Original subtitles

One thing that separates JavaScript

from a lot of programming languages, is that JavaScript is a dynamic

language. What do I mean by dynamic? Well,

we have two types of programming languages. Static languages or

dynamic languages. In static languages, when we declare a

variable, the type of the variable is set and it cannot be changed

in the future. In a dynamic language like JavaScript,

the type of a variable can change at run time. Let's see this

in code. So back in the example from the last lecture we have declared

this name variable, and we have set that to a string, so

the type of name is currently a string, but it can change in the future.

Let's take a look. So here in the console, we can execute some JavaScript

code, we have this type of operator,

and with that we can check the type of a variable. So after that

we add the name of the variable. In this case the name variable

So note that the type of name is a string. So,

if you reassign name to a different value, like a number,

and check it's type,

look, the type is now changed to a number, this is what we call

a dynamic language, so unlike static languages the type of

these variables will be determined at runtime based on the values

that we assigned to them. Now, let's take a look at a few more examples of the type

of operator. And by the way, note that type of is

another reserved keyword, so we cannot have a variable called

type of. So, we can clear the console by

pressing control and L. So now let's take a look at

the type of age, it's a number. Now if we change

age to a floating point number, and I know it doesn't make sense, but

let's just stick to this for example, 30.1,

and then look at type of age, it's still a

number. So in JavaScript, unlike other programming languages

we don't have two kinds of numbers, we don't have floating point numbers

and integers, all numbers are of type number.

Now, let's look at the type of is approved, it's a

boolean as I told you before, what about the first name, let's have a

look. Type of, first name. It's undefined.

And that's funny, because the value of this variable is undefined

but it's type is also undefined. What does this mean?

Well, earlier I told you that we had two categories of types,

we have primitives or value types, and reference types.

In the primitive types category, we have strings, numbers,

booleans undefined and null. So undefined

is actually a type, but it's also a value.

In this example, because we have set first name,

to undefined as a value it's type is also

undefined, okay? But what about selected color.

Let's have a look, so type of selected color.

The type of this variable is an object.

What is an object? That's a topic for the next lecture.