# Nodejs Expert > Node.js gotchas and decision criteria. Covers async pitfalls, Express/NestJS patterns, and common mistakes. Use when this capability is needed. - Skill: `tomevault-io/nodejs-expert-3` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/nodejs-expert-3` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/nodejs-expert-3/raw - Safety review: pending - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/nodejs-expert-3 --- > **AI-consumed reference.** Optimized for Claude to read during execution. > Human-readable explanation: see [docs/architecture/HIERARCHICAL_PLANNING.md](../../../docs/architecture/HIERARCHICAL_PLANNING.md) > or [docs/getting-started/](../../../docs/getting-started/) depending on topic. # Node.js Expert — Gotchas & Decisions Use Context7 for Express/NestJS/Fastify docs. ## Key Decisions ```toon 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)` --- > Source: [nguyenthienthanh/aura-frog](https://github.com/nguyenthienthanh/aura-frog) — distributed by [TomeVault](https://tomevault.io).