Data Types in JavaScript
In JavaScript, data types tell the language what kind of value a variable is holding. Understanding data types is super important because it affects how your code behaves.
JavaScript is dynamically typed, so you don’t need to declare a type — the interpreter figures it out for you.
let name = "Alice"; // JavaScript knows this is a string
1. Primitive Data Types
Primitive types are the most basic data types. They store single values and are immutable (can’t be changed after creation).
Data Type | Example | Description |
---|---|---|
String | "Hello" | Text, always inside quotes |
Number | 42, 3.14 | Integer or decimal numbers |
Boolean | true, false | Logical values (yes/no, on/off) |
Undefined | let x; |
A variable that’s declared but not set |
Null | let y = null; |
Represents no value (empty) |
BigInt | 12345678901234567890n | For really big numbers |
Symbol | Symbol("id") |
Unique value, useful for object keys |
2. Non-Primitive (Reference) Data Types
These types store collections or complex structures of data.
JavaScript Data Types
Data Type | Example | Description |
---|---|---|
Object | { name: "John", age: 30 } | Collection of key-value pairs |
Array | [1, 2, 3, 4] | Ordered list of items |
Function | function greet() {} | Block of code that can be reused |
Date, RegExp | Built-in objects | Used for specific tasks |
type of Operator
Use typeof to find out what data type a variable is:
let age = 25;
console.log(typeof age); // "number"
let user = { name: "Alice" };
console.log(typeof user); // "object"
Examples of Different Data Types
let name = "Alice"; // String
let age = 30; // Number
let isLoggedIn = true; // Boolean
let email; // Undefined
let car = null; // Null
let id = Symbol("unique"); // Symbol
let big = 1234567890123456789n; // BigInt
let colors = ["red", "green"]; // Array
let person = { name: "John", age: 30 }; // Object
function greet() { return "Hi!"; } // Function