Find and Fix Memory Leaks

Advanced20 minTrending

Detect memory leaks in Node.js applications using heap snapshots, process.memoryUsage(), and diagnostic tools.

Prerequisites

-Node.js installed
-Chrome browser for heap analysis

Steps

Monitor memory usage over time

Log heap usage at intervals to identify a growing memory trend that indicates a leak.

$ node -e " setInterval(() => { const mem = process.memoryUsage(); console.log(JSON.stringify({ heapUsed: Math.round(mem.heapUsed / 1024 / 1024) + 'MB', heapTotal: Math.round(mem.heapTotal / 1024 / 1024) + 'MB', rss: Math.round(mem.rss / 1024 / 1024) + 'MB', external: Math.round(mem.external / 1024 / 1024) + 'MB' })); }, 5000); "

A steadily growing heapUsed value over time is the clearest indicator of a memory leak.

Take heap snapshots with --inspect

Start the app with inspect and use Chrome DevTools Memory tab to take snapshots at different points.

$ node --inspect --max-old-space-size=512 app.js

Take a snapshot after startup, then again after load. Compare the two to find objects that should have been garbage collected.

Generate heap snapshots programmatically

Use v8.writeHeapSnapshot() to create heap dumps from code or signal handlers for automated analysis.

$ node -e " const v8 = require('v8'); const path = require('path'); // Write snapshot on SIGUSR2 process.on('SIGUSR2', () => { const file = v8.writeHeapSnapshot(); console.log('Heap snapshot written to:', file); }); console.log('PID:', process.pid, '- Send SIGUSR2 to take snapshot'); setInterval(() => {}, 1000); "

Heap snapshots pause the event loop and can be large (hundreds of MB). Do not take them frequently in production.

Compare snapshots in Chrome DevTools

Load two snapshots in the DevTools Memory panel and use the Comparison view to find leaked objects.

$ # In Chrome DevTools Memory tab: # 1. Load first snapshot (baseline) # 2. Load second snapshot (after suspected leak) # 3. Select 'Comparison' view in the second snapshot # 4. Sort by 'Alloc. Size' descending to find growing objects

Use clinic.js for automated analysis

Install and run clinic.js to automatically detect memory issues with visual flame charts.

$ npm install -g clinic clinic heapprofile -- node app.js

clinic heapprofile generates an interactive HTML report showing allocation patterns and potential leak sources.

Check for common leak patterns

Review code for the most frequent causes of Node.js memory leaks.

$ # Common leak patterns to search for: grep -rn 'addEventListener\|setInterval\|global\.' src/ --include='*.ts' --include='*.js' | head -20

The top causes are: unremoved event listeners, growing global caches without eviction, uncleared intervals, and closures retaining large objects.

Full Script

full-script.sh

#!/bin/bash
set -euo pipefail

# Node.js Memory Leak Detection Script

APP_FILE="${1:-app.js}"
INTERVAL="${2:-30}"

echo "==> Starting memory monitoring for ${APP_FILE}..."
echo "    Sampling every ${INTERVAL} seconds"
echo ""

# Create monitoring wrapper
cat > /tmp/mem-monitor.js <<'MONITOR'
const v8 = require('v8');
const path = require('path');

// Memory logging
const baseline = process.memoryUsage().heapUsed;
let samples = [];

setInterval(() => {
  const mem = process.memoryUsage();
  const heapMB = Math.round(mem.heapUsed / 1024 / 1024);
  const rssMB = Math.round(mem.rss / 1024 / 1024);
  const growthMB = Math.round((mem.heapUsed - baseline) / 1024 / 1024);

  samples.push(heapMB);

  const trend = samples.length > 5
    ? (samples[samples.length - 1] > samples[0] ? 'GROWING' : 'STABLE')
    : 'SAMPLING';

  console.log(`[MEM] heap=${heapMB}MB rss=${rssMB}MB growth=${growthMB >= 0 ? '+' : ''}${growthMB}MB trend=${trend}`);

  if (trend === 'GROWING' && samples.length > 10) {
    console.log('[MEM] WARNING: Memory appears to be leaking. Consider taking a heap snapshot.');
  }
}, parseInt(process.env.MONITOR_INTERVAL || '30') * 1000);

// Snapshot on SIGUSR2
process.on('SIGUSR2', () => {
  const file = v8.writeHeapSnapshot();
  console.log('[MEM] Heap snapshot written to:', file);
});

console.log('[MEM] Memory monitor active. PID:', process.pid);
console.log('[MEM] Send SIGUSR2 to take heap snapshot');
MONITOR

echo "==> Running with memory monitor..."
MONITOR_INTERVAL=${INTERVAL} node --inspect --max-old-space-size=512 -r /tmp/mem-monitor.js "${APP_FILE}"

FAQ

Discussion

Loading comments...

#!/bin/bash set -euo pipefail # Node.js Memory Leak Detection Script APP_FILE="${1:-app.js}" INTERVAL="${2:-30}" echo "==> Starting memory monitoring for ${APP_FILE}..." echo " Sampling every ${INTERVAL} seconds" echo "" # Create monitoring wrapper cat > /tmp/mem-monitor.js <<'MONITOR' const v8 = require('v8'); const path = require('path'); // Memory logging const baseline = process.memoryUsage().heapUsed; let samples = []; setInterval(() => { const mem = process.memoryUsage(); const heapMB = Math.round(mem.heapUsed / 1024 / 1024); const rssMB = Math.round(mem.rss / 1024 / 1024); const growthMB = Math.round((mem.heapUsed - baseline) / 1024 / 1024); samples.push(heapMB); const trend = samples.length > 5 ? (samples[samples.length - 1] > samples[0] ? 'GROWING' : 'STABLE') : 'SAMPLING'; console.log(`[MEM] heap=${heapMB}MB rss=${rssMB}MB growth=${growthMB >= 0 ? '+' : ''}${growthMB}MB trend=${trend}`); if (trend === 'GROWING' && samples.length > 10) { console.log('[MEM] WARNING: Memory appears to be leaking. Consider taking a heap snapshot.'); } }, parseInt(process.env.MONITOR_INTERVAL || '30') * 1000); // Snapshot on SIGUSR2 process.on('SIGUSR2', () => { const file = v8.writeHeapSnapshot(); console.log('[MEM] Heap snapshot written to:', file); }); console.log('[MEM] Memory monitor active. PID:', process.pid); console.log('[MEM] Send SIGUSR2 to take heap snapshot'); MONITOR echo "==> Running with memory monitor..." MONITOR_INTERVAL=${INTERVAL} node --inspect --max-old-space-size=512 -r /tmp/mem-monitor.js "${APP_FILE}"