What is a Variable?

A variable is a container that stores data.

Example

let age = 20;

let → keyword
age → variable name
20 → value

var, let, const

1. `var` (OLD WAY – avoid in modern JS)

var name = "John";

❌ Problems:

Function scoped (not block scoped)
Can be re-declared
Causes bugs

var x = 10;
var x = 20; // ✅ allowed (but dangerous)

2. `let` (MODERN – use this )

let age = 25;

✅ Features:

Block scoped
Can be updated
Cannot be re-declared

let x = 10;
x = 20; // ✅ allowed

let x = 30; // ❌ error

3. `const` (CONSTANT – most used )

const pi = 3.14;

✅ Features:

Block scoped
Cannot be updated
Cannot be re-declared

const x = 10;
x = 20; // ❌ error

When to use what?

const → default choice ✅
let → if value changes
var → ❌ avoid