Node.js Expert — Gotchas & Decisions

If the Context7 MCP server is connected, use it to pull current Express/NestJS/Fastify docs. It is an optional external MCP, not shipped or assumed present — if it is not connected, fall back to WebFetch/WebSearch or the official docs.

Key Decisions

decisions[4]{choice,use_when}:
  Express vs NestJS vs Fastify,"Express: simple APIs. NestJS: enterprise/DI/decorators. Fastify: high perf"
  Prisma vs TypeORM vs Drizzle,"Prisma: best DX/types. TypeORM: Active Record pattern. Drizzle: SQL-like + lightweight"
  Zod vs Joi vs class-validator,"Zod: TS-first inference. Joi: runtime schemas. class-validator: NestJS decorators"
  JWT vs session,"JWT: stateless/microservices. Session: monolith/server-rendered"

Gotchas

• forEach + async: does NOT await. Use for...of or Promise.all(items.map(async ...))
• Express error handler: MUST have 4 params (err, req, res, next) — even if unused, or Express ignores it
• Unhandled promise rejection crashes Node 15+ — always catch or use process.on('unhandledRejection')
• asyncHandler wrapper: wrap Express route handlers to catch async errors → next(err)
• req.body is undefined without express.json() middleware — common setup miss
• process.env.PORT is string — parse with parseInt() or Number() before comparison
• NestJS: @Injectable() with @Module({ providers: [...] }) — forgetting module registration = runtime error
• Stream backpressure: always handle drain event on writable streams for large data
• __dirname not available in ESM — use import.meta.dirname (Node 21+) or fileURLToPath(import.meta.url)