NodeJS

Quick Reference

| Topic | File | |-------|------| | Callbacks, Promises, async/await, event loop | async.md | | CommonJS vs ESM, require vs import | modules.md | | Error handling, uncaught exceptions | errors.md | | Readable, Writable, Transform, backpressure | streams.md | | Memory leaks, event loop blocking, profiling | performance.md | | Input validation, dependencies, env vars | security.md | | Jest, Mocha, mocking, integration tests | testing.md | | npm, package.json, lockfiles, publishing | packages.md |

Critical Traps

• fs.readFileSync blocks entire server — use fs.promises.readFile
• Unhandled rejection crashes Node 15+ — always .catch() or try/catch
• process.env values are strings — "3000" not 3000, parseInt needed
• JSON.parse throws on invalid — wrap in try/catch
• require() cached — same object, mutations visible everywhere
• Circular deps return incomplete export — restructure to avoid
• Event listeners accumulate — removeListener or once()
• async always returns Promise — even for plain return
• pipeline() over .pipe() — handles errors and cleanup
• No __dirname in ESM — use fileURLToPath(import.meta.url)
• Buffer.from(string) — encoding matters, default UTF-8