with this in place now we

can move on to the next step okay and up

next let's render the task on the screen

now we will call actually render task in

two places so for now we'll only call it

here in a task description block so if

we're successful we'll just render it on

a screen but also once we're able to

grab the tasks from the Lo local

storage will iterate over and render all

the tasks on the screen so think of it

this way not only we want to render the

task once we add new one to the list but

also when the user first navigates to

the page or we refresh we want to grab

the tasks from the local storage where

they are nicely saved and we want to

render them on the screen as far as the

function first we just set up our

keyword I'm going to call this render

task and again it's looking for a

parameter but parameter has a specific

type and it's equal to task then inside

of the function first I want to create

the element and in order to do that I

need to come up with the name in my case

I'm going to call this task element then

we go with our document it has a method

of

create

element and we just need to provide what

element we want to create so either we

scroll down or we just type Li and now

we successfully create the list element

then we also want to add the text

content basically it's going to be the

value for our task description the

property is text content and we set it

equal to task so whatever it's passed in

and

description and then at the very end

remember we have our list somewhere here

that's the one if

it exists if it's not null then we want

to add this element to the list so we go

with task list element up in child again

typescript Auto formats for us and just

add this optional chaining and then we

pass in our task element so now let's

navigate up where we have render tasks

and we want to go here with this

function pass in a task and now let's

try it out if we're successful

we should see the task on a screen so

let's again go with first task and check

it out we successfully created the

element on the Fly same is going to be

with second task and all the tasks we

add to the list all right and I think we

are at the point where we can add local

storage to our project because it's nice

that we can render all the tasks we add

to our array however if we na away or

just refresh notice how essentially we

lose all the tasks since they're just

saved in the memory now before we do

anything I actually want to make sure I

have nothing in a local storage

otherwise I mean I might get some weird

bugs so let me navigate to my local

storage and just clean everything again

Let me refresh I have nothing in there

so now again I can make this one

smaller and as I said I'm looking for

the console okay good

and now as far as the functionality we

want to create a function called update

storage and in there we will use the

local storage more specifically set item

method and we'll need to provide the

value and just stringify our current

tasks so in my case I'm going to do it

over here so we go with function let's

call this update storage and as a yes

we'll call it in multiple places so

update storage

as far as the parameters well we're not

going to pass anything in and as far as

the functionality we're just going to go

with local storage then let's go with

set item as far as mining it's going to

be tasks then comma and then we're going

to stringify the tasks as a sign note

yes pretty much every time we will add

the task to our list

or when we click on the checkbox and we

edit the task when we set it equal to

completed or we uncheck that yes

effectively we will overwrite all of the

values that we have in the local storage

with this new one so grab the tasks and

overwrite with the current

values now when do we want to call it

well for starters we want to do it over

here so we're going to go with update

storage let's invoke that and you know

what I will actually open up

a bigger window I think it's going to be

easier to see so that's my

tasks let me open

up application okay good and then let's

go with first task again Yep this is

what we have over here notice tasks and

I have a d and if I'm going to go with

second task now this is going to get

added to the array so this should cover

when we add the task to the array so

this should cover the form submission

now we also want to handle when we load

the page so at the moment we always set

it equal to an empty array but we want

to change that and order to do that we

will come up with a function called load

tasks now you can set it up with all of

the functions but I'm just going to do

it over here since in my opinion it's

going to be easier to see the entire

functionality we we are looking for a

return and from this function we want to

return an array of tasks so an array and

type is going to be the task now inside

of the

function first let's grab the tasks from

the local storage so we're going to set

it equal to stored tasks that is equal

to local or I'm sorry not load local

storage it has a method of get item and

we're looking for the tasks now here's

the kicker just like previously this can

be a null and we definitely need to

handle that so in here when we set up

the return we're not just going to go

with store tasks actually we will set up

optional training and we'll say hey if

there's a value okay awesome parse it so

we're going to go with store tasks

because keep in mind we cannot store

essentially objects in the local storage

we can only Only Store strings that's

why we went with Json string ify and now

we want to parse that value but we only

want to parse it if we get something

back correct if not well then we'll just

return empty array and now where we have

the tasks we'll actually go with load

tasks we will invoke it and since

potentially now we can get some tasks

from the local storage we also want to

iterate over and render the tasks so for

every task we have in the local storage

in our array we want to call render task

method so I mean somewhere after the

tasks we want to go with the name so

tasks then dot we're looking for for

each and we simply can pass in the

render task now let me showcase

that

essentially it's pretty much the

same as we have over here so notice we

can either go tasks and for each and

then pass in the call back function or

you simply provide the reference to

render tasks and now let me navigate to

the browser and if everything is correct

whatever tasks we have in local storage

once we refresh we'll see them in the

browser as well all right and at the end

of the project let's also add the

checkbox to our list item and every time

we click on checkbox we'll be able to

control this is completed so by default

it's false but then once we click on a

checkbox we can actually toggle that and

I think I'll try to cover the part eight

and part nine in this video hopefully

it's not going to be too long STS we

want to navigate to render task and at

the moment we're just adding the list

item to our list but we also want to add

a checkbox to the item and then add that

item to the list hopefully that makes

sense so let's go here with checkbox we

have const task checkbox that will be my

variable we're looking for document then

dot then we want to create the element

and this is going to be the input so not

list item we're looking for the input

and then we'll set the type to be equal

to a text box so we're looking for task

checkbox type

and we set it equal to checkbox then

let's set check equal to is completed

Again by default it's going to be false

so let's go with task checkbox we have

the checked property which controls that

and we want to set it equal to task and

then is completed and now before we add

task element to our list we also want to

go with task

element so task element then

upend child and we want to pass in task

checkbox and check it out now we have

the checkbox at the moment it's not

doing anything since we don't have any

functionality but we'll change that

right after we create the checkbox I

also want to add the event listener and

the event we're going to be listening

for is going to be change so before we

add it to a task element element let's

call

toggle

checkbox we're looking for our task

checkbox that's the element then add

event listener we're going to be

listening for change event we're not

going to access the event and as far as

the functionality we want to go with

task and then is completed set it to the

opposite since we're going to be

toggling and the way we do that is

following so we go with exclamation

point and task is completed so we set it

equal to the opposite and then we call

update storage so now once I click and

you know what let me showcase that on

big screen again let me start from the

scratch just so you don't think that I'm

cheating over here and if we take a look

at the tasks okay this is what we have

is completed is equal to false but then

once I click notice it's set equal to

true so when I refresh I get back the

same result this concludes the tasks

project hopefully everyone enjoyed it

and up next we're going to take a look

how we can use typescript in react all

right and once we're familiar with the

typescript fundamentals let's see how we

can use typescript with react before we

begin let me just mention that I assume

you are already comfortable with react

so things like components State most

common Hooks and some of the popular

libraries if you are confused about some

react topics please pause the video and

utilize some external resources since

our main focus is going to be on

implementing react with typescript

otherwise this part of the course will

easily turn into a react tutorial in

order to follow along with this part of

the course you will need a star project

which is the second folder in the main

course repo so if you have not already

done so get a hold of the repo either by

downloading or cloning it and once you

have the main repo on your machine open

the second folder in your text error so

get a hold of the

repo open up your text eror and then

just access the second

folder now it is a note app so same deal

we want to start by running npm install

first and also or you know what I'm not

going to set up such command because

here and there students complain that

such command doesn't work on their

operating system so first let's just run

npm install and then we want to go with

npm run run Dev and if everything is

correct again you'll have the

application on Local Host

5173 and this is what you should see on

the screen and if that's the case we can

move on to the next step all right and

let's start by taking a look at the

files and

folders as well as the assets I provided

so we have node modules over here this

is where we have all of our dependencies

we have the public one this is where we

can set up some public assets a source

folder again this is where we'll do all

of our work but in this case we're going

to be working with react so we'll create

components and all that cool stuff we

have the eslint file also a g ignore

again this just provides info what files

and folders are going to be ignored by

The Source control index HTML this is

where our root component is going to get

injected so for example if you want to

change the title feel free to do so a

package Json so in here you can take a

look what extra libraries I installed

and also we can see that we have a Dev

one so that spins up the dev server and

also same deal we have over here a build

command and before vit builds the

project what do we do we compile our

code then we have the good old

typescript configuration file and also a

few more configuration files for V and

also the node one now you'll also find

the readme over here and just like in

the first part of the course we will use

this readme to set up the challenges to

take a look at the examples I also

provided some links to useful resources

and all that cool stuff and first thing

that I just want to mention essentially

this project is a straight up beat react

TS boilerplate application the

difference I just added some assets to

it and removed some boiler plate files

that's it so if you're going to run npm

create V latest react typescript so this

is the name of course you can change it

then the double dashes template and

provide react DS effectively this is the

project you're going to get back and

like I mentioned before most of our work

we're going to do in a source

so let's just navigate over there for

starters just like

traditional react application we have

main DSX so this is where we inject our

app basically our root component into

that div with the ID of rot now also

you'll notice few Imports but we'll

discuss it

later I mean these are just Imports for

some extra libraries we're going to use

then we have the app DSX so this is

where all of our components are going to

meet you can also call this the root

component and we have a final and a

starter and the way I set it up notice

these are all the topics we're going to

discuss and this is going to be our

starting point and in here you'll find

the complete code so

essentially pretty much every time we'll

start working on a new topic we'll just

import the specific folder because if

you notice all of them have index DSX so

this will be the default import that's

just a note thing and then as we're

moving from topic to topic we'll just

change the path over here now for all of

them you'll just find this

standard component where I have few

heading twos and basically I'm just

displaying some text on the screen so

all of them pretty much will be the same

but of course once we're done the topic

there's going to be more files more

logic and rest of the good stuff and

just to Showcase how it's going to look

like let me navigate to app TSX we want

to go with import then let's come up

with the name in my case I'm going to go

pretty generic I'm going to say

component from and now we want to go to

a star forward slash and then again we

have all of these topics and as you can

see they are numbered so we'll start

with

return topic and then all the way to

tasks so let's go with 01 return notice

again we don't need to provide the file

because all of the folders have already

a index DSX and then we want to replace

it over here we want to go with

component and then render it on the

screen again at the moment it's not

going to change that much because we

haven't set up any logic yet and

basically as I'm moving from topic to

topic I'm just going to change over here

the path and then if you want to test

something of course you can import the

component from one of the final ones as

well now also something I want to

mention the idea with the react and

typescript is following if we want to

set up components basically react the

stuff we need to go with DSX so that's

the extension now if you just want to

set up some logic some good old

JavaScript logic just like we did in the

first part of the course we just go with

Ds so whether you want to set up some

hooks file or utils file or types file

that's the case you'll go with Ds but

the moment you set up the component you

want to go with

TSX hopefully I clearly explained how

our setup is going to work and if you're

looking at the other files over here in

the source one we'll discuss them

essentially as we progress with the

course content for example the hooks the

store so all of that is coming up and I

guess lastly let me just mention that

yes I did provide some index CSS just so

our examples look a bit more presentable

but again this is totally optional and

with this in place we can move on to our

next topic which is going to be

the component returns in react all right

so we have the correct import again

we're looking for Star 01 return so

that's where we want to navigate and our

first topic is going to be the component

return now let's establish a few things

for starters what are react components

they are functions correct and what is

the one thing that we know about

function returns and

typescript well it's the fact that

typescript infers the return type so if

I hover over notice how typescript sees

that essentially this is a component and

the return is jsx

element so what does that mean well if

for example I'm going to forget to set

up the turn actually typescript is going

to yell at me so notice once I save I

have red squiggly line in app DSX and if

we hover over we can see that component

cannot be used as jsx component because

it returns

void and few things I want to mention

first it's super helpful because when

you're working on a bigger project I

mean having no return sometimes can be

tricky to spot as far as the error go

and second one this is something that I

will probably repeat 10,000 times during

the second and most likely also the

third part of the

course code error is going to be your

best friend the moment you hover over

the squiggly line or in

general the events and state values and

all that it will immediately pretty much

give you all the info you need so in our

case let's say if we go back over here

and set up the proper return we can

clearly see that typescript infers the

jsx element which leads me to another

Point can

we explicitly write jsx element in here

as far as the component return yes it's

absolutely an option we can go over here

even though it's already inferred we can

say hey you know what I'm going to go

over here with jsx element we save it

and since in this case I am returning a

jsx element there's no issue pretty much

it's the same deal but keep in mind what

if in your component you decide that

you're going to return a string well now

it's not going to fly because now I

already have here an explicit return

where I say hey I'm going to return jsx

element and what about null What if I I

have some kind of logic and I'm going to

go with null again same deal we cannot

do that because we have explicitly over

here this jsx element now if you don't

have that typescript is smart typescript

can infer that hey in this case it can

be either hello either jsx element or no

so again this really comes down to your

preference one option you can simply let

the typescript to infer a type and at

least at the very basic scenario it's

going to help you to avoid this case

where you don't return anything second

option you can start hardcoding over

here explicitly what are you expecting

back from this component just keep in

mind as your logic changes you'll have

to adjust because if you're just going

to write all the time jsx element well

typescript is going to be confused so in

this case let me just hardcode it but

for most part I just let typescript to

infer a type so I'm going to go over

here with jsx element that's going to be

one option I'll say Hey listen it can

also be null and also well let's just

set up a string type let me save it and

now notice Ty script doesn't complain

everything's fine because I have the

explicit return and the options that I

have inside of the component match to

whatever I have over here in the list so

that's how we can set up component

returns in typescript all right and up

next on our list we have I believe props

so first let's change the path so we're

looking for 0 to props let's take a look

at

the browser yep we have react typescript

and props so looks like everything is

correct and essentially in here in the

component let's just provide some values

so we're going to go with something

generic for example name and the ID

which is going to be actually a number

so 1 two 3 and immediately once we add

those values typescript will complain

because again it's like setting up a

function providing the arguments but we

haven't set up the parameters so

typescript doesn't know what to expect

so let's navigate right now to our props

index DX and let's take a look at the

multiple options we have for props and

essentially the first one is the inline

one remember in react props are gathered

in this object which we access either by

just the structuring over here where we

go with the curly braces or we go with

props now I'll show you the other option

a little bit later for now let's just

grab the object the props object and

let's

explicitly take a name and the ID so

those are the two values we're looking

for but before we can do that since

we're working in a typescript yep just

like regular function we'll need to set

up the type and the first option we have

is basically set up everything in line

now I can tell you right away that it's

most likely not going to be your

approach especially for bigger projects

where you have components with bunch of

props because it's just going to be very

messy so yes in here it will start nice

and easy but in a second I'll show you

also another approach that we can take

so in here we just say Hey listen name

is going to be a string and the ID will

be a number and the moment we do that

typescript should be happy it just

