hardLow-Level Design

What are memory leaks in Node.js and how do you detect them?

Q: What are memory leaks in Node.js and how do you detect them?

**TL;DR.** A **memory leak** is memory the GC can't reclaim because something still **references** it. Common causes: ever-growing **global** state/caches, **un-removed event listeners**, lingering **closures/timers**, and unbounded data structures. Detect with process.memoryUsage() trends and **heap snapshot diffs**; the tell-tale is heap that grows and never returns after GC. time → heap keeps climbing **

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Explain common sources of memory leaks in long-running Node.js processes and how to troubleshoot them.

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A classic listener leak and its fix

// ❌ leak: a new listener every request, never removed
app.get('/x', (req, res) => {
  emitter.on('tick', () => res.write('.'));   // retains res forever
});

// ✅ remove it when done
app.get('/x', (req, res) => {
  const onTick = () => res.write('.');
  emitter.on('tick', onTick);
  res.on('close', () => emitter.off('tick', onTick));
});

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