JavaScript Variables – GeeksforGeeks

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Variables are the constructing blocks of any programming language. In JavaScript, a variable can be utilized to retailer reusable values. These values will be something from Quantity, Boolean, String, and even a price returned from a operate. The values of the variables are allotted utilizing the task operator(“=”). 

There are some primary guidelines to declare a variable in JavaScript:

  • These are case-sensitive
  • Can solely start with a letter, underscore(“_”) or “$” image
  • It could possibly include letters, numbers, underscore, or “$” image
  • A variable title can’t be a reserved key phrase.

JavaScript is a dynamically typed language so the kind of variables is determined at runtime. Subsequently there is no such thing as a have to explicitly outline the kind of a variable. We are able to declare variables in JavaScript in 3 ways:

Syntax:

var geek = "Whats up Geek"        // declaration utilizing var
let $ = "Welcome"            // declaration utilizing let
const _example = "Gfg"        // declaration utilizing const

All three key phrases do the fundamental process of declaring a variable however with some variations Initially, all of the variables in JavaScript have been written utilizing the var key phrase however in ES6 the key phrases let and const have been launched.

Instance 1: On this instance, we are going to declare variables utilizing var

Javascript

var a = "Whats up Geeks"

var b = 10;

var c = 12;

var d = b + c;

console.log(a);

console.log(b);

console.log(c);

console.log(d);

Output:

Whats up Geeks
10
12
22

Instance 2: On this instance, we are going to declare variables utilizing let 

Javascript

let a = "Whats up learners"

let b = "becoming a member of";

let c = " 12";

let d = b + c;

  

console.log(a);

console.log(b);

console.log(c);

console.log(d);

 
Whats up learners
becoming a member of
 12
becoming a member of 12

To study extra about JavaScript let verify this text JavaScript Let

Instance 3: On this instance, we are going to declare the variable utilizing the const key phrase

Javascript

const a = "Whats up learners"

console.log(a);

  

const b = 400;

console.log(b);

  

const c = "12";

console.log(c);

  

c = "new"

console.log(c)

Output:

 

Clarification: const key phrase is used after we assign a price completely to a variable. So after we attempt to change the worth of a variable declared with the const key phrase it’s going to throw an error. The variables declared with var and let are mutable that’s their worth will be modified however variables declared utilizing const are immutable. 

To study extra about JavaScript const verify this text JavaScript Const

Observe: The newly launched key phrases let and const are block scoped whereas var is operate scoped. 

Allow us to see an instance to grasp the distinction:

Instance:

Javascript

{

    let a = 2;

    var b = 4

    const c = "Whats up"

    console.log(a)

    console.log(b)

    console.log(c)

}

  

console.log(b)

console.log(c)

console.log(a

Output:

 

Clarification: Since variables “a” and “c” are block scoped so we weren’t in a position to entry them outdoors their block.

To study extra concerning the scope of variables confer with this text Understanding variable scopes in JavaScript

Comparability of properties of let, var, and const key phrases in JavaScript:

Property

var

let

const
Scope operate scoped block scoped block scoped
Updation mutable mutable immutable
Redeclarartion will be redeclared can’t be redeclared can’t be redeclared
Hoisting hoisted at prime hoisted at prime hoisted at prime

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