complaining that we haven't essentially

used it yet now notice how everything's

fine in the component for some reason

it's complaining over here so let's try

to use these values and let's see

whether that makes typescript happy so

I'm just going to change it around I'll

say adding one now that one will be

equal to name and we're looking for our

name value and then the second one will

be Hing one and and we'll just provide

the ID so let's go with ID and then

let's access that let's save this and if

everything is correct we should see name

Peter and whatever ID

provided again we just go back to the

fundamentals section where we learn that

every time we have a function we need to

provide info to typescript what is this

function going to receive as far as the

argument and since props are essentially

arguments that we pass in when we

construct the

component we need to provide the type

annotations and what's really cool let's

say that we're using this component in

multiple places in our project if for

some reason I'm going to forget provide

one of the props notice how immediately

typescript is going to complain so I

won't have to realize this error at run

time as I'm building the project let's

say that I'm setting up this component

somewhere and I just forget that I also

need to provide the name typescript will

immediately let me know that something's

wrong and actually the same works if I

decide that the name is actually going

to be title I mean it's quite common to

have a component and you think that yeah

the name for the prop name is awesome

but then you realize that hey you know

what actually prop name should be titled

let's say I do that notice how

immediately in all the places where I'm

passing in the wrong prop it's going to

light up so again imagine scenario where

you have this component in multiple

places in your project immediately you

know that something is wrong again

something super super cool where you

don't need to run around like headless

chicken and then look for those

instances you'll immediately know where

you provided the wrong prop so let me

set it back to name and ID and up next

we're going to discuss alternatives to

inline type annotations okay so our

initial setup works but what if we have

a long list of props or let's say we

want to reuse these props well in that

case we can either set up the type or

the interface again this is the totally

up to you I'm going to stick with type

just because it's my preference I'm

going to call this component

props and in here we just want to

provide pretty much the same values so

actually you know what I can just cut it

out remove these curries set it equal to

and

then where I have my D structuring I

just want to set it equal to my

component props save it and since I

don't see any red squiggly lines I'm

good to go now also please keep in mind

that

alternatively you can just reference the

props so in here I can say yeah props is

going to be equal to component props

instead of the structuring name and ID

and then every time I want to access one

of the values I can go here with props

ID and props name again this really

comes down to your preference Some

people prefer the props option and some

people prefer this option as long as you

don't have the red squiggly lines as

long as typescript is not complaining it

does really come down to your preference

and the same goes for the type or the

interface so if you want to use the

interface over here you can definitely

do so if you prefer type it's definitely

an option as well and while we're still

on a topic of props let's also discuss

the special children prop which allows

elements and components to be passed

into other components so if I'm going to

go to app

PSX and set up my closing tag as well

and then let's say add a heading to with

a hello world typescript is going to

complain because I haven't specified

that I'm going to provide the children

prop now the name is exactly the same so

that doesn't change we just go over here

with children and yes we do want to

render it somewhere in our return as

well but now M dollar question what is

the type and essentially we have few

options we can hardcode it ourselves and

the type we're looking for is react node

and we can import it or we can just go

to react Dot and then react node so for

example this is one option we can take

where we go with react

Dot and then react node so that's the

type we have access to and the moment we

do that we fix the first error but

notice right now typescript is

complaining because since I set up my

children prop in the props component

it's also expecting the same thing over

here and one easy way how to fix that is

to just make this one optional just like

we covered through during the

fundamentals part so I can just go here

say that yeah children might be provided

or not and if it's provided then it's

going to be a react node now also a

quick side note just like with vanilla

JavaScript actually during development

everything is going to work even though

we have the error but please keep in

mind you won't be able to build the

project unless you change some

configurations and

allow the project to be built with the

typescript errors hopefully that is

clear so let me go back to this optional

property and let me show you another way

how we can handle the children prop

alternatively we can also import a

special type from react which is called

props with children so yes we have

access to a declaration file where there

is a type called props with children

which actually is going to handle

the children prop for us now in order to

import it we're going to go over here

with import now I will add this type

remember technically it's not a must

then we're looking for props with

children and this is going to be coming

from react and if we hover over we can

nicely see the type

definition and this is where I would

encourage you to stop the video and go

over this logic

and try to see whether you're able to

understand everything that's happening

under the hood since we have covered all

of these things during the fundamentals

part and again reading such type

definitions is going to be a good

practice for us not only to jog our

memory as far as typescript but also to

understand what is the specific type or

function or I don't know property

actually doing and if we take a look at

the type definition we can see that

props with children is a generic which

again kind of makes sense

because it's going to be used in a lot

of situations so there's going to be the

case where the component props has one

shape and then in the second component

the shape might be totally different so

again a very good use case for generic

Now by default it's actually going to be

set equal to to unknown so this will be

the default value and then notice how

they use this intersection type so

essentially whatever is passed over here

is just combined with what with children

property which is set equal to optional

so it might be passed might not and the

type here is going to be equal to react

node or it's going to be equal to

undefined so let's try it out

I think I'm going to leave this one for

your reference so let me just copy and

paste let me comment out first one over

here and then instead

of setting up the children property

ourselves we'll just go with props with

children and then we'll provide this

value over here so effectively it's

going to look like this we're going to

go with props with children remember

it's a generic and it's looking for that

type and the moment we do that as far as

the result notice we get back whatever

type we pass in and it's just combined

with this children property and with

this in place now I can go to the app

remove the heading 2 or provide the

heading 2 to the second instance and

everything is going to work and

typescript is not going to complain so

again when we work with children prop we

have few options either we can

explicitly provide the value of react

node ourselves or we can import the

props with children which essentially

does the same thing behind the scenes

all right and once we're clear on

component returns props up next let's

talk about state so first we want to

change the import and and this is

actually going to trigger some

typescript errors so I think I'm just

going to go with good old component for

now so let me render the component yep

typescript still complains because we

haven't changed the import so we're

looking for a 03 State and now we render

the component so now let's navigate to

this particular component and let's just

I guess set up heading two with some

kind of value as well as the button

because inside of the onclick we'll try

to change the state values so I think I

want to do that first and then we'll

worry about the actual logic so in here

inside of the div I want to go with

heading two I'll add one of the classes

so margin bottom is going to be set to

one and I guess I'm just going to leave

this one over

here then let me go with a button let me

remove this heading

to and let me add some classes just so

we have some basic styling so

BTN Center over here and then let's just

right click me and eventually we will

set up the on click let's not worry

about it right now this is what we

should see on the screen now I don't

know whether you remember but actually

we already covered sort of the Ed state

during the

fundamentals we talked about it when we

discussed the generics but let's go over

it one more time so yes we can nicely

use use state in react to control the

local state but if we take a look at use

State it's actually going to be a

generic so let's start I guess with the

import so looking for use State it's

coming from the react and let me just

hover over it notice this is going to be

the type definition it's a function it's

a generic and essentially we can either

pass in the initial state or we can pass

in the function and as far as the return

notice it Returns the value we provide

in the initial State and the function

that controls it so where I'm going with

this if we have just primitive values in

the use State you'll see that typescript

is very smart and it's going to infer

the type so for example if I'm going to

go over here with text and set text and

set it equal to my use State I don't

need to set up over here the type and

say that is going to be a string because

typ script is going to know that so if

I'm going to go here with shake and bake

and if I'll have our over text step

script knows that it's a string so

essentially whenever I will try to

update this value it's going to expect

the string and we can actually see that

over here if we go with on click and

let's not worry about how we can handle

events in react we'll cover that a

little bit later for now let's just pass

in our Arrow function just so we can

invoke set text and if I'm going to

provide a wrong type it's not going to

work so notice again as we're hovering

over what is the set State action

function looking for it's looking for

type string so it's going to be okay if

I go here with typescript yeah there are

no complaints but if I'm going to

provide the number immediately

typescript complaints again the logic

technically is going to work during

development I can navigate over here

press and technically I shouldn't have

any errors in a console nope everything

is fine but typescript is not happy with

me and the same is going to work if

let's say I'm going to set up the number

so let me navigate over here and instead

of text we're going to go with number

and set

number okay good and then we'll provide

the Primitive value over

here and you know what let me just

comment this one out for your reference

if we're going to go with set number

again we can see that set State action

function which essentially is a type for

this one for our set number function in

this case is expecting a number because

typescript is going to infer the type if

I'm going to provide it if I'm going to

say 23 yeah everything's awesome if I'm

going to go with some kind of string

value it's not going to work now it

doesn't stop me from explicitly going

over here and saying number I mean we

can still definitely do so but again the

whole point is that typescript is going

to do a very good job of inferring such

type now it's going to be a different

scenario if let's say we have empty

array as our initial value so let's say

we have over here a list then comma and

set list and we set it equal to use

State an empty array notice how

typescript essentially sets list to an

array but the type is equal to a never

and at this point we have few options

either we provide some values over here

so typescript knows what the type is

going to be so for example I can go with

hello but keep in mind there are

instances where you want the default

value to be empty array so I'm not going

to provide some random hello just to

make typescript happy so the solution in

this case is to use the generic approach

where we know that US state is in a

generic and we'll just say all right

yeah yeah it's an array but it's going

to be an array of strings and at that

point if I'm going to go to my on click

and go with my set list again my

function everything is going to be

awesome if I'm going to provide the

strings over here I'm going to go with

hello and maybe I'll also add over here

world so this is going to fly because I

have strings in my array however if

we're going to change this around and

we'll go with one and three notice

typescript is not happy because it's

expecting a type string so this is how

we can work with use State and

typescript by default typescript is

going to infer the type but it is a

generic and there's going to be

instances where we'll need to

explicitly provide the type that we

expect for the value and automatically

is going to be set for the set function

as well okay and up next let's cover an

example where we have a list of objects

now in my case I'm going to create nav

links but again the actual data is

totally up to you so I'm going to go

with naab links that will be my array

and I'm just going to provide some dummy

data and yes I will in the beginning

rely on the fact that typescript is

going to be able to infert a type so in

here I'm going to go with id1 then URL

I'll just type some URL so essentially

it's going to be some kind of string and

also text will be some kind of text so

some text okay let's save it then we

want to copy and paste so one and two

let's just change these values over here

two and three and I don't think think

I'm going to change any of the actual

values I don't think it's relevant now I

do want to set up the type type will be

equal to a link I'll say that ID is a

number okay awesome then URL will be a

string and then text will be a string as

well let me save it I'm not going to set

it up over here this is something we're

going to do later and now let's see how

we can work with that in our use state

so in here I'll call this links and set

links that will be my function name

we're going to go with use state for now

let's not set the type explicitly and

now let's just provide the nav links and

again typescript is super smart now it

knows that essentially links has this

shape and essentially we can go over

here where we have our own click we can

invoke set links let's say that I just

want to add it to an existing array so

I'm going to spread out all the current

links and I'm going to try to add a new

one if the values I provide don't match

the signature you'll see that typescript

will complain so if I'm going to go with

id4 then URL is going to be equal to

hello and then also a comma and I'm

going to go with I don't know what was

the last one I believe it was text right

if I'm going to say hello yeah

everything's awesome because this

matches the signature however if I'm

going to Omit text notice tapescript

immediately is going to complain because

the text property is missing so all of

this is nice the problem

becomes this is inferred and remember

when typescript infers something it

infers based on what on the original

value so for example if I just go and

comment this one out now notice

typescript thinks that yeah links

technically can be an array of objects

with this shape or with this shape where

text is actually missing so now if I'm

going to go here I'm actually going to

be successful so this is a good use case

where we want to go with our angle

brackets and we want to say

yeah we have these links over here but

actually the type is going to be

following it's going to be an array of

Link type so now typescript is going to

complain it's going to say Hey listen

you know whatever values you provided

they don't match so we need to fix it

over here and now the same deal is going

to be in our on click as well we'll have

to provide I believe it was our text one

now lastly I just want to mention that

technically we can avoid all of this

debacle pretty much if we just go with

our type annotation over here and we say

with the link then of course I'm not

going to be able to remove the property

but keep in mind there's going to be

some instances where you're not going to

be setting that data so again that's why

it's super useful to use the angle

brackets and to explicitly let

typescript know that the shape You're

Expecting is going to be following and

that way essentially later when you need

to update it's going to be very hard to

provide the wrong data and up next let's

see how we can handle events in react

for starters we want to change the

import so we're looking for

starter and the number four events one

the component is not expecting anything

because we just have the bare bone setup

with the div and all that and initially

I just want to set up two controlled

inputs one is going to be for text and

one will be for email and of course in

the process you'll see why we have two

of them so let's do that let's go with

use state that is coming from react

awesome then let's go with our text and

email and yes I will rely on the fact

that typescript can nicely infer the

Primitive types so I'm just going to go

with empty value

that will be my string and the same is

going to be for email let's provide the

name here and let's go with email let's

save this and now we want to set up two

inputs inside of the form again just for

better styling and all that I'll wrap

this into a section then we'll provide a

heading to I'll call this events

example and we want to go with our form

for now no action don't care about that

but we do want to add a class of form

and inside of it let's go with input

type will be equal to text let's just

add few classes here we're looking for

form input and margin bottom is going to

be set to

one since I'm creating over here a

controlled input I'm going to go with

value and on change so let me go with

value so that will be equal to my state

value so I'll set it equal to my text

and then also we have unchange which

essentially controls that value so we're

going to go over here with unchange in

here I'm going to pass in the arrow

function and remember we have access to

the event and now let's go with our set

text and let's pass in event. target.

value so again this is typical setup for

controlled inputs in react there's

nothing really

unique now we want to copy and paste and

we want to set up one for email the

difference we're not going to use the

arrow function we'll actually set up the

function reference so type yep still

equal to or you know what no it's

actually going to be email then the

class name for input yeah that stays the

same value will be email so this is

coming from the state and

also on change like I said there will be

a reference so you know what for now I

guess let's just remove it even though

most likely it's going to complain then

let's go with our button and Just for

kicks let's go with type and let's set

it equal to submit then let's add some

classes BTN and BTN block and let's

write over here

submit and actually this is something

that we covered previously when we

worked on the tasks application during

fundamentals you see in here when we

provide the arrow

function T script will nicely provide

the value for the

event as you can see it's react. change

event so that's the type we get from our

declaration files and it's a generic and

essentially we provide over here

the element the HTML input element and

this gives us a good clue what we need

to provide over here in the function

reference so if I'm going to navigate up

and I'm going to go with const and then

handle change function and if I'm going

to try to access the event typescript is

going to complain and it's going to say

Hey listen this is type any so for now

let's not worry about it let's just go

with event. target. Val just so you can

see that we can access that and let's

also go with our

set email and we want to provide the

same value so event. target.

