How does garbage collection work in JavaScript?

Question

How does garbage collection work in JavaScript?

Answer

JavaScript has automatic garbage collection.
It uses a reachability model — if an object is no longer reachable from the root (like window or the global scope), it becomes garbage and is eligible for cleanup.

let user = { name: 'Ghazi' };
user = null; // object is no longer referenced → can be collected

Modern JS engines (V8, SpiderMonkey) use mark-and-sweep:

1. Start from roots
2. Mark all reachable objects
3. Sweep unmarked ones

Real-World Example

Memory leaks often happen when we keep references in:

• global variables
• long-lived closures
• DOM elements not removed from code

Quick Practice

Create an object, reference it in an array, then remove all references and explain when it becomes collectible.

Summary

GC in JS is automatic but not magic — your job is to avoid holding unnecessary references.