NodeJS

Write reliable Node.js avoiding event loop blocking, async pitfalls, ESM gotchas, and memory leaks.

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