What are JavaScript Data Types ? See Examples

JavaScript uses different data types to store and manipulate information. Knowing these types is essential for writing efficient and bug-free code. Data types are divided into primitive and non-primitive types.

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1. Primitive Data Types

Primitive types are simple, immutable values stored directly in memory.

• String: Represents textual data. Strings are enclosed in single ('), double (") or backticks (`).

let name = "Alice";
let greeting = `Hello, ${name}!`; // Template literals

• Number: Represents integers or floating-point numbers.

let age = 30;
let price = 19.99;

• Boolean: Represents true or false. Often used in conditional statements.

let isActive = true;
if(isActive){
    console.log("User is active");
}

• Undefined: A variable declared but not assigned a value.

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

• Null: Represents intentional absence of a value.

let selectedItem = null;

• Symbol: A unique and immutable value, often used for object property keys.

let id = Symbol("id");

• BigInt: Used for integers larger than Number.MAX_SAFE_INTEGER.

let bigNumber = 123456789012345678901234567890n;

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2. Non-Primitive (Reference) Data Types

These data types store complex data and are mutable.

• Array: Stores ordered collections of values of any type. Arrays come with many built-in methods for manipulation.

let colors = ["red", "green", "blue"];
colors.push("yellow"); // Add element
console.log(colors[2]); // "blue"

• Object: Stores key-value pairs and is used for structured data. Objects can contain strings, numbers, booleans, arrays, functions, or even other objects.

let user = { 
    name: "Alice", 
    age: 30, 
    isActive: true, 
    hobbies: ["reading", "gaming"]
};
console.log(user.hobbies[1]); // "gaming"

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3. Checking Data Types

JavaScript provides the typeof operator to check the type of a variable.

console.log(typeof name);  // "string"
console.log(typeof age);   // "number"
console.log(typeof user);  // "object"

Tip: Arrays are technically objects, so typeof [] returns "object". To check arrays specifically, use Array.isArray(arr).

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4. Practical Notes

• Primitive values are immutable — changing a variable creates a new value in memory.
• Objects and arrays are reference types — multiple variables can point to the same object, which may lead to unexpected changes if not handled carefully.
• Understanding data types is crucial for debugging, performing operations, and handling user input in web applications.

Mastering data types in JavaScript is the foundation for everything — from variables and operators to functions and objects.

Citations:

• Learn JavaScript – Savanka
• JavaScript Tutorial – W3Schools