Built-in HTTP exceptions in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to throw a 404 Not Found exception in a NestJS controller.

NestJS

throw new [1]();

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

ANotFoundException

BBadRequestException

CUnauthorizedException

DForbiddenException

Attempts:

3 left

💡 Hint

Common Mistakes

Using BadRequestException instead of NotFoundException.

Confusing UnauthorizedException with NotFoundException.

The NotFoundException is used to throw a 404 error in NestJS.

2fill in blank

medium

Complete the code to import the built-in HTTP exceptions from NestJS.

NestJS

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

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

AInjectable

BController

CModule

DHttpException

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Controller or Module instead of HttpException.

Forgetting to import from '@nestjs/common'.

The HttpException class is the base for all built-in HTTP exceptions in NestJS.

3fill in blank

hard

Fix the error in throwing a 400 Bad Request exception with a custom message.

NestJS

throw new [1]('Invalid input');

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

ANotFoundException

BBadRequestException

CUnauthorizedException

DForbiddenException

Attempts:

3 left

💡 Hint

Common Mistakes

Using NotFoundException for bad input errors.

Using UnauthorizedException for validation errors.

The BadRequestException is used to indicate a 400 error with a custom message.

4fill in blank

hard

Fill both blanks to throw a 403 Forbidden exception with a custom message.

NestJS

throw new [1]('[2]');

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

AForbiddenException

BUnauthorized

CBadRequestException

DNotFoundException

Attempts:

3 left

💡 Hint

Common Mistakes

Using UnauthorizedException instead of ForbiddenException for 403 errors.

Not providing a message string.

The ForbiddenException throws a 403 error. The message can be any string, here we use 'Unauthorized'.

5fill in blank

hard

Fill all three blanks to throw a 401 Unauthorized exception with a custom message and import it correctly.

NestJS

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

throw new [2]('[3]');

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

AUnauthorizedException

BForbiddenException

CBad credentials

DNotFoundException

Attempts:

3 left

💡 Hint

Common Mistakes

Importing the wrong exception class.

Using a message that does not explain the error.

Import and throw UnauthorizedException with a message like 'Bad credentials' to indicate a 401 error.

Practice

1. What is the purpose of using built-in HTTP exceptions like NotFoundException in a NestJS controller?

easy

A. To automatically log all requests to the server

B. To create new API routes dynamically

C. To improve database query performance

D. To send a clear HTTP error response with the correct status code and message

Solution

1. Step 1: Understand the role of HTTP exceptions in NestJS

   Built-in HTTP exceptions are used to send error responses with specific HTTP status codes and messages.

2. Step 2: Identify the purpose of NotFoundException

   This exception sends a 404 status code with a message indicating the resource was not found.

3. Final Answer:

   To send a clear HTTP error response with the correct status code and message -> Option D

4. Quick Check:

   HTTP exceptions = clear error responses [OK]

Hint: Exceptions send proper HTTP status codes and messages [OK]

Common Mistakes:

• Thinking exceptions log requests automatically
• Confusing exceptions with database operations
• Assuming exceptions create routes

2. Which of the following is the correct way to throw a BadRequestException in a NestJS controller method?

easy

A. throw new BadRequestException('Invalid input');

B. return BadRequestException('Invalid input');

C. throw BadRequestException('Invalid input');

D. BadRequestException.throw('Invalid input');

Solution

1. Step 1: Recall the syntax for throwing exceptions in NestJS

   Exceptions are thrown using the JavaScript throw new ExceptionClass() syntax.

2. Step 2: Check the correct usage for BadRequestException

   The correct syntax is throw new BadRequestException('message').

