Express.js REST API

To separate business logic in an Express.js REST API, move HTTP concerns into controllers, pure rules into services, and persistence into models, keeping route handlers clean and preventing tightly coupled code.

The best way to structure an Express.js REST API is organizing code into src/routes, src/controllers, src/services, src/models, and src/middleware to prevent mixed HTTP, business, and persistence logic.

Centralized error handling in an Express.js REST API is implemented by placing cross-cutting concerns in src/middleware and using AppError-based responses to enforce consistent error handling across the codebase.

Yes, you can refactor existing Express.js endpoints by migrating mixed logic into a layered design with storage-agnostic services and dependency injection, ensuring safe refactoring without coupling req/res objects.

Express.js service layers couple to req and res because of mixed logic; refactoring into storage-agnostic services free of HTTP coupling via dependency injection ensures pure business rules and safe changes.

Yes, this layered architecture standardizes Express.js REST API structure for both implementing new endpoints and refactoring existing APIs, enforcing consistent middleware and separation rules across any codebase.