nodejs-backend

A maintainable Node.js backend architecture separates pure business logic in a core directory from side effects like HTTP and database access in an infra directory to reduce coupling and improve testability.

The best way to handle API input validation in Express is using Zod to parse and validate request inputs at the route handler level before passing data to your core business logic.

The repository pattern for Node.js database transactions abstracts data access behind repository interfaces, allowing multi-step operations like transfers to execute reliably while keeping persistence logic decoupled from core logic.

You standardize error handling in an Express or Fastify API by throwing domain errors with attached status codes and routing them through a global error middleware to ensure consistent failure responses.

Yes, dependency injection at the composition root is required to build a production-ready Node.js API, ensuring route handlers receive services without tight coupling to specific infrastructure implementations.

Yes, you use Supertest for integration testing to verify API endpoints, while unit tests target the isolated core services, ensuring both HTTP routes and business logic remain reliable.