value now let me navigate to my browser

so at the moment it's just complaining

because we haven't set the onchange this

is our form notice I can provide the

value but I cannot do the same for the

email and in order to provide the

correct type again we simply want to

reference what we have over here so

notice this change

event we want to go with event then

react Dot and then we're looking for the

change event and if we take a look at

the docs if we take a look at the type

definition we can see that change event

type is a

generic it's expecting a type which is

going to be the HTML element and the

default value is going to be element now

where we get back is Target and that

will be the intersection type between

the event Target and the type we provide

so now let's navigate back to our index

DSX and set up the angle brackets and

provide the correct element so we're

going to set this change event on H DML

and input element so now we have access

to the Target as well as the value so

this is what we need to do when we set

up the function as a reference again if

we just provide the inline

one everything is going to be set

already for us so now let me just

navigate over here and we're going to go

with on change and we'll set it equal to

anal change and with this in place that

typescript doesn't complain and also we

have the correct values in the browser

so let me go over here notice I'm able

to provide a value and the same is going

to be with my email okay and while we're

still on the topic of events let's cover

submit event and few things we need to

be aware of when we work with form data

API so let's say we want to handle the

form submissions we know that in react

there is onsubmit and same deal we can

either pass in the inline function or we

can set up the reference and just like

with on change event essentially if we

pass here the inline typescript will

right away infer the correct type if we

set up the function

reference then we'll need to do it

basically manually for

ourselves and you'll see that the form

event is very similar to change event

it's also going to be a generic and

we'll just need to provide the correct

HTML element and I think I'll right away

set up the function reference but you

know what before we do that let me just

mention that in between the videos I

added two

attributes one on each input and it was

the name attribute so in here I just set

the value for text and in here for email

simply because we will use the form data

in this video as well and in order to

access those values we need to add those

name attributes now I'm fully aware that

these are controlled inputs so

technically when we submit the form we

can access both of these values directly

but I do want to showcase some things

about form data and therefore I added

these attributes so if you want to

follow along I suggest you do the same

so like I said I'll right away set up

the reference let me go here with on

submit and I'm going to set it equal to

handle submit a function I don't have

yet so let me go with handle submit and

what is

typically the first thing we want to do

that's correct we want to prevent the

default so for now again I just pass in

the event and since typescript has no

idea what e I'm talking about it's going

to complain and it's going to say that

the parameter any so first let me just

set up the logic

prevent default and if we want to get

the type again we can always use the

editor as our best friend so notice

essentially we have over here the HTML

form element and then we're looking for

form event or you can pass in the inline

and you'll get the exact event type so

in here where we have the event we want

to go again with react or we just import

this type then we're looking for

form it's a generic and in here we

simply pass in HTML form and element and

now we have the correct type so now we

can use all the properties and methods

and typescript is going to be happy and

not going to complain now as far as form

data it's a nice interface to handle AE

if you have bunch of form inputs and you

don't want to deal with controlled input

so you don't want to set up the state

variables you don't want to set up the

on change as well as the value then it's

pretty straightforward just set up the

form add those name attributes and

you're good to go once you submit the

form you'll have access to it by

creating a a new instance of form data

so in here we want to go const form data

we want to set it equal to new

form data so this is right away

available to us we don't need to do

anything and then if you don't work with

typescript essentially we have two

options we can either go with

event. current Target and notice how

with

typescript we can do the same typescript

is not going to complain however

if we're going to go with event. Target

which again we can do without typescript

actually it's not going to work if we

use typescript so let me just comment

this one out for your reference and

actually I'll use this one later on

anyway but if we go here with

event.target

it's not going to fly so typescript is

going to complain now way around that is

to basically go with HTML and then

provide form element so we just add this

type assertion where

yeah we're looking for event. Target but

we say that Hey listen this is going to

be actually a forum element now if we go

with current Target typescript is smart

and it can see that we already have this

element over here so let me like I said

come in this one out and actually use

the current Target and then one more

gotch about form

data potentially the values could be

null as well and we need to handle that

so how does that look like well for

stars let me just showcase how we can

nicely access all of the values so if we

go here with object dot then from

entries so now we just need to provide

deform data and we'll get access to all

of the values so if I go with data then

let me refresh and provide some values

so some name and

email at

email.com let's see where we get back

once we click on submit notice we'll

have this object and even if we have 15

inputs we'll have a object with 15

properties with all of the values over

here and as far as the gacha well let me

first create a type just so we can

clearly see that so let's say we have

over here type person is equal equal to

and then name and that will be equal to

string so pretty straightforward type

and then let's go here with const

person let's set it equal to our person

type and we're going to go here with

name and now let's get the value now

it's going to be the same for the object

over here for the text property inside

of this object but first I'll just

showcase what happens if we use the form

data. getet method which is available to

us so let's say I only want to get the

text value I can always go here with

text equals to form data then dot get

then we need to provide the name and the

names need to match so let's say in this

case I want to access the

text notice the value that I'm getting

back either it's going to be form data

entry value type or it's going to be

null now why do we care about that well

if I'm I'm going to set my name equal to

a text typescript is not going to be

happy about that it says Hey listen

potentially it can also be a null and

you cannot

assign this value to a string so the way

around that is to again use the type

assertion where essentially we go with

as and then we set it equal to string

and here again I'm telling typescript

that I know more about the project where

yeah maybe this can be known but in this

case I know for sure that value is going

to be correct because I know that these

two values match and now notice how

everything works and the same is going

to be over here let's say if we go with

data. text remember that was the

property name again it's not going to

fly so in that case we again need to go

with as and then string and now

typescript doesn't complain so just to

recap whenever we set up events in react

if we provide the inline

function everything is inferred as far

as the event type so there's really not

that much difference between typescript

or not typescript however if we set up

functions as the

references then we'll need to provide

the correct type for the

event and there are two things things

that we're looking for we first need to

grab the correct event type and also

we'll need to

provide the correct HTML element since

most of these events are actually

generic now if we want to get the quick

suggestion we simply can set up the prop

on the element and then provide the

inline function and the moment we do

that we'll get a nice suggestion with

the correct event type and the correct

HTML element okay and up next let's work

on a small Challenge and I think it's

going to be

easier for me to

showcase the requirements so

first let's set up the import but in

this case we're looking for the final

folder so all this time we have been

importing from the Star this is the case

where we will import from the final one

so let's go with Port let's come up with

a name in my case it's going to be

component from then we're going to go in

the final one more specifically

Challenge and then we'll set up two

instances so first we're going to go

with component we'll need to provide the

type as far as the values notice we have

two options we can either go with

Advanced or basic so let's start with

basic

then if we have basic we'll also need to

provide the name in my case I'm going to

go with Susan let's close this component

and let's set up another instance where

we're going to go with component then

type now if we go with Advanced now

we'll need to provide more values not

only we'll need to provide the name

which is going to be Anna also we'll

need to provide the email and let's go

with Anna gmail.com and if we take a

look at the browser you'll see something

like this so so this is going to be the

look for the basic one and this is going

to be the look for I believe the name

was Advanced so here's the challenge

create a component that has following

features if we provide type basic we

only look for

name however if we provide type Advanced

we also need to provide email so for

example if I'll try to set up ADV

Advanced without the

email typescript is going to complain

and also based on a type notice how we

have different looks so for the basic

one we have this one and then for the

advanced one we have a different look

now a tiny hint as far as the classes in

here in CSS you're looking for alert and

alert danger and success so this CSS

part is totally

irrelevant technically you can skip it

for example you can just add a red text

or something along those lines for one

of the classes the general idea is to

create a component where based on that

type we are

first providing different sets of props

and if we don't then we get the error

and also we get a different look so try

to work on this Challenge and in the

upcoming videos I'll show you my

solution okay and first let me show you

a typical react solution prior to

typescript we'll also take a look at the

potential issues essentially we won't be

able to complete the challenge and in

the following video I'll show you a

proper typescript solution so first let

me comment some things

out first one the import and then these

two so I still want these for your

reference because they will help me to

showcase the potential issues and now

let me grab the import component from

and now we're looking for the starter

and same folder so we're looking for the

challenge and we want to render that

component somewhere so let's render the

component let's take a look at the

browser so now we have react and

typescript

Challenge and initially our approach

could look something like this where we

know that we need this type prop we also

know that we need name and email and we

know that based on that type we will

display one set of classes and if it's

the opposite then we'll display a

different set so let's navigate first to

starter and then index I guess we can

right away set up the type over here or

interface that is totally up to you I'm

going to go with type profile card props

three properties so we start here with

type

just because I enjoy it so much I'm just

going to go with the literal type so I'm

going to say yeah the possible values

here are basic or they're going to be

Advanced then there's going to be a name

which is a string and also we'll set up

the email which also will be a string

cool cool cool and awesome start then in

the component I'll say yeah there's a

prop subject and actually it's going to

have this type so profile card props

okay cool then let's gather all of these

things so we're looking for type name

and email and that is equal to our props

typescript is complaining because we're

not using these elements and you know

what before we set up the return let me

just set up the logic for the class so

essentially if the type is basic I want

to use the success one and if not I'm

going to use the danger again just to go

back notice in the index we have this

class for alert so this is just going to

add the padding and or radius and all

that and then based on this class so

either alert danger or alert success

we'll just have the background color and

color and yes of course we can set it up

over here in the return but I'll do it

above since in my opinion it's going to

be easier to see what we're doing so

alert type is going to be equal to type

then either basic or Advanced that is

totally up to you and I'm going to go

with success since that's the class name

and yes they do need to match and then

based on this one I'll set up my class

name so I'm going to go with const class

name and we'll set it equal to alert so

that's my main class and then alert iph

and now let's access the alert type so

hopefully it's clear that if it's going

to be equal to Advanced essentially not

basic then the value is going to be

danger if going to be equal to basic

then essentially the value will be

success and as a result our card is

going to look different so in here we

want to go with

article and then let's add a class name

so let's access our variable over here

or constant I guess more properly and

then let's just access both of the

props so the first heading two is going

to be user so we're going to go user is

equal to our name prop now when it comes

to email it's going to be a little bit

different simply because we only want to

display the email if the type is equal

to Advanced correct so in my case I will

only display the email if it's

provided now we can set up turn operator

or we can use the good old hand operator

and I think I'll stick with that one

because in my opinion in this case it

doesn't really make a difference so

let's look for heading two then let's

set it equal to email and now we just

want to access the email prop okay good

we have everything in place now let's

navigate back and let's provide these

values and you'll notice something

interesting we will only be able

to display the advanced component let me

showcase why so let me go here with type

we're looking for

advanced then let's go with name again

doesn't really matter what we provide so

I'm going to go with Susan and let me

also provide the email over here let me

go with Susan at

susan. let me save it everything looks

correct but notice if I'm going to go

here with the basic and just omit the

email not going to be successful why

well let's take a look at our type

typescript is expecting this email one

so if I'll copy and paste over here and

if I'll say yeah the type is going to be

basic and actually I don't want to

provide the

email typescript is going to complain

it's going to say Hey listen I still

need this email and technically you can

make an argument okay well I could

provide email over here and just provide

empty string and even though it kind of

works you have to agree that this is

somewhat

clunky

my goal is to have a component where if

I provide this type Advanced I am

looking for email and if it's actually

type basic I'm not even looking for this

prop that's my

goal now you could make an argument that

we can go back and make this one

optional over here and yeah technically

it works for the basic one right now but

what about the advanced one so now this

technically is optional as well so if I

remove it typescript doesn't complain

but if I navigate back I'm not showing

the email in my Advanced user card as

you can see in both of the cases we have

issues we don't have the

setup that we're looking for and

therefore in the following video we will

cover a proper typescript solution and

since I know that I'm going to get this

question a lot let me just answer it

here no adding following logic to our

component is not going to solve the

issue so yes

definitely not only we can check for

email we can also check for type and set

up the tary operator where if the type

is equal to advaned then we display the

heading to with an email and if not we

go with null but notice our component so

for example if I have the advanced one

yes it nicely requires the email and

once I provide everything is

awesome but it's going to be the same

thing with our basic one so since the

prop is present I need to provide it and

yes I can still provide the empty string

but remember that's not my solution

that's not what I'm looking for I don't

want to randomly provide these empty

strings and if we change this one around

to optional property same deal

now if I go to app DSX and remove both

of these values over here notice

essentially the first card is correct

but the second one has empty email value

so yes even though this one looks like a

better solution essentially it has the

same

issues as the one that we used before

where we checked for the email all right

and once we have covered the issues with

our initial setup

now let's complete the challenge

by constructing a proper typescript

solution for starters I do want to

remove these ones so I want to start

from the scratch and essentially in here

we want to create two types so our

component actually is going to have two

types so the first one is going to be

basic one and second one will be

Advanced so we're not going to use this

literal type over here we're actually

going to hardcode it equal to a basic

and since there's going to be two types

I'll also name this one basic profile

card props now let me copy this one and

in here we want to remove the

email and it's not going to be optional

anymore so if the type is Advanced if

we'll have this type then we'll look for

all of these properties so type is going

to be equal to Advanced name String and

email string now for the basic one we'll

only have type basic and name type is

going to be a string now where we have

the component I'll actually create

another type I'll say profile card props

and this will be a union type with basic

profile card props and the advanced

profile card

props and in here we're actually going

to set up to return based on a type so

for starters what two properties we can

always access well it's the type as well

as the name correct because keep in mind

we only have access to email if the type

is equal to Advanced profile card props

so therefore we're going to look for two

properties that are always going to be

there so name and type and now

essentially we want to set up our return

where we're going to go with well if

type is equal to basic one of the

