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What's the difference between using 'let' and 'var'?

JavaScript | let vs var: In this tutorial, we will learn about the difference between using 'let' and 'var'.
Submitted by Pratishtha Saxena, on May 20, 2022

JavaScript 'let' Keyword

This is used to declare variables in JavaScript. It is block-scoped which means it can only be accessed inside a block of code. Block in nothing but some code written within {} brackets. So, variable declared with let is only available to use inside that block.

We see that using let variable outside its block (the curly braces where it was defined) returns an error. This is because let variables are block scoped.

Syntax:

let a = 'value';

Example 1:

// variable name cannot be used here
function person() {
	let name = 'John';

	// variable age cannot be used here
	if (name == 'John') {
		// variable age can be used here
		let age = '20';
		console.log(name + ' ' + age);
	}

	// variable age cannot be used here
	console.log(name + ' ' + age); // will return error
}

// variable name cannot be used here

person();

Output:

Uncaught ReferenceError: age is not defined
    at person (<anonymous>:13:27)
    at <anonymous>:18:1

JavaScript 'var' Keyword

This is also used to declare a variable. The var keyword is used here. The variable declared inside a function with var can be used anywhere within a function. Hence, it is function-scoped. Once the variable is declared with var. The variable can be used anywhere inside the function.

It is also called globally-scoped. The scope is global when a var variable is declared outside a function. This means that any variable that is declared with var outside a function block is available for use in the whole window.

Syntax:

var b = 'value';

Example 2:

// variable name cannot be used here

function person() {
	// variable name can be used here
	var name = 'Tom';
	console.log(name);
}

// variable name cannot be used here

person();

Output:

Tom

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