Hackforge Academy

Category: React • Beginner

Published on 18 Feb 2026

Explanation

#white-var has function scope, while let and const #white-have block scope.

Code Example

function test() {
  if (true) {
    var a = 1;
    let b = 2;
    const c = 3;
  }
  console.log(a); // Works
  // console.log(b); // Error
  // console.log(c); // Error
}

Explanation

#white-var allows redeclaration in the same scope. let #white-and const do not allow redeclaration.

Code Example

var x = 10;
var x = 20; // Allowed

let y = 10;
// let y = 20; // Error

const z = 10;
// const z = 20; // Error

Explanation

#white-var and let allow reassignment. const does not #white-allow reassignment after initialization.

Code Example

var a = 1;
a = 2; // Allowed

let b = 1;
b = 2; // Allowed

const c = 1;
// c = 2; // Error

Explanation

#white-var is hoisted and initialized with undefined. let #white-and const are hoisted but not initialized, leading #white-to Temporal Dead Zone.

Code Example

console.log(a); // undefined
var a = 10;

// console.log(b); // Error
let b = 20;

Explanation

#white-const must be initialized at declaration. var and #white-let can be declared without initialization.

Code Example

var a;
let b;

// const c; // Error
const c = 5;

Explanation

#white-Use const by default. Use let if the #white-value needs to change. Avoid var in modern #white-JavaScript.

Code Example

const pi = 3.14;
let counter = 0;

counter++;