Difference Between Shallow Copy and Deep Copy in JavaScript

Understanding Shallow Copy vs Deep Copy in JavaScript

Copying objects in JavaScript isn’t always simple.
There are two types of copying:

Shallow Copy

• Copies only the first level.
• Nested objects are still referenced.
• Changes inside nested objects affect both copies.

Deep Copy

• Copies everything, including nested objects.
• No shared references.
• Changes in one object do not affect the other.

Example

const obj1 = { name: "John", address: { city: "Delhi" } };

const obj2 = { ...obj1 }; // Shallow copy

obj2.address.city = "Mumbai";

console.log(obj1.address.city); 
// Mumbai (changed!)

This happens because nested objects are shared.

Simple Explanation

Shallow copy = shared inner objects
Deep copy = completely separate objects