Exception filters in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a basic exception filter class in NestJS.

NestJS

import { ExceptionFilter, Catch, ArgumentsHost } from '@nestjs/common';

@Catch()
export class AllExceptionsFilter implements [1] {
  catch(exception: any, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    response.status(500).json({
      statusCode: 500,
      message: 'Internal server error',
    });
  }
}

Drag options to blanks, or click blank then click option'

AController

BExceptionFilter

CHttpException

DMiddleware

Attempts:

3 left

💡 Hint

Common Mistakes

Using HttpException instead of ExceptionFilter as the implemented interface.

Not implementing any interface.

Using Controller or Middleware which are unrelated here.

The class must implement the ExceptionFilter interface to be a valid exception filter in NestJS.

2fill in blank

medium

Complete the code to catch only HTTP exceptions in the filter.

NestJS

import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from '@nestjs/common';

@Catch([1])
export class HttpExceptionFilter implements ExceptionFilter {
  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const status = exception.getStatus();
    response.status(status).json({
      statusCode: status,
      message: exception.message,
    });
  }
}

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AExceptionFilter

BError

CHttpException

DAllExceptionsFilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using Error which is too general.

Using ExceptionFilter which is an interface, not an exception class.

Using a custom filter class name instead of an exception class.

The @Catch() decorator takes the exception type to catch. To catch HTTP exceptions only, use HttpException.

3fill in blank

hard

Fix the error in the catch method to correctly get the request object.

NestJS

catch(exception: HttpException, host: ArgumentsHost) {
  const ctx = host.switchToHttp();
  const response = ctx.getResponse();
  const request = ctx.[1]();
  const status = exception.getStatus();
  response.status(status).json({
    statusCode: status,
    timestamp: new Date().toISOString(),
    path: request.url,
  });
}

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AgetReq

Brequest

CgetRequestObject

DgetRequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using getReq which is not a method on ArgumentsHost.

Using getRequestObject which does not exist.

Using request which is a property, not a method.

The ArgumentsHost method to get the request object is getRequest().

4fill in blank

hard

Fill both blanks to create a filter that catches multiple exception types.

NestJS

import { ExceptionFilter, Catch, ArgumentsHost, HttpException, BadRequestException } from '@nestjs/common';

@Catch([1], [2])
export class MultiExceptionFilter implements ExceptionFilter {
  catch(exception: any, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const status = exception instanceof HttpException ? exception.getStatus() : 500;
    response.status(status).json({
      statusCode: status,
      message: exception.message || 'Unknown error',
    });
  }
}

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AHttpException

BExceptionFilter

CBadRequestException

DError

Attempts:

3 left

💡 Hint

Common Mistakes

Using ExceptionFilter which is an interface, not an exception class.

Using Error which is too general.

Using the same exception class twice.

The @Catch() decorator can take multiple exception classes to catch. Here, it catches HttpException and BadRequestException.

5fill in blank

hard

Fill all three blanks to create a custom exception filter that logs the error and sends a JSON response.

NestJS

import { ExceptionFilter, Catch, ArgumentsHost, HttpException, Logger } from '@nestjs/common';

@Catch([1])
export class LoggingExceptionFilter implements ExceptionFilter {
  private readonly logger = new [2](LoggingExceptionFilter.name);

  catch(exception: HttpException, host: ArgumentsHost) {
    this.logger.[3](exception.message);
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const status = exception.getStatus();
    response.status(status).json({
      statusCode: status,
      message: exception.message,
    });
  }
}

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AHttpException

BLogger

Cerror

DExceptionFilter

Attempts:

3 left

💡 Hint

Common Mistakes

Using ExceptionFilter instead of HttpException in the decorator.

Using a wrong logger method like 'log' instead of 'error'.

Not creating a Logger instance properly.

The filter catches HttpException, uses the Logger class to create a logger instance, and calls the error method to log the exception message.