3. Final Answer:

   throw new BadRequestException('Invalid input'); -> Option A

4. Quick Check:

   Throw exceptions with throw new [OK]

Hint: Use 'throw new ExceptionName()' to raise exceptions [OK]

Common Mistakes:

• Omitting 'new' keyword when throwing exceptions
• Using return instead of throw
• Calling exception as a function without 'new'

3. Given this NestJS controller method, what HTTP status code will the client receive?

async getUser(id: string) {
  if (!id) {
    throw new BadRequestException('ID is required');
  }
  const user = await this.userService.findById(id);
  if (!user) {
    throw new NotFoundException('User not found');
  }
  return user;
}

medium

A. 200 if user found, 400 if ID missing, 404 if user not found

B. 200 always

C. 500 if user not found

D. 400 if user not found

Solution

1. Step 1: Analyze the conditions for exceptions

   If id is missing, it throws BadRequestException (HTTP 400). If user is not found, it throws NotFoundException (HTTP 404).

2. Step 2: Understand the normal return

   If no exceptions are thrown, the method returns the user with HTTP 200 status.

3. Final Answer:

   200 if user found, 400 if ID missing, 404 if user not found -> Option A

4. Quick Check:

   Exceptions map to HTTP codes 400 and 404, else 200 [OK]

Hint: Check exception types to know HTTP status codes sent [OK]

Common Mistakes:

• Assuming 500 error instead of 404 for not found
• Ignoring the BadRequestException case
• Thinking exceptions return 200 status

4. Identify the error in this NestJS controller snippet that tries to throw a ForbiddenException:

if (!user.isAdmin) {
  ForbiddenException('Access denied');
}

medium

A. Exception class name is incorrect

B. Missing 'throw' keyword before the exception

C. Exception message should be an object, not a string

D. ForbiddenException cannot be used in controllers

Solution

1. Step 1: Check how exceptions are thrown in NestJS

   Exceptions must be thrown using the throw keyword followed by new ExceptionClass().

2. Step 2: Identify the missing part in the code

   The code calls ForbiddenException('Access denied') without throw and new, so it does nothing.

3. Final Answer:

   Missing 'throw' keyword before the exception -> Option B

4. Quick Check:

   Always use 'throw new Exception()' to raise errors [OK]

Hint: Always use 'throw new' to raise exceptions [OK]

Common Mistakes:

• Calling exception as a function without throw
• Forgetting the 'new' keyword
• Using wrong exception class names

5. You want to create a custom error response with status 403 and a detailed message using NestJS built-in exceptions. Which approach correctly extends ForbiddenException to add a custom error code in the response body?

hard

A. class CustomForbiddenException extends ForbiddenException {
constructor() {
super('Access denied');
this.errorCode = 123;
}
}

B. throw new ForbiddenException('Access denied', 123);

C. class CustomForbiddenException extends ForbiddenException {
constructor() {
super({ message: 'Access denied', errorCode: 123 });
}
}

D. throw new ForbiddenException({ message: 'Access denied' }, 123);

Solution

1. Step 1: Understand how to customize exception response body

   Passing an object to super() in the exception constructor customizes the JSON response.

2. Step 2: Check which option correctly extends ForbiddenException

   class CustomForbiddenException extends ForbiddenException { constructor() { super({ message: 'Access denied', errorCode: 123 }); } } passes an object with message and errorCode to super(), correctly customizing the response.

3. Step 3: Identify why other options are incorrect

   throw new ForbiddenException('Access denied', 123); incorrectly passes a second argument as number; class CustomForbiddenException extends ForbiddenException { constructor() { super('Access denied'); this.errorCode = 123; } } sets a property but does not affect response body; throw new ForbiddenException({ message: 'Access denied' }, 123); passes wrong parameters.

4. Final Answer:

   class CustomForbiddenException extends ForbiddenException { constructor() { super({ message: 'Access denied', errorCode: 123 }); } } -> Option C

5. Quick Check:

   Pass object to super() to customize exception response [OK]

Hint: Pass an object with details to super() in custom exception [OK]

Common Mistakes:

• Passing multiple arguments instead of one object
• Setting properties without calling super() properly
• Misunderstanding how to customize exception response