Building Production-Grade APIs with NestJS

Why NestJS?

Express gives you full control. NestJS gives you a structure. For solo developers and small teams, structure wins. NestJS enforces separation of concerns through its module system, which means your codebase stays navigable even as it grows.

Module Structure

Every feature module follows the same pattern: controller → service → repository. The controller handles HTTP. The service handles business logic. The repository handles data access. Nothing bleeds between layers.

The Global Response Interceptor

Every API response should have the same shape. Create a TransformInterceptor that wraps every response in { success, data, message, meta }. Register it globally in main.ts. Now your frontend never has to guess the response shape.

Guards vs Middleware vs Interceptors

• Guard: Can this request proceed? (auth, roles)
• Interceptor: Transform what goes in or out (logging, response shape)
• Middleware: Cross-cutting concerns before the route handler (request ID, logger)

Most developers overuse middleware when guards or interceptors are the right tool.