potential values then we'll have one set

of elements if not well then we'll

return prey much the other card so let's

go here with the return we're looking

for the article so in this case we don't

need to set up that logic to add classes

based on type we simply we want to go

with class name alert alert

success and then inside of the article

we're just going to go with heading two

user and we'll access the

name so let's set it up over here and

then if the type is

Advanced basically our second option

you'll see that we have access to props

that email so let's go here with the

return and as a sign you can actually

structure it here as well so in here you

can go with email and actually

typescript is not going to complain and

it sees that email is actually a string

simply because if the type is basic okay

we have one return so it knows that at

this point the email has to be present

now in my case I will use the props that

email again doesn't really matter which

way you pick so we want to go over here

with article then let's add the classes

now we just want to provide the

different values so it's not going to be

success it's actually going to be a

danger one and then inside of the

article we're going to go with heading

two we're looking for user then we want

to access the name just like before and

we'll also add the heading two with

email and then we'll grab the props that

email so now let's navigate to app and

if everything is correct if we type

basic we only need to provide the name

and we'll get the correct look however

if we go with Advanced we'll need to

provide both of those values so if we go

with component type notice we have basic

or advanc so those are our two options

if we go with basic we only need to

provide the name so now we have property

name is missing okay good it's provided

and notice how we don't need to provide

an email here with an empty value no

that script is Happy everything's fine

we have correctly a basic user card now

if we're going to go here with component

type and we'll set up the advanced now

it's looking for name and email so one

by one let's set it up we have name

again let's go with our Anna and email

and let's just provide the value Yep

looks about right hopefully everyone

enjoyed the challenge and we can move on

to the next topic all right and up next

let's see how we can use typescript with

context API before we begin please keep

in mind that we will write bunch of the

boiler plate code meaning don't get

overwhelmed by the amount of code since

you'll be able to take it from Project

to project and second at this point in

time context API is not as popular

anymore so if you don't find these

examples useful don't stress about it in

fact if you don't use the context API at

all in your apps feel free to skip the

following videos for context API I did

prepare two examples the very basic one

with just one state value and a more

complex one with more bells and with

just so we can cover all the topics step

by step so let's start just like with

the previous examples where we want to

import from the star in this case we're

looking for the context one and in this

case we'll create two files so one is

going to be for context and essentially

in the index one we'll access the

context now if you work with context API

before you know that technically we can

wrap the app component in context we can

also set it up in the main

DSX so there's tons of options but in

this case I just decided to set up

everything in the context just so it's

easier add it to the final one and leave

it for your reference so don't be

surprised if in this example we'll have

two files so for stars we're looking for

component so this is coming from where

we're going to final and then we want to

look for context again let's render it

somewhere here on the screen the

component one and let's navigate to our

06 context one let's create a new one

and the name is going to be context DSX

in here we need two Imports and you know

what actually I'll set up the third one

as well since we'll use it in the

following example so we're looking for

two functions create context one and

also use context since we'll set up the

hook as well and then lastly in the

following example we'll use the use

state so I'll add that import here as

well right away and for now let's just

create a new context now as far as the

naming you'll notice that I keep using

this theme and it's simply because the

following example is going to be for the

theme and I prettyy much want to use the

same names so we'll just build on this

example that way we don't need to type

too much so theme

provider and let's call this context

let's invoke create context now this is

going to be generic and the difference

between normal react and react with

typescript is that we'll have to provide

the default value so in this case I'm

just going to go with undefined let's

imagine that we don't know what the

context is going to be then we want to

set up a component which is actually

going

to wrap all of our components and

provide the context so we're going to go

here with

theme provider and if you're familiar

with the context API you know that this

component normally is looking for

children so it's looking for the

component since it's a context provider

so in here we'll definitely need

children and we know already that as far

as the type we can either use the type

provided by react or we can just go with

react and then do and react node

somewhere here now as far as the logic

here's where we want to go with return

and we'll just set up one value so we're

looking for theme provider context it

has the provider component so we go here

with the provider and then we want to

wrap the children we'll go here with the

children and notice how typescript is

complaining because we do need to

provide the value now once we provide a

value you'll notice that typescript is

not going to be happy with create

context setup so for now let me just

showcase the basic example let's say I

provide over here the hello and the

moment we do that notice we right away

get the red squiggly line and the error

message says well you cannot assign

string to undefined so this was okay

initially when we were creating the

context we could say all right so it's

going to be undefined but now typescript

is complaining and in order to fix it

create context is a generic and in here

we'll use the type Union first we'll

provide what is the eventual value which

will be a string here and we'll also go

over here and say that it can be

undefined so this will be our initial

value and then this will be our eventual

value So eventually we'll have this

value equal to string and that's why we

have over here this type I'm purposely

keeping still this undefined because

it's going to be super useful once we

set up our custom hook so even before we

wrap any of our components I also want

to set up a hook called use theme again

I'm just going to keep these names since

we will use them in our following

example as well and in here we want to

invoke use context which is looking for

the theme provider context essentially

any context so let's set up this one

context is equal to use context and

we're going to go with theme provider

context and now if the context is

undefined I actually want to throw the

error now when the context is going to

to be undefined because at the moment we

can clearly see that actually we do have

a string well this context could be

undefined if let's say we're trying to

access this use theme but the component

where we're using the hook is not

wrapped in the theme provider context

and in my opinion it's a good setup

because that way we immediately can see

that there is an error and you'll see

what I'm talking about in a second if

this is confusing so I'm going to go

here with context and if it's actually

equal to Define I'm going to throw the

eror and if everything is correct then

we'll return the context so say here

return context but before that we'll go

throw new and error and let's just

provide some kind of error message my

case I'm going to go with use theme must

be used

within the theme provider let me save it

over here and now let's navigate to our

index one let's import both things the

hook as well as the theme provider and

now let's set up the parent component so

we're not going to export this one as

default actually there's going to be a

parent component where we'll have our

theme provider so first let's start here

with use theme okay yeah that's coming

from the context and I also want to grab

the theme provider and then let's set up

the parent comp component again this is

just to demonstrate how we can wrap

components please keep in mind that

typically you'll do that in the app or

in the main DSX so we go here with

parent

component that's our function basically

our component and as far as default one

I actually want to export the parent

component not the component and then in

here let's go with theme

provider and then inside of it we want

to place the component essentially this

one and once we nicely wrap the

component we can actually go over here

and I can go with context go with use

theme so that's my hook this is how I

can access the values and basically if

we log over here and provide the context

if everything is correct we should see

that value hello in the console so now

let's navigate to the browser and H this

looks

interesting so it looks like I'm

grabbing the file from the final one so

let me navigate back yeah we're not

looking for final my bad so we're

looking for the starter in this case and

once we do that notice the value is

hello and essentially it matches

whatever we pass over over here in the

value prop now of course normally this

is going to be more complex for example

you could have here an object and name

is going to be equal to something let's

go with hello same deal now I'll just

need to go back over here where we

create the context and just provide that

eventual value so again this is

undefined this is the default one and in

here I can say that yeah there's going

to be an object and the property is

actually going to be string so notice

now if we navigate to the console we'll

see this value instead and the reason

why this line of code is so useful is

because if we navigate back and for

example we forget to wrap everything in

our theme provider basically let's say

that we are trying to access our theme

context without wrapping the theme

provider and I'm just going to simulate

that by returning a component notice how

immediately I'm going to have the error

in a console and not only that it's

going to be super helpful where it's

going to say hey us te must be used

within the theme provider so this is

going to give me a super good clue what

is wrong with my current code and of

course now I just need to go back and

wrap everything nicely in the theme

provider so let me remove move this one

and now again we're good to go the main

deal over here when we use tapescript we

will need to provide what is the

eventual type for our value prop over

here and we can simply say that yeah

initially it's going to be undefined and

then

eventually whatever we set up in a value

we'll need to provide the type over here

and since the theme provider is always

going to be looking for children so is

going to be looking for components

therefore we'll need to provide a type

for a children prop as well all right

and now let's work on more complex

example please keep in mind that this

code is going to be available in the

readme just in case you ever want to

reference and also in the final one

you'll find this basic context and basic

index

TSX and essentially this is the code

that we set up in the previous video

because in my case I will modify my

existing code right now so for starters

I'm going to go here with type and theme

and I'm going to go with literal types

so we'll provide

light uh we'll also provide dark and

we're going to go with system and

essentially we're building here a theme

context provider so let's say in our

application we want to toggle between

the light and a dark theme and we want

to do it globally therefore we're going

to set up the context provider now let

me navigate to theme provider and

essentially I'll set up over here a use

state so I'm going to go with use State

and we know that it's a generic and I'll

say

yeah the value is going to be string but

actually it's going to be type of theme

and eventually we will provide the

default value let's not worry about it

right now and let's just go with

theme and as I not I do need to provide

the square brackets and we're looking

for theme and also a set

theme so we have these values over here

and as far as what I want to pass down

instead of this name hello I'll actually

go with theme and also a set theme so

now of course typescript is going to

complain because this doesn't match

whatever I have have here in the create

context so let's fix that let's set up a

type for our state which actually

matches whatever I have in the value so

we're going to go here with type theme

provider and let's say State props State

that's totally up to you I'm going to go

with theme and that is equal to a theme

over here so theme type and also a set

theme and essentially we'll just say

that that it's a function which is

looking for a theme and type will be

equal to a theme and it doesn't return

anything so we

simply provide void over here and

instead of hardcoding the object with

the name property which is a type string

we're going to go with theme provider

State now in this case it's complaining

because it says well theme can also be

undefined and we have multiple ways how

we can fix that either we can provide

the value like so so I can just say yeah

the default value is going to be dark

light or whatever

or in my scenario I'm actually going to

add one more property in the props and

therefore I will set up a separate type

so I'm going to go type theme

provider and let's call this props and

we'll look for two things first one is

going to be children so this one is the

same so react Dot and we're looking for

react node and also I want to set up the

default theme so let me add over here a

property default theme I will set it

optional and I'll actually set it equal

to type theme so it's going to be

optional but it needs to match one of

these values so light dark or system one

and where I have the theme provider I'll

actually remove the hardcoded one and

add theme provider props and in here

let's go with default theme and I will

add some default value which is actually

going to be a system and now at the very

end I'll go over here and provide

default theme and pretty much this

concludes our theme setup so as you can

see once we understand how we can set up

a basic context with just just one value

it's pretty easy to set up a more

complex one so now we just want to

navigate to index DSX and we want to

change our component around so this one

will stay the same and of course if you

want to test it out you can provide over

here the default value and all that

that's definitely an option but in my

case I just want to grab the context

with a theme and I also want to set up a

button which I'll use to change the

theme so in here right after this react

and typescript so I guess I'm going to

leave that I want to set up a button and

remember now in our context we have

multiple things not only we have theme

system but we also have this set theme

function so I want to try to invoke the

set theme on a button click just so I

can see whether my functionality works

so let's add over here a value I guess

I'm going to go with toggle theme and

then also let's add the onclick so we're

going to go over here with onclick let's

provide the arrow function and I'm just

going to check what is the value if the

value is equal to dark then I'll set it

back to system and if it's actually a

system one then I'm going to go with

theme dark so let's go here with context

Dot and we're looking for theme then we

want to check the value notice how we

right away get our nice suggestions I'm

going to say if it's equal to dark then

I want to set it to system context then

set theme and we provide the system one

then we return like so now if it's

already a system one then we just want

to go with context set theme and we

provide over here the value of dark and

you know what I also want to add some

classes here so let's go with BTN and BT

and Center let's save it now I have my

button and pretty much every time I'll

click on it I'll change this value now

we haven't set up any CSS so nothing is

going to change as far as the background

but notice as I'm clicking I'm actually

changing the value in a state so that's

how we can set up context API with

typescript okay and up next let's see

how we can use typescript with use

reducer hook and just like context yes

it's not as popular anymore since we

have options like Redux toolkit and Zoo

stand but you still might encounter it

from time to time and therefore I

decided to add it to the course just

like before we want to start in app DSX

hopefully this time I'm importing from

the correct folder so let me go with

star and now I want to go to Red

producers okay let's save it let's see

okay at the moment I have react and

typescript reducers looks about right

and this is the case where I do

suggest navigating to a readme and

basically we want to get some star code

because I really don't think that it's

going to be beneficial to type this

together so essentially go to 07

reducers and you're looking for this

function so this is what you want to set

up in your comp component not the app

DSX make sure you navigate to the

starter 07 and we're looking for the

index one this is what you want to paste

it over here and essentially this is

what you'll see in the browser so we'll

have increment decrement and reset so at

the moment nothing is happening we just

have some console logs over here and

also we have this set status to active

and inactive so basically our state is

going to consider consist of two things

so there's going to be some counter

value and also we'll change the string

value of active and inactive just to

Showcase how it works and our goal

essentially is to set up the US reducer

hook and also set up the reducer initial

State and all that cool stuff so now

let's navigate back to the component we

want to go with const and this is

returning two things State and also a

dispatch and we set it equal to use

reducer so we import that and it's going

to look for counter reducer so some kind

of reducer function and also initial

state so first let me just provide these

values please don't import them from the

final one we'll just go here with

counter reducer and initial state so

I'll set up both of these values now of

course we don't have them in this file

this is why we want to go to the folder

and we want to create a new one so in

this case I'm going to call this reducer

TS again if we have a component file yes

we go with DSX but if it's just going to

be a Javascript file then we just go

with TS so let's set up reducer yes and

let's start with the initial state so

this is something we're going to export

we're going to go with initial state in

a second we'll set up the type for now

let's just go with count which is equal

to to a zero and then status the initial

value will be pending but this is where

