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How to declare Global Variables in JavaScript ?

How to declare variables in different ways in JavaScript?

Last Updated : 06 Sep, 2024

In JavaScript, variables can be declared using keywords like var, let, or const, each keyword is used in some specific conditions. Understanding these declarations is crucial for managing variable lifetimes and avoiding unintended side effects in code.

Table of Content

JavaScript var

This keyword is used to declare variables globally. If you use this keyword to declare a variable then the variable can be accessible globally and changeable also. It is good for a short length of codes, if the codes get huge then you will get confused.

Syntax:

var variableName = "Variable-Value;"

Example: This example shows the use of var.

javascript

var geeks = "GeeksforGeeks"; console.log(geeks);

Output

GeeksforGeeks

JavaScript let

This keyword is used to declare variables locally. If you use this keyword to declare a variable then the variable can be accessible locally and it is changeable as well. It is good if the code gets huge.

Syntax:

let variableName = "Variable-Value;"

Example: This example shows the use of let.

javascript

if (true) {     let geeks = "GeeksforGeeks";     console.log(geeks); }  /* This will be error and     show geeks is not defined */ console.log(geeks);

Output

GeeksforGeeks

JavaScript const

This keyword is used to declare variable locally. If you use this keyword to declare a variable then the variable will only be accessible within that block similar to the variable defined by using let and difference between let and const is that the variables declared using const values can’t be reassigned. So we should assign the value while declaring the variable.

Syntax:

const variableName = "Variable-Value;"

Example: This example shows the use of const.

javascript

const geeks = "GeeksforGeeks"; console.log(geeks);

Output

GeeksforGeeks

Difference Between var, let, and const

JavaScript var	JavaScript let	JavaScript const
Can be redeclared	Cannot be redeclared	Cannot be redeclared
Can be reassigned a value	Can be reassigned a value	Cannot reassign the value
Only have global and function scope	Can have a block scope	Can have a block scope
Variables are hoisted on top and can be used anywhere	Variables must be initialized before use	Variables must be initialized before use
Can be redeclared anywhere in the program	Cannot be redeclared inside a block	Cannot be redeclared inside a block

How to declare Global Variables in JavaScript ?

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