Debug: Node.js heap out of memory

Node.js crashes with 'JavaScript heap out of memory' during build, test, or runtime.

Diagnose and fix heap memory issues:

# 1. Increase heap size (immediate fix)
node --max-old-space-size=4096 app.js  # 4GB

# For npm scripts
NODE_OPTIONS='--max-old-space-size=4096' npm run build

# 2. Profile memory usage
node --inspect app.js
# Open chrome://inspect -> Memory tab -> Take heap snapshot

# 3. Programmatic monitoring
const v8 = require('v8');
setInterval(() => {
  const stats = v8.getHeapStatistics();
  const used = Math.round(stats.used_heap_size / 1024 / 1024);
  const total = Math.round(stats.total_heap_size / 1024 / 1024);
  console.log(`Heap: ${used}MB / ${total}MB`);
}, 10000);

Common causes:

• Webpack/Vite builds: Large source maps or many modules

- Fix: Set NODE_OPTIONS=--max-old-space-size=4096
- Fix: Use devtool: 'eval-source-map' for dev

• Large JSON parsing: JSON.parse() on huge files

- Fix: Use streaming JSON parser (JSONStream, stream-json)

• Accumulating data: Arrays/objects that grow without bounds

- Fix: Process in batches, stream, or set size limits

• TypeScript compilation: Large projects

- Fix: Use project references, incremental builds

• Jest tests: Leaking between test files

- Fix: --maxWorkers=2, --forceExit, investigate leaking globals

Node.js default heap is ~1.5GB (v8 default). Build tools, large datasets, and memory leaks can easily exceed this.

Node.js applications hitting memory limits