1. JavaScript Data Types

🧠JavaScript Data Types

What is a Data Type?

A data type tells JavaScript what kind of value a variable holds.
A variable is a container that stores a value — like a number, text, or object.
Data types help programs understand how to use that data.

🧩 Basic Data Types in JavaScript

1. Number

Used for integers and decimal (floating-point) numbers.

let age = 25;
const pi = 3.14;
Examples: 7, 19, 90, 3.14, 5.2

2. String

Represents text, written inside quotes.

let greeting = "Hello, world";
let language = 'JavaScript';

3. Boolean

Represents true or false values.

let isLoading = false;
let isLoggedIn = true;

4. undefined

A variable declared but not given a value yet.

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

5. null

A variable that is intentionally set to nothing.

let user = null;

6. Object

A complex data type that stores key-value pairs.

let book = {
title: "The Great Gatsby",
author: "F. Scott Fitzgerald",
year: 1925
};
Keys = property names (title, author, year)
Values = data they hold ("The Great Gatsby", etc.)
Each key-value pair is called a property.

7. Symbol

A unique and immutable (unchangeable) value.

const symbol1 = Symbol('mySymbol');
const symbol2 = Symbol('mySymbol');
console.log(symbol1 === symbol2); // false

8. BigInt

Used for very large numbers that go beyond Number’s limit.

const bigNumber = 1234567890123456789012345678901234567890n;
console.log(bigNumber);

🧾 Summary

Data Type	Example	Description	Real-World Use
Number	`let price = 499.99;`	Represents numeric values (integers or decimals)	Tracking a product’s price, temperature, or age
String	`let name = "John Doe";`	Text or sequence of characters	Storing usernames, messages, or display text
Boolean	`let isOnline = true;`	Logical value: `true` or `false`	Checking if a user is logged in, dark mode on/off
undefined	`let phone;`	Declared but not assigned a value	Variable waiting for user input or API data
null	`let selectedItem = null;`	Empty on purpose — no value yet	Resetting variables or clearing form fields
Object	`let user = { name: "Liya", age: 20 };`	Group of related data (key-value pairs)	Representing user profiles, products, cars, etc.
Symbol	`const token = Symbol('id');`	Unique identifier, never duplicated	Creating private keys or unique property names
BigInt	`let bigNum = 98765432109876543210n;`	Very large integers beyond normal Number limit	Handling financial data, scientific calculations