Questions
3 of 6
1What is an interceptor in NestJS and what can it do that guards and middleware cannot?
2What is the difference between tap(), map(), and catchError() in an interceptor's RxJS pipeline?
3How do you use an interceptor to transform every response into a standard envelope format in NestJS?
4How do you implement a caching interceptor that short-circuits the handler in NestJS?
5How do interceptors handle errors vs exception filters in NestJS — what is the division of responsibility?
6How would you implement a request-scoped audit log interceptor that captures both the request and response body in NestJS?
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How do you use an interceptor to transform every response into a standard envelope format in NestJS?

Implement NestInterceptor with a generic type, use map() in the RxJS pipeline to wrap every handler return value in a standard object. Register globally via APP_INTERCEPTOR or app.useGlobalInterceptors() so every endpoint returns the same shape.

Response transform interceptor
Global registration options:
  1. 1

    app.useGlobalInterceptors(new TransformInterceptor()) — no DI support.

  2. 2

    { provide: APP_INTERCEPTOR, useClass: TransformInterceptor } — full DI support, preferred.

  3. 3

    The map() operator transforms every emitted value from the handler's observable.

  4. 4

    null and undefined handler returns are also passed through map() — handle them if needed.