# Step 1 — Understand What a Memory Leak Is

• Memory Leak → when your app keeps using memory without releasing it

• Signs of a memory leak:

  • Node.js process grows in memory over time

  • App slows down or crashes

  • Logs show “heap out of memory”

• Common causes:

  • Global variables holding large objects

  • Caches without limits

  • Unclosed database connections or event listeners

  • Long-lived timers (setInterval) or callbacks

---

## Step 2 — Monitor Memory Usage

• Use terminal commands:

ps aux | grep node
top
htop

• Check the RSS / memory usage of Node.js process

• Observe over time to see if memory grows steadily

---

## Step 3 — Use Node.js Built-In Tools

• Start your app with:

node --inspect app.js

• Open Chrome → chrome://inspect → Remote Target → Inspect

• Go to Memory tab → take snapshots

• Look for objects that keep increasing

---

## Step 4 — Use Heap Snapshots

• Take multiple heap snapshots at intervals:

global.gc(); // force garbage collection

• Compare snapshots to find objects that are not released

• Use --expose-gc when starting Node.js:

node --expose-gc app.js

• Helps detect what’s causing memory to grow

---

## Step 5 — Identify Common Leak Sources

1. Global Variables

global.leak = []; // grows infinitely

• Use local scope or clean arrays regularly

2. Unclosed Database Connections

// Wrong: not closing connection
db.query('SELECT * FROM users');

• Always close connections or use connection pools

3. Timers / Intervals

setInterval(() => { cache.push(data); }, 1000);

• Clear intervals when not needed:

const interval = setInterval(...);
clearInterval(interval);

4. Event Listeners

emitter.on('data', handler); // keep adding

• Remove unused listeners: emitter.removeListener('data', handler)

---

## Step 6 — Limit Caches and Large Arrays

• Keep caches limited:

const cache = new Map();

function addToCache(key, value) {
  if (cache.size > 100) { // limit size
    const firstKey = cache.keys().next().value;
    cache.delete(firstKey);
  }
  cache.set(key, value);
}

• Prevent unbounded memory growth

---

## Step 7 — Use Profiling Tools

• Clinic.js (recommended for beginners)

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

• Shows memory and CPU usage

• Detects potential leaks

• Other tools:

  • Node.js Inspector

  • Chrome DevTools → Memory profiling

  • heapdump package for offline analysis

---

## Step 8 — Restart Strategy (Temporary Fix)

• Use PM2 to auto-restart if memory grows:

pm2 start app.js --max-memory-restart 200M

• Good for production until leak is fixed

• Not a permanent solution

---

## Step 9 — Beginner-Friendly Checklist

---

## Step 10 — Conclusion

Memory leaks in Node.js can seem intimidating, but beginners can tackle them by:

• Monitoring memory usage over time

• Using heap snapshots and profiling tools

• Fixing common leak sources: globals, database connections, timers, event listeners, caches

• Using PM2 or similar tools to manage memory in production

Following these steps ensures your Node.js server runs efficiently and avoids crashes due to memory leaks.