we'll change it to active and inactive

so now let's set up the type for this

one so export type counter State and in

here we have two values we have count

which is type number and also we have a

status which is equal to a string so now

we just want to go here where we have

the initial State and set up our type so

counter State okay awesome so we're

exporting that I guess we can now go

over here with import and we are looking

for our initial State and this is coming

from the same folder so we just look for

reducer so now we just need to set up

the counter reducer and for now it's

simply going to be a function and if you

know the reducer so it's looking for the

state as well as the action so what is

the state and what are we going to do

with that State and for now we're just

going to return that state so we're

going to go here with export then const

counter reducer so that will be the same

name and we'll set it equal to our

function our Arrow

function as far as the parameters this

is what we're looking for the state

which is actually equal to a counter

State and action and for now let's just

set it equal to any of course as we're

working on a functionality we're going

to fix that and and as far as what we

want to return from the function we're

going to go with counter State and then

inside we're going to go with a return

and state so pretty much for now we're

just going to grab the state and we'll

return State as it is so then back in

the index the

SX not only we have initial state but we

also have the counter

reducer so in the upcoming videos we can

start working on the functionality and

once we have setup in place I guess

let's start by displaying the value from

the state so at the moment we're

hardcoding the count as well as the

status but keep in mind that in here we

already have some initial values so

let's just access

those count is going to be equal to the

state that we're getting back and notice

how we have these two properties and in

this case I'm looking for the count and

the same is going to be for the active

one instead of Ive actually is going to

be equal to a state and then the status

let's save it notice now we have count

and also we have the pending one since

that's my default value and I think I'm

going to start with these ones so we

want to set up few types one for

increment decrement as well as the reset

one and we're going to start by setting

up a type and I'm going to call this

update count action so that will will be

my type over here so let's set it up so

type update count action and here I'm

going to go with the literal one so

either it's going to be increment

decrement or reset so type increment

then Union we also can have decrement

and also we can reset the value over

here and now I'm going to create another

type since there will be one for the

status one but technically I mean if I

would only have the count over here so

if I wouldn't have functionality to

change the status I can simply go to

update count action and set it equal to

my action so that will be my type but

since there's going to be more logic I'm

going to go with type and then

counter action and that one will be for

now equal to update count action so now

where we have the action in the counter

reducer we want to go with counter

action and now let's set up our logic

where inside of the counter reducer

instead of returning the state we're

going to go switch statement and we want

to go with action and type notice again

we have these potential three values and

then

based on the actual value we'll do some

logic over here so first let's set up

the default one and and let's say that

by default we'll just return a state we

say State over here and

then as far as the cases let's go with

increment first so that's going to be

our first case and then we want to go

with return and we want to pretty much

spread out the current state so we only

want to update and then count is going

to be equal to State DOT and count Plus

one and prettyy much we want to do the

same thing for rest of them so the

second one will be decrement case

decrement as you can see we only have

two options at the moment so decrement

and we just want to change this around

where instead of plus one we're going to

go with minus one and then lastly we

also have the reset case reset and if

that's the case just want to grab this

State and basically set the count equal

to zero now in order to invoke we need

to use the dispatch and we need to pass

in the correct type so instead of just

logging it over here we want to go

dispatch and then we need to provide

what is going to be the type and as far

as the increment one it's over here and

we want to repeat for decrement the same

same

dispatch type and then decrement and

then at the very end we also have the

recet one so as you can see the biggest

difference is that now we have a clear

control over the action type so usually

this was the biggest pain points where

you could provide some random value once

we use the typescript it's actually not

the case anymore we clearly have a list

of values that we can provide and we're

not going to provide anything random so

notice now I navigate over here to the

browser and I have these three working

buttons okay and let's also see how we

can handle the action where we have the

payload so with our counter pretty much

we're only handling the type correct and

then based on that we control the state

value but we can also pass in the

payload and for starters let's set up a

type for that so we're going to go with

set status and let's call this action as

well in here there's also going to be a

type so this property we definitely need

to

provide and as far as the value I'm

going to go with set status and then

when it comes to payload I'm just going

to go with few options and again I'm

going to use my literal type so I'm

going to go with

active and also it's going to be equal

to inactive then we want to navigate to

our reducer and let's set up the case

where we're going to go with set and

status and as I note before we do that

actually we need to add this set status

action to our counter action to our

counter action type because this is how

we're checking actually in the reducer

so let's go with set status action and

now notice how we're going to get some

nice suggestions so if I go over here

with case and then set status now we

just need to decide what are we going to

do and in my case I'm going to return

state so that doesn't change and as note

there is a error over here and now we

just need to update the I believe what

was

the value the status one correct so in

the state there is a status one and

we're just going to set it equal

to action and payload so we'll set it

equal to one of these strings over here

so now we want to navigate to index

DSX and where we have the console logs

to active and inactive same deal we just

want to dispatch it type going to be

equal to and we want to go with set

status and then we will need to provide

the payload as well so in here let's go

with payload and this will be equal to

active one I guess that's going to be

the first button and now we want to copy

and based and just change these values

around so instead of active we're going

to go with

inactive yep if I provide the correct

value everything is awesome so now let's

just navigate to the browser and not

only we can control the counter but we

can also change these values so we can

also pass the payload and at the very

end let's also not forget about the type

never so let me navigate back to the

reducer and we can see over here that by

default we return the state which

technically is okay but just keep in

mind we can add some kind of type over

here and this is going to fail silently

so for example if I'm going to add

another type over here I'm going to go

with something random if I'm going to

dispatch it I mean it's going to go

through my cases and essentially I'll

just get back to state so the problem

with this one is that it's very hard to

catch this error and therefore in here

where we have the default actually we

want to add some logic where I'm going

to go with con on handled action type

remember type is never and we're going

to set it equal to an action and now

notice how immediately it complains

because effectively there is another

type the moment actually it's random one

over here and unless we handle it so

unless I go over here case and then and

random and then decide what I want to do

for example return and then dot dot dot

State unless I do that there will be a

error and what's really cool that it's

actually at buil time so not at runtime

so now let me remove this example over

here and let's just complete by throwing

a error so let me go with throw new

error and let's provide some error

message and once we have this one in

place now we can remove it and not only

we'll be able to catch the error but

also if for some reason we add type and

we dispatch it there's going to be a

super helpful error in the console which

right away will lead back to the counter

reducer all right and up next let's see

how we can fetch data in react with

typescript and we'll actually look at

two options the good old use effect and

fetch API and my current favorite one

the react query with axio

please keep in mind that this section

will only make sense if you watch the

fetch data fundamentals part since I'm

not going to repeat things like Zod

setup and the actual need for types just

like in the previous examples we're

going to start in the app TSX where

we're looking for component and more

specifically the star and then 08 fetch

data and then if we take a look at the

browser this is what we should see we'll

also use the same URL like in

fundamentals so basically will fetch the

same doors from my server and therefore

I suggest just navigating to read me

you're looking for 08 fetch data and

just grab these two lines of code so

we'll utilize these hooks in a second

and then also here's the URL we're going

to use so grab it over here then we're

going to navigate back and I guess let's

just start setting up the state values

now eventually we'll set up the tors

but at the end of this video I'll show

you why we're not doing that right now

why essentially we need a type first and

then let's set up two more State values

we're going to have one for is

loading and then also set is loading so

this is going to be true while we're

fetching we're going to go with use

State and we can provide angle brackets

here it's definitely an option or we can

just type over here the default value

and then typescript is going to be super

smart and it's going to figure out that

essentially this will be a Boolean so I

guess let's just go with that one and as

far as my default value it will be set

equal to false then we also want to go

with is error and we're going to set it

to set is

error so that will be our set function

and here we're going to provide the

angle brackets and there's going to be a

union type so either it's going to be a

string so if there's error I'm actually

going to use the error message or or it

will be null and null will be my default

value so I'll just provide null over

here then the good old use effect and we

want to set up the fetch function inside

of it so let's go with our use effect

let's provide the Callback function

we're just going to invoke it when the

component mounts and inside of it let's

set up our fetch data which will be my

the same function so fetch data and

let's set it equal to a

sync and as far as the functionality

since it's a sync we want to nicely wrap

everything in the try and catch and also

we want to start by setting is loading

is true so while we're fetching we'll

set it equal to true and then at the end

we'll set it essentially equal to false

and you know what actually in here let's

go with finally so here we'll just set

it set is loading and equal to false so

whether we're getting the error or we're

successful doesn't really matter at the

end of the day we'll always set it back

to false now in the tri block this is

where we want to construct our fetch

which again we can right away start

using because we have access to it so

we're going to go here with await fetch

then we provide the URL then fetch API

has that Quirk where effectively we do

want to catch the 404 errors as well so

I'm just going to check for that okay

properly so if I have some kind of error

I actually want to throw it over here so

throw new error which of course will

right away lead to a catch block and

then as far as the message I'm just

going to say failed to fetch doers and

after this condition I want to set up my

raw data since eventually we'll set up

Zod as well and for now let's just go to

response.

Json and then let's log this data so

we're not going to set anything in the

state and when it comes to a catch let's

again construct that message so we're

going to go with message and this one is

equal to error and we're going to check

whether error is the instance off and

error and if that's the case then we're

going to go with error and

message or there was an error so

something generic and we also want to go

here with set is eror and we want to

provide our message so that should do it

we just want to invoke it over here and

we want to set up three returns so at

the moment we have one so basically this

is our standard return and now let's

check for loading let's check for is

error and then let's see whether we

actually are getting data and then we'll

discuss why we want to set up the tours

in the following video so let's start

over here we're going to go with if and

then is loading okay good and then we're

going to go with heading three loading

and then d da D okay good then we also

want to do the same thing pretty much

for

error so now we're checking for this

value and we're going to go with error

and actually we can display the message

as well just in case there is any so I'm

going to go with error and let's access

the error

message is error and then I'll just

leave this one for now So eventually

we'll iterate over that doors so now let

me navigate to the browser again if

everything is correct we should see

those doors and I can see the array of

Five Doors so that works should also

have that loading for a split second and

let's say if we're going to mess with

the URL if I'm going

to provide the wrong URL notice now I

have actually error failed to fetch T

and now again let's reiterate why do we

need a type so let's try to set up do

state value at the moment we don't have

the type so essentially we'll just

provide Mt then let's try to set it over

here in the fetch data and then let's

iterate over and see where the issue is

going to be so for STS we want to go

over here with const tours set tours

okay beautiful then we want to go with

use State and remember if we're just

going to provide over here Mt aray which

will be default value notice now T is

actually set equal to never which means

that yeah I can go over here and I can

go with set tours I can provide broad a

okay beautiful everything is awesome and

then let's say right after the react

typescript we're going to go with doors

then map so we're iterating over and

then as far as the function well let's

access the tour correct okay good and

then we're going to go with some kind of

heading two we provide hello we can even

see those hellos in the browser okay

beautiful but what if we're going to try

something like this let's say I want to

access one of the properties I'm going

to go with the name one so now if we go

here and say tour and that name this is

not going going to fly typescript is

going to say well you cannot access the

name property on type never and this is

why we do again need to set up D type

and in our case since we already know

how to work with Zod and since we're

going to use Zod

to evaluate our data at run time anyway

this is going to be our approach okay so

now let's set up our type and we'll do

that with the help of Zod Library since

that way we can also check the data at

runtime and this is totally up to you

you can set up the file name utls or

something along those lines I think in

my case I'm just going to go with types

now as a side note also in this file we

will set up a fetch

function with the axio so that is coming

up so basically we'll just Jam bunch of

the things normally in the bigger

project you would separate them but I

don't think there is any need so we're

looking for Zod Library which again is

already installed if you're using the

star if not then just please install the

library then let's construct that door

schema which will also then infer to be

our door so let's export that since we

also want to use that one in the inex so

we'll go with export then con store and

then we're looking for schema over here

so this one will be equal to Z do object

so this is what we're

constructing and I believe I had five

properties in there so all of them were

string that's for sure so we're going to

go over here then let's copy and paste

and I believe it's one too many by the

way so let me remove this one and then

we have one for name also we want to set

up over here image then same deal info

and at the very end we'll have the price

one I'm missing comma

so let me do that as well and now let's

construct our type this is something

also we're going to export so let's go

here with export type and then tour and

that is equal to Z infer so now we just

infer a type which is a generic and

we're just going to go type off and then

to our schema so now we have both we

have our schema and we also have our

type so now let's navigate back over

here and we want to import both of those

things we want to grab the tour as well

as the tour

schema so let me set her up I think I'm

going to type over here type tour just

to make it more explicit what we're

doing so we want to grab the scheme as

well and then this one is coming from

the types let's save this and now let's

just start using the type and I guess

right away also the tour schema so here

where I have the hug state for tours I

actually want to go with tour and the

array so essentially I'm telling

typescript that yeah this is an array

but eventually it will be an array off

TOS then we're going to keep on moving

and where we have the raw data same deal

I'm going to go a tour and I'll set it

as an array then we actually want to run

right now our tour schema remember there

is an array method and again I want to

save pars it so essentially I want to

throw the a myself and it's going to be

nicely caught over here so for now I

think I can remove both of these ones

over here we won't use them and

essentially we want to get that result

so let's go to the result then T schema

array let's invoke this and then we're

going to go save bars and and we're

looking for raw data and then as far as

the result remember we're checking for

the success

property and essentially if the data is

not present then we're just going to

throw the error so we're going to go if

and

result

success that's not the case then I mean

you know what I can actually log it so

let's go the

result error and message over here and

also we want to throw our own error so

let's go throw new error and again let's

do the same thing we'll go with failed

to

parse and tours and then at the very

very end we want to go here with set

tours and we want to pass in result.

