1. What Are Variables?

In programming, variables are like containers (or boxes) used to store information.
Just like you keep items in a box and label it, in JavaScript we store data in variables with a name.

Example in real life:

• A box labeled Name stores "John"

• A box labeled Age stores 25

Example in JavaScript:

let name = "John";
let age = 25;

Here:

• name stores a text value

• age stores a number

Variables help us store and reuse data in our program.

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2. Declaring Variables (var, let, const)

JavaScript provides three ways to create variables.

1. var

The older way to declare variables.

var city = "Bangalore";

2. let

The modern and most commonly used way.

let age = 25;

You can change the value later.

let age = 25;
age = 26;

3. const

Used when the value should not change.

const country = "India";

If you try to change it:

country = "USA"; // Error

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3. Primitive Data Types in JavaScript

JavaScript has some basic data types called primitive data types.

1. String (Text)

Used to store text.

let name = "Sintu";

Examples:

• "Hello"

• "JavaScript"

• "Student"

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2. Number

Used for numeric values.

let age = 22;
let price = 99.5;

Examples:

• 10

• 45

• 3.14

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3. Boolean

Represents true or false.

let isStudent = true;

Examples:

• true

• false

Used mostly in conditions.

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4. Null

Represents an empty or intentionally cleared value.

let data = null;

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5. Undefined

Means the variable exists but has no value assigned yet.

let score;
console.log(score); // undefined

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4. Difference Between var, let, and const

Keyword	Can Change Value?	Modern Usage
var	Yes	Mostly avoided
let	Yes	Recommended
const	No	Used for fixed values

Example:

let age = 20;
age = 21; // allowed

const birthYear = 2000;
birthYear = 2001; // error

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5. What Is Scope? (Simple Explanation)

Scope means where a variable can be used in your code.

Example:

{
  let message = "Hello";
  console.log(message);
}

console.log(message); // Error

Here, message only exists inside the block { }.

Think of scope like a room:

• If you keep something inside the room, you can only use it inside that room.

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Small Example

let name = "Sintu";
let age = 22;
const country = "India";

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

Output:

Sintu
22
India

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Assignment

Create variables for the following:

• Name

• Age

• IsStudent

Example:

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

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