Difference between let var const

Question

Accepted Answer

let, var, and const are JavaScript keywords used for declaring variables with different scoping and mutability.

let and const were introduced in ES6 while var has been used since the beginning of JavaScript.
let and const have block-level scoping while var has function-level scoping.
let and var are mutable while const is immutable.
let can be reassigned while const cannot be reassigned.
const must be initialized during declaration while let and var can be initialized later.
Example: let x = 5; var y = 10; const z = 'hello';
Example: function example() { var x = 5; if (true) { let y = 10; const z = 'hello'; } }
Example: const arr = [1, 2, 3]; arr.push(4); // valid, arr = [1, 2, 3, 4]; // invalid

Popular interview questions of Software Engineer