data so if we're successful if we bypass

this condition pretty much we're good to

go and I think at this point essentially

we can just navigate to to our return

and we can just set up the proper return

so in here let's go with the heading two

I'm going to add some class so I'm going

to go with margin bottom and set it

equal to one then we're going to go here

with doors okay and then let's iterate

over so we have tours over here we want

to call the map and now once I type the

tour it will nicely be my object

everything starting with ID all the way

to a price and again this is something

that doesn't stop to amaze me so we're

going to go over here with return then

we want to set up the paragraph again

we're not going to really work on

Amazing result in the browser for now we

just want to grab the T ID we want to

add some classes over here so class name

and let's go with another margin bottom

one and then let's access the door Dot

and we're looking for the name and again

if everything is correct this is what we

should see in the browser yep everything

is awesome and if we go over here to the

types and let's say I'm going to add a

property I'm going to say that I'm

looking for something and that will be a

string and let's invoke that check it

out first I have over here a error

message in the console and we can also

see that over here now million doll

question do you always need to add Zod

when you're fetching data and to tell

honestly most likely that's not

something that you're going to see that

often for the most part you're just

going to rely on the fact that yeah the

API is supposed to return some kind of

type but it does come in handy when you

definitely definitely want to check for

that particular value so this is how we

can essentially Fetch with react and

typescript with the good old use effect

and fetch API and now let's see how we

can accomplish the same thing with less

lines of code and essentially no

headache and we're going to do that with

the help of axios and react query and if

you're not familiar with either of these

libraries please utilize the library

docs or some other online resource since

our main focus is going to be on

typescript and I actually want to start

by constructing fetch tours with

axios again normally you would set this

up in a separate file but in this case

I'm just going to do it right here in

the types where I want to install or you

know what actually it's already

available in the starter we simply want

to import the axios from axio library

which is an awesome HTTP library and

effectively we want to construct right

now the fetch doors and you know what I

also so I'm going to grab right away

this URL and I'll actually remove it

from the file since we'll set up use

Query over here as a side note as always

you can find

the code from previous lessons in the

read me so let me go over here this is

going to be my URL and essentially we

want to go with export const fetch doors

it will be a sync and as far as what

we're returning since it's a sync

function we want to go with promise and

then we'll set up our tour array and

then when it comes to functionality we

want to use axos and we want to stick a

weight in front of it so let's go with

const

response and that is equal to a

wait then axos doget remember this is

actually a generic and therefore in here

we pass in door and array so an array of

doors and effectively in this response

inside of the data property we'll get

back our array but it will be nicely

already set as type array off doors

hopefully that is clear and we actually

did cover that during the tutorial part

now let me double check over here it

looks like I have a syntax bug yep now

everything's correct so we have response

beautiful

then we'll do the same thing like in the

previous video where essentially I just

want to check using Zod and since it's

pretty much the same code let me again

just take it out and set it up over here

so we still use the result to or schema

in this case we're not passing a raw

data we actually go with response. data

again that's where the array is going to

be located and then from this function

we want to return

and we're looking for result. data so

since we have multiple libraries yes

we're pretty much passing this array

from one to another so first we use

axios and again just to demonstrate that

basically if we go over here with type

definition you'll notice somewhere here

get see over here it's a generic and

essentially it has this axio response

and then if you take a look at the xos

response one

notice this data it's a generic type

correct so whatever we pass in this is

what we're going to get back and once we

have this function in place now let's

navigate I guess actually to the main

DSX because we want to wrap everything

in the query client provider so we want

to install react query Library you can

also install Dev tools they have as some

Dev tools but in this case we're not

going to do that and in here we want

import the query client as well as query

client provider first we want to set up

a new

instance like

so and as a sign not something I want to

mention react query is actually very

good at inferring the types so as far as

types is concerned we actually don't

need to do much as long as we set up a

proper return type here in the function

basically what we are returning pretty

much we're good to go

so in here we want to go with new query

client let's invoke this and then we

want to wrap our app inside of the

render so let me set up my query client

provider we're looking for client that's

the prop and we'll set it equal to a

query client then let's wrap the app and

now let's navigate to index DSX and like

I said I'll pretty much start everything

from scratch and if you want

the code from the previous lesson please

just utilize the read me in here we're

looking for fetch dos a function we just

set up it's actually located in the

types okay and we also want to grab this

hook which we get from react query

called EU query again this is coming

from and in this case we have this stand

stack and react query so we have both of

these Imports now let's set up our our

component and let's also set up the

export since I know that I'm going to

forget to do that let's export the

component as default and for starters

let's invoke use Query so we're going to

get bunch of the things back and we want

to set it equal to use Query so notice

we don't need to set up our loading

error or any of that stuff and I'm not

even talking about the use effect

essentially we just invoke the use Query

and and we're good to go it's looking

for two things it's looking for a query

key since we'll nicely be able to

invalidate those queries later something

we're not going to do but just telling

you it is an option so essentially you

just provide some kind of string over

here so now this

query we will reference with the name of

doors just in case we ever want to do

something with the query like for

example invalidate and also we want to

set up a query function now this query

function has one rule and one rule only

it needs to return a promise that's it

that's all we need to do now if we

navigate to types what is this function

doing it's a sync what does that return

it returns a promise and like I said

react quer is awesome at inferring the

type so if we set up properly over here

that I'm going to be returning an array

of Tours react query is going to figure

that out so in here since I'm not not

passing anything in Fetch dos any kind

of argument I simply can set up the

reference now what are we getting back

over here we get back is pending so this

is while we're loading we get back is

error if there is any we also get the

actual error object just in case we want

to get the message and just like axios

in here we have this data one and inside

of that data we'll have that array of

Tours now since I want to use pretty

much the same name I'm just going to

give it an alas of Tours okay good and

with this in place now let's set up our

return so one by one uh first we're

going to go with is spending so check

that one if that's the case again same

deal we're going to go with heading two

or heading three and we'll go with

loading then we're going to go with is

error so if we have the error actually I

do want to

access the error message so let's go

here with error and we'll set it equal

to error object and in there we have a

message property and now let's iterate

over the tours and same deal essentially

we just want to showcase the tour name

in some kind of paragraph so let me set

up the return we're looking for div

inside of the div we're going to go with

heading two let's add a class name

margin bottom set it equal to one that

will be equal to

tours and then we want to iterate over

so let's call

map then each and every tour okay good

and then we want to return from the

function and I'm going to go with my

paragraph let's add a class name of

margin bottom one and also let's add a

key and we'll set it equal to tour and

then ID and then inside of it let's

render the door. name and if everything

is correct again the result is going to

be the same but like I said way less

headache way less State

values and pretty much everything is

already inferred so we only need to set

up a use Query we only need to set up

fetch doors and pretty much we're good

to go okay and now let's cover Redux

toolkit setup which is a good option if

you have a global State as side note if

you're not a fan of Redux

toit a Nifty alternative is Library

called zustand I believe that's how it's

pronounced which offers pretty much the

same functionality but with less

overhand and the code is also less

clunky I have to admit but since at

least at this point in time you will

encounter Redux to K it more often I

settled on rtk as far as typescript

Redux toolkit just like react query also

nicely infers bunch of the things so

it's actually less work than for example

use reducer but I'm not going to lie the

setup so the initial setup to add Redux

toolkit to our application with

typescript is somewhat of a pain now the

good news it's a boilerplate setup so we

can take it from Project to project so

most likely you'll only need to write it

once and in fact we will do a setup in

the following video so for now we'll

just prepare everything we'll actually

create our first slice and then in the

following video we'll complete the

boiler plate setup for Nots we want to

go to app DSX we're looking for starter

rtk the component if everything is

correct this is what we should see on

the screen and since we're shooting for

the same functionality as in use reducer

I suggest navigating to read me and just

grab this code so again this is just

going to set up some buttons

which we will use later to control our

state values so grab

everything in here as far as the

component is concerned you want to

navigate back over

here paste it and again you should have

five buttons and pretty much every time

you click on a button there's going to

be some kind of console log and then we

want to set up a slice now slice in

Redux tokit essentially is just a piece

of functionality so let's say in your

application you're handling the user so

the log out login whatever all kinds of

things well you'll set that one up in a

slice let's say you have a theme you'll

create a slice for that and hopefully

you see where I'm going with this now in

our case we'll just dump everything in

one so I'll say cter slice and we're

looking for TS since we're not creating

a react component then we want to import

two things so create slice is going to

create that slice for us it's a function

coming from Redux toolkit and second one

will be payload action which actually is

a type and this is something we're going

to use towards the end of the video so

now let's go with create and Slash

okay that's what we want to import over

here good then let's also grab that

payload but this is actually a type so

payload action and yep it's coming from

Redux toket beautiful now we will set up

some types in a second let's start by

creating that

slice so counter

slice and this will be equal to create

slice and second will provide some

values before I forget I do right away

want to export and actually we export

the reducer function so we go here with

default counter slice and then dot

reducer so this is something we're going

to use when we set up the store so think

of store as pretty much your entire

State and then the slice well this will

be that one functionality again in our

case pretty much that will be the only

functionality but in bigger applications

this is where you'll set this one thing

and as far as the crate slice it's

looking for a few things it needs to

have the initial State and we'll also

right away set up those reducers so you

know what let's just start setting

everything up if you remember when it

comes to the state we have count and

Status over there and then it will be

our initial State and this is something

that we're going to provide over here

here in the create slice so let's start

here const

initial state for now I'm not going to

set the type I'm just going to say that

count is equal to zero and then status

will be pending and remember we'll just

control it from active to inactive I

believe then inside of the create slice

we want to come up with the name and

essentially I'm going to call this

counter and then also we want to go with

our initial state in a second we'll set

up the reducers which control it but

before we do that well why don't we just

knock out those types over here so first

let's set up a type for the counter

state so type counter and state and in

here count will be equal to a number and

then when it comes to status I'll

actually set up the literal type because

we'll use it later to provide a proper

