Understanding Variables in JavaScript

1. A Simple Idea

Think of a variable like a box.

You can store something inside it, give it a name, and use it later.

Example:

let name = "Aman";

• name → box name

• "Aman" → value inside the box

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2. Why Variables Are Needed

Instead of writing values again and again:

console.log("Aman");
console.log("Aman");

You store it once:

let name = "Aman";

console.log(name);
console.log(name);

This makes code easier to manage.

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3. Declaring Variables

JavaScript provides three ways:

var a = 10;
let b = 20;
const c = 30;

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4. Primitive Data Types

String (text)

let name = "Aman";

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Number

let age = 21;

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Boolean

let isStudent = true;

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Null

let data = null;

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Undefined

let value;

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5. Difference Between var, let, and const

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Simple Explanation

• var → old way (avoid using)

• let → can change value

• const → cannot change value

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6. Changing Values

let (allowed)

let age = 21;
age = 22;

console.log(age); // 22

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const (not allowed)

const pi = 3.14;
pi = 3.15; // error

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7. What is Scope (Simple)

Scope means:

👉 Where a variable can be used

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Example

{
  let x = 10;
  console.log(x); // works here
}

console.log(x); // error

9. Practice Assignment

Declare variables

let name = "Aman";
let age = 21;
let isStudent = true;

console.log(name);
console.log(age);
console.log(isStudent);

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Try changing values

let age = 21;
age = 25; // works

const name = "Aman";
name = "Rahul"; // error