backend-patterns

Repository and service layer patterns separate data access from business logic in Node.js APIs. The repository handles database queries, the service layer contains business rules, and controllers manage HTTP requests. This structure improves testability, maintainability, and scalability as your API grows.

Middleware composition in Express chains validation, authentication, and error handling functions before route handlers execute. Order matters: validation middleware runs first, then business logic, then centralized error handlers catch exceptions. This pattern prevents invalid requests from reaching your database and standardizes error responses.

TypeScript with Node.js and Express enables type-safe backend development and catches errors at compile time rather than runtime. Combined with repository and service layer patterns, TypeScript reduces bugs in complex APIs and makes refactoring safer as systems scale.

Caching patterns store frequently accessed data in memory or external caches to reduce database load and latency. In Node.js services, caching typically sits between the service layer and repository, invalidating selectively when data changes. This approach significantly improves API response times under load.

Testing TypeScript backends involves unit tests for service layer logic, integration tests for repository and middleware behavior, and end-to-end tests for API routes. Separating concerns via repository and service patterns makes each layer independently testable and reduces test complexity.

Refactoring monoliths into modular services reduces coupling and enables independent scaling. Clear strategies involve extracting repository and service layers first, then migrating routes into separate modules with minimal disruption. TypeScript type definitions help ensure compatibility across new boundaries.