type to payload action so we might as

well set it up separately so let's set

up a status but instead of setting up as

a string I'll actually create another

type I'll call this counter status so

this is essentially something we control

when we add that payload over here now

when it comes to a counter we'll press

these buttons over here without the

payload and as far as the literal values

well we're going to go over here with

active

inactive and let's also add the bending

one and once I have this one in place

status actually is going to be equal to

a counter status so now where I have the

initial state I'm going to go with my

counter State and then we want to set up

those reducers so reducers are going to

be functions which essentially control D

State and then in order to invoke those

functions we'll need to display patch

them and again remember when it comes to

actual count the number the only thing

we need is whether we want to increase

decrease or reset but when it comes to

set status this is where we actually

pass in the payload now the good news

with Redux toit effectively if we're

just controlling this one value we don't

even need to provide D type and you'll

see what I'm talking about in a second

so we want to go with reducers it's an

object and then one by one let's up and

pretty much I just come up with a

function name so for example in this

case increment I right away have access

to a state and as side not yes redex to

it nicely inverse all of the values that

we need over here and then yes we can

essentially just overwrite so I can just

go with count plus and equals to one so

notice I don't need to provide my type

since I'm not providing any payload

that's it I only want to set up this

function over here and we will export it

in a second and eventually we will

dispatch it hopefully that is clear then

we want to go with uh decrement I

guess let's go with State same

deal we want to go with State count and

in this case we'll subtract and then

when it comes to

reset we just want to access the state

okay good and then set the state count

equals to zero as then note if you're

wondering why we can just modify the

state like that why don't we need to

return state from this function it's

because under the hood essentially Redux

is using a library which does that for

us so that's why we can actually kind of

modify the state directly in here under

the hood yeah we're still getting the

latest value don't worry and then we

have the St status which essentially is

going to have two things not

only we'll need access to a state but

this is the case where we will provide

eay load so effectively when we dispatch

set status we will provide that string

value and the string value is actually

one of these ones so either active

inactive or it's going to be pending and

when we use a Redux stol kit we do have

this special type which we need to use

so it's called payload and for some

reason not using so payload action not

sure why I'm not able to access that so

payload

action and it is a generic over

here and then inside of the generic we

want to pass in our own type so

basically we need to provide over here

this counter State now I do have over

here a syntax error and now as you can

see everything works so if you have the

action yes you'll need to provide this

payload action which again is a generic

and then in here you'll provide the type

so in this case it's somewhat

straightforward we just have a string

but keep in mind yes if you have let's

say an object with a bunch of properties

you'll have to set up the type and

provide it over here so typescript knows

what do you want to do essentially when

you pass in that payload and same deal

we want to go with state. status and

that will be equal to action payload

since that's where we have the string

now it looks like I have a bug my

apologies by mistake I provided the

counter state it should be

counter status my apologies now

everything's correct I don't have any

bugs and also we want to export the

increment decrement all the way to set

status so we won't need to provide in

our component let's say a type when we

dispatch we simply can pass in our

action and we'll be good to go so we go

here with export const and then we

should have access to all of our

functions so increment decrement reset

and then set status and that one will be

equal to counter slice and then we're

looking for actions this should do it

for the slice setup and in the following

video we'll do that somewhat annoying

boiler plate setup where we'll add the

Redux tokit to our application okay and

now let's take a look at that

boilerplate setup where effectively we

want to create two files we want to

create store DS as well as the Haw DS

and as a side not if you're using the

starter you should have already those

files now there shouldn't be any code in

them but you should have the files and

store is where we set up all our slices

so we create that Global store and hooks

is a special one because we're using

typescript and you'll see what we need

to do over there in a second so first

let's start with the store we want to

import configure store this is coming

from Redux tokit and also we want to

grab counter

reducer now this one is coming from our

slice the counter slice and I need to

make sure that it's coming from the

start so let me go over here with the

reducer from and let me look for

star then the rtk and then I want to get

the counter slice let me just double

check yep I'm exporting so everything is

correct and then back in a store we want

to invoke configure store so we want to

go here with export con store since

we'll wrap our entire application in the

store and inside of this function we

have a reducer property and essentially

this is where we set up our slices so in

our case again we have only one so I'm

going to go with counter is equal to

counter reducer since we're using

typescript we need to set up two more

types so export type and again in the

docs they use this root State they set

it equal to return type and inside of

this one they go type off and then store

and get state so this is what they pass

into this generic and the second type

when you want to set up over here is

export type app and dis

patch and this one will be equal to type

off and store this patch so once we have

these two types in place we want to

navigate to The Hook one and essentially

we want to grab use dispatch and use

selector so those are the two hooks we

use with Redux toit one is to access the

store and second one is to dispatch an

action

and we want to create our own and you'll

see what that entails in a second so

let's first grab use this patch again

this is coming from react Redux so this

is what I was talking about the annoying

boiler plate setup but again you only

need to realistically do it once so then

import this is actually a type and we're

looking for typed

use selector hook so this is coming from

react Redux and also we want to grab

that root State and app dispatch the

types we just set up so let's go here

with root and state somewhere yep that's

the one and I also want to grab the

dispatch okay we have both of these so

now let's set up both of those hooks so

we're looking for export const

use and the name is totally up to you

just make sure that it starts with use

that's just a rule for react talks and

in this case we'll actually go with the

function and we're going to go with app

dispatch and we'll set it equal to use

dispatch so it's going to suggest this

use app dispatch that's not what you

want to use you want to go with use

dispatch which is actually the second

one and then let's also set up the use

app selector which also we're going to

export so we go here with use

app selector and in this case we just go

with type selector hook we provide the

root

state or type that we have in a store

and we'll set it equal to use selector

here let's save it and now the last step

is going to be in the main DSX where we

want to import the entire

store from store file and and we want to

wrap it in the provider component which

is coming from react Redux library now

this provider component is looking for

store prop and as far as the value we'll

pass in our store so let's go here with

provider then

store set it equal to our

store then let's wrap it and with this

in place we have successfully added redu

toit to our application and in following

video we'll complete the functionality

okay so now let's navigate to 09 rtk

index DSX and we want to import few

things first we'll grab those hooks so

instead of use dispatch and use selector

we're going to go with use app selector

use app selector and we also want to

grab use app dispatch and then also

let's grab those actions from our slice

so I'm talking about decrement increment

reset and set status so let's grab also

this one this is coming from the counter

slice good then we have increment then

we have

reset and then we also have set status

all of that is coming from the counter

slice now in order to access the state

values we want to go with the use app

selector so that's the hook and

essentially by default it right away has

access to the entire state so I'm

talking about this one over here more

specifically we're looking for the

counter so we're going to go over here

and we're going to say State and as I

not I do need to pass here function and

then from the state we want to access

the counter so this will be our tiny

slice for the counter and we can nicely

right away the structure two things what

do we have in a state we have the count

as as well as the status so those are

the two things that I want to access so

now where I have the count I'll actually

change it around and I'll set it equal

to count and as far as the

status same deal over here now just to

keep it more interesting I'll actually

navigate back to my counter slice and

let's say set up my initial value to be

equal to 15 so now I can clearly see

that I have access to the counter as

well as my status one so now we just

want to navigate back and we also want

to invoke the use app dispatch which is

going to return a dispatch function we

can invoke so let's go here with cons

dispatch set it equal to use app

dispatch and then where we increment

decrement and reset we'll just invoke

these functions and then when it comes

to set status remember we also need to

pass in the payload so it's going to be

a little bit more code so we want to go

here with this patch and we just want to

invoke the increment same deal is going

to be for decrement and

reset so I'm pretty sure I can just copy

and paste so we're looking for decrement

over here and then lastly we have one

for reset as well so let me override

this one that should do it notice now

we're actually changing the count value

and when it comes to set

status it's pretty much the same we just

want to actually pass in the string

value whether that's active inactive or

pending so let's go here with dispatch

set status and again we'll get a nice

suggestion so these are the values that

we can pass in so it's kind of hard to

mess up so let me copy this set it up

over here and instead of active we're

going to pass in inactive so now let me

navigate quickly to browser and it looks

like everything is working as expected

and with this in place we have

successfully added Redux toolkit to our

application all right and up next let's

build a small tasks application before

we start coding away let me just mention

that if you enjoy the challenge and want

to build this project independently in

the readme you will find a list of steps

to build such app so if this is

something you're interested in pause the

video complete the steps independently

and resume once you're ready to compare

the results as far as the app it's

actually very similar to the app we

already built at the end of the

fundamental

section essentially we will create a

form and a list of tasks and if the user

provides a valid input we'll add a task

to the list and with the help of the

checkbox user will be able to toggle

whether the task is completed or not now

we'll start just like the other examples

where we want to navigate to app DSX and

we want to grab our components so in

this case we're looking

for folder number 10 I believe right so

we're looking

for

starter then forward slash and

tasks so let me replace whatever I have

in

here let me set up the component yep I

have task list so that is good and just

like before since we're working with

typescript one of the first things we'll

do is to set up a type and since we'll

use this type in multiple files it

definitely makes sense to set up types

yes and in this case there's going to be

only one type which will be a task so we

want to go with export type task and in

here we have three properties ID which

will be actually a string then a

description which will also be a string

and then is completed which will be a

Boolean let's set it up and then we want

to create two more components which will

render in the index DSX so so we have a

form component we set it up and also

there's going to be a list one new file

and we're looking for a list and then we

want to create our component and with

this in place now we want to navigate

back to index and we want to import use

effect use State as well as form and

list and also the type so one by one

let's set it up so use State then let's

also grab use effect and then let's grab

the form

one list

one and at the very end let's also grab

that type so import explicitly I'm going

to type task and then this is coming

from the types now inside of this

component essentially we want to start

by setting up the state value so in here

let's go with tasks set t tasks and this

one will be equal to use State let's

invoke this one and by default it's

