Debugging Memory Leaks in Node.js Applications

Introduction

Memory leaks can cause performance degradation and crashes. This tutorial covers techniques to detect, analyze, and fix memory leaks in Node.js.

Prerequisites

• Node.js >=14

Step 1: Enable Heap Snapshots

Run Node.js with the inspector:

node --inspect-brk app.js

Open Chrome DevTools > Memory tab > click Take heap snapshot.

Step 2: Analyze Heap Snapshots

• Compare snapshots over time to find growing object counts.
• Look for detached DOM trees or retained closures.

Step 3: Use Heapdump for On-Demand Snaps

Install:

npm install heapdump

In code:

const heapdump = require("heapdump");

process.on("SIGUSR2", () => {
  const filename = `./${Date.now()}.heapsnapshot`;
  heapdump.writeSnapshot(filename, err => {
    if (err) console.error(err);
    else console.log(`Heap snapshot written to ${filename}`);
  });
});

Trigger snapshot:

kill -SIGUSR2 <pid>

Step 4: Monitor Real-Time Memory Usage

Use --trace-gc flag:

node --trace-gc app.js

Logs show GC activity and memory reclaimed.

Step 5: Common Leak Patterns

• Unbounded caches
• Forgotten timers or intervals
• Global variables holding references

Step 6: Fixing Leaks

• Clear timers (clearInterval)
• Limit cache size or use LRU
• Avoid retaining large structures in closures

Summary

Regular memory profiling and heap snapshot analysis help identify leaks early, ensuring stable and performant Node.js applications.