JavaScript Coding Day 8 | Primitive Data Types & Non-Primitive Data Types

Primitive Data Types & Non-Primitive Data Types

Watch the lesson tutorial  🔻

1. Primitive Data Types

Primitive data types are the simplest forms of data. In JavaScript, they are immutable (cannot be changed) and strictly stored by value. When you assign a primitive value to a new variable, JavaScript creates a completely separate copy of that value.

Common Primitive Types: Number, String, Boolean, Undefined, Null.

Practical Example (Pass by Value)

In this example, b becomes a copy of a. Because they are primitive, they are independent of each other.

JavaScript

let a = 50;
let b = a;   // JavaScript creates a copy of the value 50 for 'b'
b = 60;      // Changing 'b' does not affect 'a'

console.log(a); 

// Output: 50
// Reason: Primitive data types are passed by "Value". 
// When we said 'let b = a', 'b' got its own copy of the number 50. 
// Modifying 'b' essentially changes the copy, leaving the original 'a' untouched.

---

2. Non-Primitive Data Types

Non-primitive data types (often called Reference Types) are more complex. They include Objects, Arrays, and Functions.

Instead of storing the actual data directly in the variable, JavaScript stores a reference (a memory address) that points to where the data is stored in memory (the Heap). When you copy a non-primitive, you are only copying the address, not the actual object.

Practical Example (Pass by Reference)

In this example, both o and p point to the exact same object in memory.

JavaScript

const o = { name: "Chiru" };
const p = o;          // 'p' receives the REFERENCE (address) to the same object as 'o'
p.name = "ChiruCodes"; // We change the data inside that shared memory location

console.log(o);

// Output: { name: "ChiruCodes" }
// Reason: Non-primitive data types are passed by "Reference". 
// 'o' and 'p' are like two different keys opening the exact same door. 
// If you use key 'p' to open the room and rearrange the furniture (change the name), 
// the room looks different when you look through key 'o'.

---

Difference: Primitive vs. Non-Primitive

Here is a comparison table to summarize the differences for your readers.

Feature	Primitive Data	Non-Primitive Data
Examples	Number, String, Boolean, Null	Object, Array, Function
Storage	Stores the actual value.	Stores a reference (address) to the value.
Mutability	Immutable (cannot be changed).	Mutable (can be modified).
Comparison	Compared by value (5 === 5 is true).	Compared by reference ([] === [] is false).
Memory	Stored in the Stack.	Stored in the Heap.

Run Today's Lesson Codes on NextLeap (Click Here)

- by Chirana Nimnaka