JavaScript Data Types Explained with Examples

JavaScript is a dynamically typed language, which means you don’t have to specify the data type of a variable when declaring it. The type is determined automatically based on the value assigned to it.

JavaScript has eight data types, divided into two main categories:

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

1. Primitive Data Types

Primitive data types represent a single value and are immutable (cannot be changed).

The primitive types are:

• String
• Number
• Boolean
• Undefined
• Null
• Symbol
• BigInt

Let’s understand each one in detail.

1.1 String

A string is a sequence of characters used to represent text. Strings can be enclosed in single quotes ('), double quotes ("), or backticks (`).

Example:

let firstName = "John";
let message = 'Welcome to JavaScript!';
let greeting = `Hello, ${firstName}!`; // Template literal

console.log(firstName);    // John
console.log(message);      // Welcome to JavaScript!
console.log(greeting);     // Hello, John!
console.log(typeof firstName); // string

1.2 Number

The number type is used for both integers and floating-point numbers. JavaScript does not distinguish between integer and decimal values.

Example:

let age = 25;
let price = 99.5;
let temperature = -10;

console.log(age + price); // 124.5
console.log(typeof price); // number

1.3 Boolean

A boolean type represents only two possible values: true or false. It is commonly used for decision-making and condition checking.

Example:

let isOnline = true;
let isVerified = false;

console.log(isOnline);      // true
console.log(typeof isOnline); // boolean

if (isOnline) {
    console.log("User is online");
}

1.4 Undefined

A variable that has been declared but has not been assigned a value is of type undefined.

Example:

let city;
console.log(city); // undefined
console.log(typeof city); // undefined

1.5 Null

The null type represents the intentional absence of any value. It must be assigned manually by the developer.

Example:

let user = null;
console.log(user); // null
console.log(typeof user); // object (this is a known JavaScript bug)

1.6 Symbol

Introduced in ES6, the symbol type is used to create unique identifiers. Symbols are often used as object keys to avoid name conflicts.

Example:

let id1 = Symbol("id");
let id2 = Symbol("id");

console.log(id1 === id2); // false
console.log(typeof id1); // symbol

1.7 BigInt

The BigInt type allows working with very large integers beyond the limit of the Number type (which is 2^53 - 1).

Example:

let bigNumber = 1234567890123456789012345678901234567890n;

console.log(bigNumber);
console.log(typeof bigNumber); // bigint

2. Non-Primitive (Reference) Data Types

Non-primitive data types can store multiple values and are mutable. They include objects, arrays, and functions.

2.1 Object

An object is a collection of key-value pairs. Each key is a property, and each property has a value.

Example:

let student = {
    name: "Alice",
    age: 22,
    course: "JavaScript"
};

console.log(student.name); // Alice
console.log(typeof student); // object

2.2 Array

An array is a special type of object used to store an ordered list of values.

Example:

let fruits = ["Apple", "Banana", "Mango"];
console.log(fruits[0]); // Apple
console.log(typeof fruits); // object

2.3 Function

A function is an object that can be invoked to perform a specific task.

Example:

function greet(name) {
    return "Hello, " + name + "!";
}

console.log(greet("John")); // Hello, John!
console.log(typeof greet); // function

Summary Table

Live Example: Testing All Data Types Together

You can try this code in your browser console:

let name = "Sara";                 // String
let age = 28;                      // Number
let isStudent = true;              // Boolean
let score;                         // Undefined
let car = null;                    // Null
let uniqueKey = Symbol("id");      // Symbol
let bigValue = 9007199254740991n;  // BigInt
let person = { name, age };        // Object

console.log(typeof name, name);
console.log(typeof age, age);
console.log(typeof isStudent, isStudent);
console.log(typeof score, score);
console.log(typeof car, car);
console.log(typeof uniqueKey, uniqueKey);
console.log(typeof bigValue, bigValue);
console.log(typeof person, person);