JavaScript Variables – GeeksforGeeks

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

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

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

JavaScript is a dynamically typed language so the kind of variables is set at runtime. Subsequently there isn’t a must explicitly outline the kind of a variable. We are able to declare variables in JavaScript in 3 ways:

Syntax:

var geek = "Good day Geek"        // declaration utilizing var
let $ = "Welcome"            // declaration utilizing let
const _example = "Gfg"        // declaration utilizing const   

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

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

Output:

Good day Geeks
10
12
22

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

Good day learners
becoming a member of
 12
becoming a member of 12

To be taught extra about JavaScript let examine this text JavaScript Let

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

Output:

 

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

To be taught extra about JavaScript const examine this text JavaScript Const

Be aware: 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:

Output:

 

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

To be taught 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: