What is garbage collector in JavaScript?
Garbage Collector is a built-in mechanism in JavaScript that automatically manages memory. It's responsible for freeing memory occupied by objects that are no longer used in the program.
You don't manage memory manually — JavaScript engine does it for you (e.g., V8 in Chrome/Node.js).
How Does Garbage Collector Work?
JavaScript allocates memory for variables and objects when they're created, and frees it when they're no longer reachable.
Main principle:
Object is considered "garbage" if there are no more references to it.
Example:
let user = { name: "Alice" };
user = null; // Now object can be deleted from memoryAlgorithms Used in GC
Mark-and-Sweep
Most common algorithm:
- Marks all objects accessible through variables (root objects).
- All other objects are deleted as "garbage".
window / global variables
Object A
Object B
Object C (unreachable)
In this example object C is unreachable and will be deleted.
Reference Counting
Each object stores a number showing how many references point to it. If counter = 0, object is deleted.
Disadvantage: circular references aren't deleted.
let a = {};
let b = {};
a.ref = b;
b.ref = a;
// Both variables are null, but objects still reference each other
a = null;
b = null; // Potential memory leak!How to Avoid Memory Leaks?
- Remove unused timers:
clearInterval,clearTimeout - Clear subscriptions, event handlers
- Nullify large objects and DOM references:
ref.current = null - Avoid global variables
- Use
WeakMap,WeakSet— they don't prevent garbage collection
Signs of Memory Leaks
- Constant memory growth during use
- Delays, freezes, lags
- High RAM consumption in DevTools →
Performance/Memorytab
Important:
Garbage collection in JavaScript is not instant — it's a process that runs periodically. So memory freeing can happen with delay.
Short Answer
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