Datatypes and Variables

Primitive Data types

String
Number {int , float}
Boolean

CHECK BELOW TO KNOW ALL THE DATA TYPES 👇

String

A string is a data type used to represent textual data. It consists of a sequence of characters enclosed within single ('') or double ("") quotation marks.

Example :

"Hello, I'm a string"

'Hello, How are you...'

Number

It Represents numeric values, both integer and floating-point numbers.

int float

a. Int

Integer numbers are whole numbers without decimal points.

Example :

123456

b. Float

Floats are numbers with decimal points.

8793.90

Boolean

A boolean represents Logical values Like : true or false( one of two possible values).

true or false

What is Javascript Engine?

A JavaScript engine is responsible for executing JavaScript code in a web browser. Browsers utilize engines like V8 (used in Chromium-based browsers), which compiles JavaScript code and produces the desired output.

Variables In Javascript

A variable is used to store data. There are three keywords to declare variables:

let, const, var

Syntax :

keyword variableName;

Example

let age;

In The above example we can use let keyword and declare one variable name of that variable is age. This is declaration part of in the variable.

age = 20;

In The above example we assign 20 value for age variable. This 20 value is stored in age variable. This is assignment part of in the variable.

Example

let age = 20;

In the above example we create declaration and assignment part at same time.

let

Let keyword used to declare variables in JavaScript. Variables defined using let Cannot be re-declared within the same scope.

Code

<!DOCTYPE html>
<html>
  <head> </head>
  <body>
    <script>
      let age = 20;
      console.log(age);
    </script>
  </body>
</html>

Output

20

In the above example we can create one variable using let keyword name of that variable age. we store 20 value in age variable. In next line we print value of console.log(age);age variable.

Code

<!DOCTYPE html>
<html>
  <head> </head>
  <body>
    <script>
      let age = 20;
      console.log(age);
      age = 50;
      console.log(age);
    </script>
  </body>
</html>

Output

20
50

In the above example we can create one variable using let keyword name of that variable age. we store 20 value in age variable. In next line we store 50 value in same variable. In next line we print value of console.log(age); age variable. But the output of above eaxmple is 50 because one variable store only one value at a time.

Code

<!DOCTYPE html>
<html>
  <head> </head>
  <body>
    <script>
      let age = 20;
      let name = "Suraj";
      console.log("Name:", name);
      console.log("Age:", age);
    </script>
  </body>
</html>

Output

Name: Suraj
Age: 20

Example

<!DOCTYPE html>
<html>
  <head> </head>
  <body>
    <script>
      let age;
      console.log(age);
    </script>
  </body>
</html>

Output

undefined

const

const declares a constant variable that cannot be reassigned.

Example

<!DOCTYPE html>
<html>
  <head> </head>
  <body>
    <script>
      const age = 20;
      console.log(age);
    </script>
  </body>
</html>

Output

20

var

var is an older way to declare variables with functional scope.

Example

<!DOCTYPE html>
<html>
  <head> </head>
  <body>
    <script>
      var age = 20;
      var age = 30;
      console.log(age);
    </script>
  </body>
</html>

Output

30

Difference between var, let and const

	var	let	const
Scope	The scope of the var variable is the functional scope.	Let allow us to declare a variable that is limited to the scope of a block.	The scope of the const variable is block scope.
Updates	It can be updated and re-declared in scope.	It Can be updated, but not re-declared within its scope.	Cannot be updated or re-declared after being defined.
Initialization	Can be declared without being assigned a value.	Can be declared without being assigned a value.	Must be assigned a value when declared.
Access	It can be accessed without initialization because its default value is undefined.	It cannot accessed without initialization, or a "reference error" will be raised.	It cannot be accessed without initialization because it cannot be declared without initialization.

Rules to declare variables:

Use letters a-z, A-Z, digits 0-9, and underscore _.
Variables cannot start with numbers.
Variable names cannot be reserved keywords.
Variable names are case-sensitive, which means name and Name are considered different variables.

Primitive Data types​

What is Javascript Engine?​

Variables In Javascript​

let​

const​

var​

Difference between var, let and const​

Rules to declare variables:​

Primitive Data types

What is Javascript Engine?

Variables In Javascript

let

const

var

Difference between var, let and const

Rules to declare variables: