What is the difference between let, var and const in JavaScript?

With JavaScript, the user can declare variables with three keywords, which are let, var, and const. The terms var let and const are somewhat confusing. We will explain all 3 variables with the help of examples.

The difference between the variables var, let as well as const is described below in different ways.

• Scope
• Hoisting
• Reassign the value
• Redeclaration of the variable

1. Scope

var	let	const
It's a function scope	block scope	block scope

Function scope example

const func = () => {
    var val1 = 5;
    if(true) {
        var val2 = 10;
        console.log(val1); //Output 5
        console.log(val2); //Output 10
    }
}
func();
console.log(val1); //undefined. Not available outside function
console.log(val2); //undefined. Not available outside function

Block scope example

const func = () => {
    let x = 10;
    if(x === 10) {
        let y = 20;
        console.log(x); //Output 10
        console.log(y); //Output 20
    }
    console.log(x); // Output 10
    console.log(y); // ’undefined'
}
func();

2. Hoisting

Hoisting is the term used to define a variable prior to its declaration.

var	let	const
Allowed	Not allowed	Not allowed
var1 = 100;  console.log(var1); var var1; // 100	let1 = 100;  console.log(let1); let let1; // ReferenceError: let1 is not defined	const1 = 100;  console.log(const1); const const1; // SyntaxError: Missing initializer in const declaration

3. Reassign the value

var	let	const
Allowed	Allowed	Not allowed

4. Redeclaration the value

var	let	const
Allowed	Not Allowed	Not allowed