Memory Leaks and Garbage Collection in Node.js: What Developers Get Wrong (And How to Fix It)

Table of contents
- Introduction: Is Node.js Really Leaking Memory?
- How Garbage Collection Works in Node.js (V8)
- Common Causes of Memory Leaks in Node.js (And How to Fix Them)
- Let’s Visualize Memory Leak Lifecycle in Node.js
- How to Detect and Debug Memory Leaks
- How to Prevent Memory Leaks in Node.js
- Node.js Isn't the Problem — It's the Patterns
- Conclusion: Own Your Memory
- 📣 Want More?

Introduction: Is Node.js Really Leaking Memory?
Have you ever noticed your Node.js app using more and more memory over time — even when it seems like nothing is wrong? You’re not alone.
Memory leaks and confusing garbage collection behavior often lead developers to believe Node.js is the problem. But in most cases, the real cause is subtle: a lingering reference, a never-cleared timer, or a quiet EventEmitter listener.
In this post, we’ll break down:
How garbage collection works in Node.js
What typically causes memory leaks
How to detect and fix them with the right tools
How Garbage Collection Works in Node.js (V8)
Node.js is powered by Google’s V8 engine, which has a highly optimized garbage collector.
This shows how V8’s garbage collector handles object lifecycles across its young and old generations.
graph TD
A[New Object Created] --> B[Allocated in Young Generation]
B --> C{Survives GC Cycle?}
C -- No --> D[🧹 Collected]
C -- Yes --> E[Promoted to Old Generation]
E --> F{Still Reachable?}
F -- No --> G[✅ Collected Later]
F -- Yes --> H[♻️ Retained in Memory]
Figure: Memory leaks happen when objects stay referenced unnecessarily
Key Concepts:
Automatic memory management: You don’t
free()
memory like in C or C++.Reachability-based GC: If an object is no longer reachable (via variables, closures, globals), it’s eligible for garbage collection.
Generational GC:
Young Generation: Short-lived objects are collected quickly.
Old Generation: Long-lived objects (like cached data) are collected more slowly.
Example:
let user = { name: "Alice" };
user = null; // Now eligible for garbage collection
💡 Garbage collection only works when we let go of objects. If we accidentally hold references, the GC can’t help us.
Common Causes of Memory Leaks in Node.js (And How to Fix Them)
Let’s Visualize Memory Leak Lifecycle in Node.js
This diagram visualizes how memory leaks occur when objects stay "reachable" due to poor cleanup or design choices.
flowchart TD
A[Object Created in App] --> B{Still Referenced?}
B -- No --> C[✅ GC Reclaims Memory]
B -- Yes --> D[♻️ Object Stays in Memory]
D --> E{Why Still Referenced?}
E --> F[Held by Global or Static Variable]
E --> G[Captured in Closure]
E --> H[Stored in Cache/Map]
E --> I[Attached to EventEmitter]
E --> J[Uncleared setInterval/setTimeout]
F --> K[⚠️ Memory Leak Risk]
G --> K
H --> K
I --> K
J --> K
K --> L[Memory Usage Grows Over Time]
Figure: V8’s GC works in generations — long-lived objects live longer, but must still be released to be collected.
Even experienced developers can run into these:
1. Global or Static References
The problem: Declaring large objects or caches on global
, module.exports
, or top-level scope that never get cleared.
global.myCache = {}; // Stays alive for the life of the app
✅ Solution: Use scoped caches or implement manual expiration logic:
const cache = new Map();
function storeWithTTL(key, value, ttl = 60000) {
cache.set(key, value);
setTimeout(() => cache.delete(key), ttl);
}
Or use WeakMap
if the reference should be GC’d automatically when keys disappear:
const weakCache = new WeakMap();
2. Growing Arrays or Maps Unbounded Without Cleanup
The problem:
Large in-memory collections that grow indefinitely with no cap.
const cache = {};
function store(key, value) {
cache[key] = value; // Grows forever if not cleaned up
}
✅ Solution: Limit memory usage with:
Size caps
LRU strategies
Eviction policies
Example using lru-cache
:
const LRU = require('lru-cache');
const cache = new LRU({ max: 1000 }); // only stores 1000 items
3. EventEmitter Listeners That Aren’t Removed
The problem: Listeners accumulate over time and are never removed, especially in dynamic contexts.
emitter.on('data', () => {}); // Never removed
Too many listeners can also trigger the "MaxListenersExceededWarning" error.
✅ Solution:
Use
.once()
if only needed onceTrack and remove listeners when done
Or use cleanup functions:
function onData(data) { /* ... */ }