going to be an empty array but we do

want to provide the generic over here

and we'll say that it's going to be an

array of tasks and when it comes to our

return I think I'm going to replace the

div with a section and in here let's

type the form component first and we

also want to display the list let's save

it over here now for some reason I don't

see anything looks like there's a bug so

it complains that Forum doesn't provide

the

import this is strange oh yeah probably

because I didn't save it my bad let me

try one more time if everything is

correct this is what we should see in a

browser and with this impl now we can

start working on the form functionality

okay and when it comes to form

essentially we want to set up the form

element inside of it there's going to be

an input and it's going to be a

controlled input so there will be a

state value as well and once we submit

the form we want to prevent the default

we want to check whether there is a

value provided in the input if not then

we will trigger the alert and if

everything is correct We'll add task to

the list something that's coming up and

also we'll set text back to empty value

I guess I'm going to start by setting up

two Imports over here so we're looking

for use State and also we want to grab

that type because eventually we will use

it not for now but let's go with type

and task which is coming from our types

and then let's start I guess by setting

up that state value so we have text and

set text and that one is equal to use

State and we want to start with empty

string eventually we'll set up the

handle submit for now I just want to

work on the return so we're going to

return a form element We'll add some

classes just so it looks a bit more

representable and we're going to go with

task form so again on submit is coming

up let's not worry about it right now

inside of the form we want to go with

input type will be equal to a text class

name is going to be form input

and also we want to set up the value

since this will be a controlled input

and let's also set up the

onchange I'm going to provide the inline

function since I don't want to bother

with the event type and we're just going

to go with set text and we'll go with

event. Target and value okay good and

then we also want to set up the submit

button so button then type is equal to

submit and class name will be equal to a

button and we're going to go with add

task let's save it this is what we

should see in the browser so now let's

just navigate back and set up that and

I'll submit so first let me I guess set

up the function this is going to be

essentially a repetition pretty much for

stuff that we already covered during

tutorial so we're going to go here with

handle submit remember we do want to

access the event but we do need to

provide the type ourselves in this case

so we're going to go with form event and

we're looking for HTML and form element

this is what we want to pass in and as

far as the

functionality first we're going to

prevent a

default so prevent default let's invoke

that then we'll check for text so if no

text provided then we'll go with alert

and let's just go with please enter a

task then we're going to return so we're

not going to do anything and if

everything is correct basically if we

bypass this condition then we're going

to go with that task and we'll go with

set text and we'll set it equal to an

empty string so now let's just look for

the form we're looking for

onsubmit and we'll set it equal to andle

submit so let's see let's see let's see

I think we can just log so instead of

adding the task for now let's just see

what is the text value whether we are

successful let me type some nonsense

here and looks like everything's correct

so I get the value in the console and I

also end up with an empty input now if

I'll try to submit without providing any

value then we'll get back the alert and

with this in place now we can start

working on the add task functionality

all right and up next let's set up

functionality to add task to the list

now we can take multiple approaches

essentially we can pass down set tasks

to a form and let's say if the value is

provided we can invoke set tasks it's

definitely an option but in my case it's

just a preference to set up everything

in the parent component and therefore I

will create another function and I'll

call this add task now this function is

looking for one thing and one thing only

which is a task but remember we have a

specific type for that so we want to go

over here with the task now it doesn't

return anything so we can just call here

void and as far as the functionality

inside of the function body we just want

to go with set tasks we want to spread

out all the existing tasks and then we

want to add the new one so we'll go over

here with tasks comma and then we will

add the task which was Prov divided to

add task we do want to pass this down so

add task is equal to add task and if

everything is correct we should get

bunch of red squiggly lines somewhere in

this case it's in the index DSX simply

because we haven't set up form to accept

any props so let's work on that we

already have D type task so now let's

set up our type here for the props I'm

going to call this for props and in here

I'm looking for add task function same

deal it's looking for this argument the

task one and it's actually type task and

then when it comes to the return we're

just going to go with void and then

right after our condition I think I can

remove that console log I don't think

there's a point anymore we can just go

with add task and essentially one by one

let's provide those properties we have

over here remember it has to be a string

so I'm just going to go with date then

I'm going to invoke get time method

and eventually I'm just going to turn

this into a string then I still have red

squiggly line

because I mean I actually haven't set up

the props properly my bad what am I

doing let me go here with add task and

this is actually going to be equal to a

form props

and now we get the correct red squiggly

lines where essentially we can see that

few properties are missing so let's

provide them we're going to go with

description so this one will be equal to

a text and also let's go with is

completed which we will hardcode and set

it equal to false now I don't have any

red squiggly lines and once we navigate

to the browser I'm actually going to

open up the components just so I can

see what we have as far as the state and

now let me go with first task me invoke

this and yep notice over here we are

successfully adding this task to our

list all right so we're pretty much done

with the form I don't think we're going

to work in that component anymore now we

just want to render the list and also

toggle the task remember it has that is

completed property which is Boolean um

and just like in the fundamentals

project we just want to display some

checkbox and then every time we will

click on that checkbox then we'll toggle

that value and actually before we

render the list I do want to right away

set up this function since we'll pass it

down to a list

component the functionality is super

straightforward where we want to go

toggle task now this function is looking

for the ID so so therefore let's right

away set up the inline type annotation

and let's say that ID is actually going

to be type string now as far as the

actual functionality we want to go with

set tasks and then remember when we

invoke map we get back a new array so

now I just want to iterate over the

array and if the ID matches the task ID

I want to set the task is completed to

the opposite value now if it's not the

case if they don't match then we just

return task as it is so let's go with

tasks map and yes as a sign not there

are Million Ways How we can write this

functionality I just went with this

approach so we're going to go here with

task then we'll check if task ID is

equal to ID we're passing in then we

want to

return this task with a new is completed

value so we want to spread out the

existing task and we want to go is

completed and set it equal to the

opposite so we're going to look for task

and then is completed now if it's not

the case then we'll simply return the

task and with this in place now we can

pass this toggle task down as well as

our entire tasks list so first prop will

be tasks and the second one actually is

going to be toggle task now we haven't

set up of course anything in the list so

all of that is coming up let me just

pass this down we're looking for toggle

task then let's navigate to our list and

first let's grab our task we will need

our type so import type task and that is

coming from my types yep that's the one

and let's set up right away the list

props so type list props and in here we

have tasks which is actually an array of

tasks and also we want to set up that

toggle task so toggle task same

deal it's going to have the ID and

actually that ID will be a string but

notice how essentially we're providing

an object correct so make sure you have

the same syntax okay good and in here we

want to the structure both of them so

tasks and toggle task and we'll set it

equal to list props beautiful and now we

want to iterate over the list display

all the items and also let's right away

set up the toggle task functionality so

we're going to go over here with Anor

list let's add a class name of list then

inside of the unor list let's go with

tasks. map let's invoke this and over

here we're going to have a task and then

for every task we want to set up the

return it's going to be a list item and

also we'll provide a key that's a must

so we're going to go here with task

ID Also let's set up the paragraph This

is where we'll display the task

description as far as the classes we're

looking for task and text and over here

let's set up task and description so we

have access to that and now let's set up

our input so at the very end over here

we're going to go with input now it's

not going to be a text actually we'll go

with checkbox we're going to go with

checked so it has this prop and we're

going to set it equal to task and then

dot is completed so if it's true then

the checkbox is going to be checked if

not then it's not going to be the case

and we'll right away add this onchange I

will pass over here the inline function

we don't need actually the event I

simply want to go with title task and

then I want to provide the object with

the ID property where I'm looking for

TAS ID now before you ask can you

essentially set up this

ID as a straight up argument so

essentially without that object yes

absolutely it's just my preference to

set it up as an object in this case and

with this in place we're done with the

list as well as toggle task

functionality so if I add a second one I

can nicely toggle over here this value

as well now if I'm going to refresh the

page of course I'm going to lose all of

the values since we haven't set up the

local storage yet and in fact this is

something we're going to do in the

following video okay so now let's just

add local storage to our application and

I want to start by navigating to the

browser to the application and I want to

remove the previous ones I believe I

still have values from the fundamental

section then we want to create two

functions one is going to be load tasks

so we want to load the tasks when the

application starts up and we'll also

have one to update the storage and since

it's a react project we can use use

effect and then pretty much every time

there's going to be some change in a

tasks list we will invoke the update

storage let's start with the

load tasks function so this function is

going to return an array of tasks as far

as the functionality we want to go with

stored tasks so that is equal to local

storage then we're looking for get item

that tasks something we don't have yet

and then we want to

return and then based on what we have in

the local storage either we're going to

return those tasks or we're going to

return an empty array so let's set up

turning operator we're going to go with

Json parse and we'll pass in stored

tasks that's not the case we'll return

empty array and then in here I'm just

going to provide a function and then I'm

going to invoke load tasks and then like

I said we also want to set up one to

update storage so every time we'll

change something about the list be it

add the task to the list or toggle D is

completed we'll update the storage so

update storage now this one is looking

for the tasks and actually it's going to

be an array of task now it's not going

to return anything so we're just going

to go with void and then we want to go

with local

storage then dot we're looking for set

item the name is going to be tasks and

we're going to go Json stringify since

we can only store strings over there and

we'll provide the tasks so this is how

we're going to create those items and

then when the project

loads this is how we're going to access

them like I mentioned since this is a

react project

we can go with use effect and then

pretty much every time there's going to

be some change in our dependency array

which contains the tasks we will also

invoke the update storage and we'll grab

the tasks value so now let me navigate

back to the browser or it's over here

everything is empty I have no tasks but

I can go with first task okay good

second task task notice how they are

actually saved in local storage I can

also toggle the is completed and then

once I refresh I still preserve the

values that should do it for typescript

with react section hopefully everyone

enjoyed it and up next we're going to

start working on a big typescript

project where we're going to implement

most of the things that we have learned

in fundamentals and react with

typescript sections