How to detect and fix memory leaks in Node.js?

What You'll Learn

Common causes of memory leaks
Detection tools
How to fix them

Common Causes

Global variables
Closures retaining references
Event listeners not removed
Growing arrays/objects
Timers not cleared

Detection

code.jsJavaScript

// Monitor memory usage
setInterval(() => {
  const used = process.memoryUsage();
  console.log({
    heapTotal: Math.round(used.heapTotal / 1024 / 1024) + 'MB',
    heapUsed: Math.round(used.heapUsed / 1024 / 1024) + 'MB',
    external: Math.round(used.external / 1024 / 1024) + 'MB'
  });
}, 5000);

Using Heap Snapshots

$ terminalBash

node --inspect app.js

Open Chrome DevTools and take heap snapshots.

Common Fixes

code.jsJavaScript

// ❌ Memory leak: event listeners pile up
socket.on('data', handleData);

// ✅ Fix: remove listener when done
socket.on('data', handleData);
socket.on('close', () => {
  socket.removeListener('data', handleData);
});

// ❌ Memory leak: growing array
const cache = [];
function addToCache(item) {
  cache.push(item);
}

// ✅ Fix: limit size
function addToCache(item) {
  if (cache.length >= 1000) cache.shift();
  cache.push(item);
}

// ❌ Memory leak: timer not cleared
const interval = setInterval(doSomething, 1000);

// ✅ Fix: clear when done
clearInterval(interval);

Using clinic.js

$ terminalBash

npm install -g clinic
clinic doctor -- node app.js