How to handle memory leaks in Node.js
Łukasz Holeczek
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Memory leaks in Node.js applications cause gradual performance degradation and eventual crashes, making them critical to identify and resolve in production environments. With over 12 years of Node.js experience since 2014 and as the creator of CoreUI, I’ve debugged memory leaks in numerous backend systems serving millions of requests. Common causes include unclosed database connections, event listeners that aren’t removed, and global variable accumulation. The solution involves using Chrome DevTools heap snapshots to identify leaks and implementing proper cleanup patterns.
Use heap snapshots to identify memory leaks and implement proper cleanup for event listeners and resources.
// Common memory leak: Event listeners not removed
class UserService {
constructor() {
this.emitter = new EventEmitter()
// BAD: Listener never removed
this.emitter.on('user:created', this.handleUserCreated)
}
handleUserCreated(user) {
console.log('User created:', user)
}
// GOOD: Cleanup method
cleanup() {
this.emitter.removeListener('user:created', this.handleUserCreated)
}
}
// Common memory leak: Global references
const cache = {} // BAD: Grows indefinitely
// GOOD: Use Map with size limit
class LRUCache {
constructor(maxSize = 100) {
this.cache = new Map()
this.maxSize = maxSize
}
set(key, value) {
if (this.cache.size >= this.maxSize) {
const firstKey = this.cache.keys().next().value
this.cache.delete(firstKey)
}
this.cache.set(key, value)
}
}
// Always close connections
const connection = await db.connect()
try {
await connection.query('SELECT * FROM users')
} finally {
await connection.close() // Ensure cleanup
}
Best Practice Note
Monitor memory usage with process.memoryUsage() and set up alerts when heap usage exceeds thresholds. Use --inspect flag and Chrome DevTools to take heap snapshots before and after operations to identify growing objects. Tools like clinic.js and node-memwatch automate leak detection. This is the same approach we use for CoreUI backend services—implementing strict resource cleanup, using WeakMap for caches, and continuously monitoring production memory metrics.
