JavaScript Data Types: A Comprehensive Guide

Data Type	Description	Example
String	Represents text enclosed in quotes.	let name = "john";
Number	Represents numeric values (integer or float).	let age = 25;
BigInt	Represents large integers beyond `Number.MAX_SAFE_INTEGER`.	let bigNum = 12345678901234567890n;
Boolean	Represents true or false values.	let isActive = true;
Undefined	A variable declared but not assigned a value.	let x;
Null	Represents an intentional absence of value.	let data = null;
Symbol	Represents unique and immutable identifiers.	let id = Symbol('id');

Example of Primitive Data Types:

let name = "Alice"; // String

let age = 30; // Number

let bigInt = 9007199254740991n; // BigInt

let isAvailable = true; // Boolean

let notAssigned; // Undefined

let emptyValue = null; // Null

let sym = Symbol('key'); // Symbol

Non-Primitive (Reference) Data Types:

Non-primitive types are mutable and stored as references in memory.

Data Type	Description	Example
Object	A collection of key-value pairs.	let obj = {name: "John"};
Array	A list-like structure for storing multiple values.	let arr = [1, 2, 3];
Function	A block of reusable code.	function greet() { console.log('Hello'); }
Date	Represents dates and times.	let date = new Date();

Example of Non-Primitive Data Types

let person = { name: "Bob", age: 25 }; // Object

let colors = ["red", "blue", "green"]; // Array

function greet() { console.log("Hello!"); } // Function

let currentDate = new Date(); // Date

Dynamic Typing:

JavaScript is dynamically typed, meaning variables can hold values of any type.

Example

let value = 42; // Number

value = "Hello"; // String

value = true; // Boolean

Type Checking:

To check a variable's data type, use the typeof operator:

Example

console.log(typeof "Hello"); // String

console.log(typeof 42); // Number

console.log(typeof true); // Boolean

console.log(typeof undefined); // Undefined

console.log(typeof null); // Object (known JavaScript bug)

console.log(typeof Symbol()); // Symbol

console.log(typeof {}); // Object

console.log(typeof []); // Object (Array is a subtype of Object)

console.log(typeof function(){}); // Function

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Primitive Data Types:

Data Type

Description

Example

Non-Primitive (Reference) Data Types:

Data Type

Description

Example

Dynamic Typing:

Type Checking: