Timeout interceptor in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Timeout Interceptor in NestJS?

A Timeout Interceptor in NestJS is a piece of code that automatically stops a request if it takes longer than a set time. It helps keep the app responsive by avoiding long waits.

intermediate

How do you apply a Timeout Interceptor globally in NestJS?

You apply it globally by using app.useGlobalInterceptors(new TimeoutInterceptor()) in the main bootstrap file. This makes all requests use the timeout rule.

intermediate

Which RxJS operator is commonly used inside a Timeout Interceptor to enforce the timeout?

The timeout operator from RxJS is used. It throws an error if the observable does not emit a value within the specified time.

beginner

What happens if a request exceeds the timeout set by the Timeout Interceptor?

The interceptor throws a TimeoutError, which usually results in a 408 Request Timeout response sent back to the client.

advanced

Show a simple example of a Timeout Interceptor class in NestJS.

import { Injectable, NestInterceptor, ExecutionContext, CallHandler, RequestTimeoutException } from '@nestjs/common';
import { Observable, throwError, TimeoutError } from 'rxjs';
import { timeout, catchError } from 'rxjs/operators';

@Injectable()
export class TimeoutInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    return next.handle().pipe(
      timeout(5000), // 5 seconds timeout
      catchError(err => {
        if (err instanceof TimeoutError) {
          return throwError(() => new RequestTimeoutException());
        }
        return throwError(() => err);
      }),
    );
  }
}

What is the main purpose of a Timeout Interceptor in NestJS?

A To authenticate users

B To stop requests that take too long

C To cache responses

D To log all incoming requests

Timeout Interceptors stop requests that exceed a set time to keep the app responsive.

Which RxJS operator is used to enforce a timeout in a NestJS interceptor?

A mergeMap

B map

C filter

D timeout

The timeout operator throws an error if the observable takes too long.

What exception is typically thrown when a timeout occurs in NestJS?

A BadRequestException

B UnauthorizedException

C RequestTimeoutException

D NotFoundException

RequestTimeoutException signals that the request took too long and was stopped.

How do you apply a Timeout Interceptor to all routes in a NestJS app?

A Call app.useGlobalInterceptors() with the interceptor

B Use @Timeout() decorator on each controller

C Add timeout in main.ts without interceptor

D Set timeout in the database config

Using app.useGlobalInterceptors applies the interceptor app-wide.

If a Timeout Interceptor is set to 3 seconds, what happens if a request takes 5 seconds?

A The request is canceled and a timeout error is returned

B The request completes normally

C The server crashes

D The request is retried automatically

The interceptor cancels the request and returns a timeout error.

Explain how a Timeout Interceptor works in NestJS and why it is useful.

Think about how to handle slow requests in a web app.

Describe how to create and apply a Timeout Interceptor globally in a NestJS application.

Focus on the class structure and global setup.