JavaScript Data Types

Variables hold values, and every value has a specific data type that defines the kind of information it holds. These data types are broadly categorized into two groups: Primitive Data Types and Non-Primitive Data Types.

Data types are categorized into Primitive and Non-Primitive (Reference) types in JavaScript.

Primitive

When you assign a primitive value:

• It is stored directly in memory
• Copying the value creates a new independent value

They are immutable, meaning you cannot change the value itself—only replace it.

JavaScript has 7 primitive types:

1. Number

All numbers (integer or floating point).

let x = 10;
let y = 11.5;

2. String

Text data.

let name = "Hello World!";

3. Boolean

True or False.

let isOnline = true;

4. Null

Intentional empty value.

let data = null;

5. Undefined

A variable declared but not assigned a value.

let a; // undefined

6. Symbol

Symbol data type is used to create objects that will always be unique. These objects can be created using Symbol constructor.

let sym = Symbol("Hello")
console.log(typeof(sym)); // Symbol
console.log(sym); // Hello

7. BigInt

For very large integers beyond Number’s limit.

let big = 12345678901234567890n;

---

Non-Primitive (Reference)

This data type is mutable, which means you can change/modify it. Allows you to modify existing values without creating new ones.

Non-primitive values are stored by reference. When you assign an object to another variable, JavaScript copies the reference, not the value.

These are objects—more complex data structures. The main non-primitive types:

• Object
• Array (actually a special type of object)
• Function (also an object)
• Date
• Map, Set, etc. (still objects)

let obj1 = { age: 27 };
let obj2 = obj1;

obj2.age = 30;

console.log(obj1.age); // 30 (obj1 also changed)

Why? Because both variables point to the same memory address.