Interceptor interface in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the Interceptor interface in NestJS?

The Interceptor interface allows you to add extra logic before or after method execution, transform the result, or handle errors in a centralized way.

beginner

Which method must be implemented when creating a class that uses the Interceptor interface?

You must implement the intercept(context: ExecutionContext, next: CallHandler): Observable<any> method.

intermediate

What does the next.handle() call inside the intercept method do?

It passes control to the next handler in the request pipeline and returns an Observable of the response.

intermediate

How can you modify the response data inside an interceptor?

By using RxJS operators like map on the Observable returned by next.handle() to transform the data before sending it to the client.

beginner

Name two common use cases for interceptors in NestJS.

Logging request/response data and transforming response formats are common uses of interceptors.

What does the Interceptor interface in NestJS primarily allow you to do?

A Handle HTTP routing

B Define database schemas

C Manage user authentication

D Add logic before and after method execution

Interceptors let you add extra logic before or after method calls, such as logging or transforming data.

Which method signature is required by the Interceptor interface?

A intercept(context: ExecutionContext, next: CallHandler)

B handle(request: Request, response: Response)

C execute(context: Context)

D process(data: any)

The intercept method with parameters context and next is required to implement the Interceptor interface.

Inside the intercept method, what does calling next.handle() return?

A A Promise of the response

B An Observable of the response

C A callback function

D A synchronous value

next.handle() returns an Observable that emits the response data.

Which RxJS operator is commonly used inside interceptors to modify response data?

A map

B concat

C reduce

D filter

The map operator transforms the emitted data from the Observable.

Which of these is NOT a typical use case for NestJS interceptors?

A Logging requests

B Transforming responses

C Handling database migrations

D Measuring execution time

Database migrations are handled separately, not by interceptors.

Explain how the Interceptor interface works in NestJS and what you can do inside the intercept method.

Think about how you can control the flow of a request and response.

Describe two practical examples where you might use an interceptor in a NestJS application.

Consider common tasks that happen around method calls.