Exception mapping interceptor in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the necessary decorator for creating an interceptor.

NestJS

import { [1] } from '@nestjs/common';

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AInjectable

BController

CModule

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Controller instead of @Injectable

Forgetting to import any decorator

Using @Module or @Service which are unrelated here

The @Injectable decorator is required to define an interceptor class in NestJS.

2fill in blank

medium

Complete the code to implement the intercept method signature in the interceptor class.

NestJS

intercept(context: ExecutionContext, next: [1]): Observable<any> {

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ACallHandler

BRequest

CResponse

DHttpException

Attempts:

3 left

💡 Hint

Common Mistakes

Using Request or Response instead of CallHandler

Confusing with exception classes

The intercept method receives a CallHandler as the second argument to handle the request flow.

3fill in blank

hard

Fix the error in the pipe method to catch exceptions and map them.

NestJS

return next.handle().pipe(catchError(error => throwError(() => new [1](error.message, 500))));

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AObservable

BError

CHttpException

DInterceptor

Attempts:

3 left

💡 Hint

Common Mistakes

Throwing generic Error instead of HttpException

Using Observable or Interceptor which are not error classes

To map exceptions properly, you throw a new HttpException with the error message.

4fill in blank

hard

Fill both blanks to create a custom exception mapping interceptor class.

NestJS

import { [1], NestInterceptor, ExecutionContext, CallHandler, HttpException } from '@nestjs/common';
import { Observable, throwError } from 'rxjs';
import { catchError } from 'rxjs/operators';

@[2]()
export class ExceptionMappingInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    return next.handle().pipe(
      catchError(error => {
        return throwError(() => new HttpException(error.message, error.status || 500));
      }),
    );
  }
}

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AInjectable

BController

CModule

DService

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Controller or @Module decorators

Forgetting to import Injectable

The class must be decorated with @Injectable and import it to be recognized as an interceptor.

5fill in blank

hard

Fill all three blanks to complete the interceptor that maps exceptions with status and message.

NestJS

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

@Injectable()
export class ExceptionMappingInterceptor implements NestInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<any> {
    return next.handle().pipe(
      catchError(error => {
        const status = error?.[1] || 500;
        const message = error?.[2] || 'Internal Server Error';
        return throwError(() => new [3](message, status));
      }),
    );
  }
}

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Astatus

Bmessage

CHttpException

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong property names like 'error' instead of 'status' or 'message'

Throwing generic Error instead of HttpException

The interceptor extracts status and message from the error object and throws a new HttpException with those values.