Hackforge Academy

Explanation

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

Code:

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

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

Code:

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

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

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

Explanation

var and let allow reassignment. const does not
allow reassignment after initialization.

Code:

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

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

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

Explanation

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

Code:

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

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

Explanation

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

Code:

var a;
let b;

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

Explanation

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

Code:

const pi = 3.14;
let counter = 0;

counter++;