NestJS

NestJS interviews test opinionated structure: modules, controllers, providers, dependency injection, guards, pipes, interceptors, filters, CQRS, microservices, and the testing module.

Subtopics: modules, controllers, providers, DI, guards, interceptors, pipes, filters, CQRS, microservices, and testing module.

On interviews: trace a request through guards and pipes to a thin controller, explain provider scopes, and show how TestingModule enables overrides.

Common pitfalls: fat controllers, guards that perform authorization without resource context, request-scoped providers everywhere, and CQRS without a real scaling need.

The trade-off is balancing simplicity, performance, safety, and operability — name which axis you optimized and what cost you accepted.

Checklist:

• Organize features with explicit module boundaries.
• Use guards/pipes/filters at the right layer.
• Inject dependencies for testable services.
• Know when HTTP vs microservice transport fits.