emitter.on('data', onData);
// Later...
emitter.removeListener('data', onData);
🧠 Bonus: Set emitter.setMaxListeners(n)
to avoid warnings (but don't suppress blindly).
4. Closures That Hold Onto Big Objects
The problem: Closures accidentally retain large objects by referencing them inside long-lived functions.
function outer() {
const bigData = { /* ...large object... */ };
return function inner() {
console.log(bigData); // Closure keeps bigData alive
};
}
✅ Solution:
Avoid capturing unnecessary data in closures
Extract logic to use only what’s needed
Consider functional patterns that limit lifespan
Example:
function logField({ name }) {
console.log(name); // Avoid referencing full object
}
5. Uncleared Intervals and Timeouts
The problem: Timers keep running even after a request or component is done.
setInterval(() => {
// logic
}, 1000); // Will run forever unless cleared
✅ Solution: Always store the ID and clear it during teardown:
const intervalId = setInterval(doStuff, 1000);
// On shutdown or cleanup
clearInterval(intervalId);
For long-running servers, clean up inside lifecycle events:
server.on('close', () => clearInterval(intervalId));
How to Detect and Debug Memory Leaks
1. Using process.memoryUsage()
Quick way to track memory usage:
console.log(process.memoryUsage());
rss
: Total memory allocated for the processheapUsed
: Actual memory used by JS objectsheapTotal
: Total allocated heap
2. Using Chrome DevTools + Heap Snapshots
Run your app with:
node --inspect server.js
Open Chrome →
chrome://inspect
Take snapshots over time and compare retained objects
3. Use clinic.js
, heapdump
, or memwatch-next
These tools can help visualize memory growth and locate leaks:
heapdump
: Generates heap snapshots from running processesmemwatch-next
: Emits events on memory leaks
How to Prevent Memory Leaks in Node.js
Use this checklist to stay clean:
✅ Avoid storing large data in global or static variables
✅ Remove event listeners when done:
emitter.removeListener()
✅ Clear timeouts and intervals in
onClose
,onExit
, orfinally
blocks✅ Use
WeakMap
orWeakSet
for objects that should not prevent GC✅ Monitor memory regularly (especially for long-running services)
Node.js Isn't the Problem — It's the Patterns
Node.js and V8 do a great job at memory management — when we write code that plays nice with GC.
If you’re:
Holding on to data forever
Not cleaning up listeners
Growing caches unbounded
…you’re unintentionally preventing the GC from doing its job. The goal isn’t to fight the GC, but to write code that makes garbage collection easy.
Conclusion: Own Your Memory
Memory leaks are a natural challenge in long-running Node.js applications — but they’re entirely avoidable.
Takeaways:
Understand how V8's GC works
Know where leaks come from
Use the right tools to monitor and fix them
Start by adding process.memoryUsage()
to your logs. Take snapshots. Watch for growth. And clean up what you don’t need.
The best memory leak is the one you prevent from ever happening.
📣 Want More?
Up next: we’ll explore real-world memory debugging with clinic.js
and how to use heap snapshots
to find hidden object references.
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Written by

Faiz Ahmed Farooqui
Faiz Ahmed Farooqui
Principal Technical Consultant at GeekyAnts. Bootstrapping our own Data Centre services. I lead the development and management of innovative software products and frameworks at GeekyAnts, leveraging a wide range of technologies including OpenStack, Postgres, MySQL, GraphQL, Docker, Redis, API Gateway, Dapr, NodeJS, NextJS, and Laravel (PHP). With over 9 years of hands-on experience, I specialize in agile software development, CI/CD implementation, security, scaling, design, architecture, and cloud infrastructure. My expertise extends to Metal as a Service (MaaS), Unattended OS Installation, OpenStack Cloud, Data Centre Automation & Management, and proficiency in utilizing tools like OpenNebula, Firecracker, FirecrackerContainerD, Qemu, and OpenVSwitch. I guide and mentor a team of engineers, ensuring we meet our goals while fostering strong relationships with internal and external stakeholders. I contribute to various open-source projects on GitHub and share industry and technology insights on my blog at blog.faizahmed.in. I hold an Engineer's Degree in Computer Science and Engineering from Raj Kumar Goel Engineering College and have multiple relevant certifications showcased on my LinkedIn skill badges.