JavaScript Data Types (Basics)

JavaScript data types define the kind of value a variable can hold.

👉 There are two main categories:

1. Primitive Data Types
2. Non-Primitive (Reference) Data Types

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🔹 1. Primitive Data Types

Primitive types store single values and are immutable.

✅ 1. Number

Represents both integers and floating-point numbers.

let age = 25;
let price = 99.99;

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✅ 2. String

Represents text (inside quotes).

let name = "Deepesh";
let message = 'Hello World';

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✅ 3. Boolean

Represents true or false.

let isLoggedIn = true;
let isAdmin = false;

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✅ 4. Undefined

A variable declared but not assigned a value.

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

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✅ 5. Null

Represents intentional absence of value.

let data = null;

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✅ 6. BigInt

Used for very large integers.

let bigNumber = 123456789012345678901234567890n;

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✅ 7. Symbol

Used for unique identifiers.

let id = Symbol("userId");

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🔹 2. Non-Primitive (Reference) Data Types

These store collections or complex data.

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✅ 1. Object

Key-value pairs.

let user = {
  name: "Deepesh",
  age: 25,
  isActive: true
};

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✅ 2. Array

Ordered list of values.

let fruits = ["apple", "banana", "mango"];

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✅ 3. Function

A block of reusable code.

function greet() {
  return "Hello!";
}

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🔹 typeof Operator

Used to check the data type.

console.log(typeof 10);          // number
console.log(typeof "Hello");     // string
console.log(typeof true);        // boolean
console.log(typeof undefined);   // undefined
console.log(typeof null);        // object (known JS bug)
console.log(typeof {});          // object
console.log(typeof []);          // object

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⚠️ Important Notes

• null returns "object" → historical bug in JavaScript
• Arrays are technically objects
• Functions are also treated as objects

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🧠 Quick Summary Table

Type	Example
Number	10, 3.14
String	"Hello"
Boolean	true, false
Undefined	let x;
Null	null
BigInt	123n
Symbol	Symbol("id")
Object	{name: "John"}
Array	[1,2,3]
Function	function(){}

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🚀 Simple Example Combining All

let user = {
  name: "Deepesh",     // string
  age: 25,             // number
  isLoggedIn: true,    // boolean
  balance: 1000000000000000000n, // BigInt
  id: Symbol("id"),    // symbol
  hobbies: ["coding", "music"], // array
  address: null        // null
};console.log(typeof user);