nodejs-backend

Node.js Backend

Verify before implementing: For framework-specific APIs (Express 5, Fastify 5, Node.js 22+ built-ins), look up current, version-matched official docs before writing code. Prefer Context7 (query-docs) when available. Otherwise use available web tools to read the framework's official documentation, or the Node.js API docs for Node.js built-ins. Training data may lag current releases.

Working rules

• Validate request and third-party data before use; keep response serialization and error envelopes explicit.
• Preserve caller-visible contracts and authorization when adding resilience or fallbacks.
• Bound concurrency, set timeouts, and avoid blocking production request paths.
• Verify actual resource identity before parsing or caching a reused client's result.
• Exercise operational telemetry and failure paths, not successful return codes alone.

Architecture

src/
├── routes/          # HTTP: parse request, call service, format response
├── middleware/       # Auth, validation, rate limiting, logging
├── services/        # Business logic (no HTTP types)
├── repositories/    # Data access only (queries, ORM)
├── config/          # Env, DB pool, constants
└── types/           # Shared TypeScript interfaces

• Routes never contain business logic
• Services never import Request/Response
• Repositories never throw HTTP errors
• Dependencies point inward only (Clean Architecture rule): routes -> services -> repositories. Never the reverse.
• For scripts/prototypes: single file is fine; ask "will this grow?"

TypeScript Rules

• Use import type { } for type-only imports; eliminates runtime overhead
• Prefer interface for object shapes (2-5x faster type resolution than intersections)
• Prefer unknown over any; forces explicit narrowing
• Use z.infer<typeof Schema> as single source of truth; never duplicate types and schemas
• Minimize as assertions; use type guards instead
• Add explicit return types to exported functions (faster declaration emit)
• Untyped package? declare module 'pkg' { const v: unknown; export default v; } in types/ambient.d.ts