Custom exception classes in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom exception class in NestJS?

A custom exception class in NestJS is a user-defined class that extends the built-in HttpException class to create specific error types with custom messages and HTTP status codes.

beginner

How do you create a custom exception class in NestJS?

You create a custom exception class by extending the HttpException class and calling its constructor with a message and an HTTP status code.

intermediate

Why use custom exception classes instead of throwing generic errors?

Custom exception classes provide clear, consistent error responses with specific HTTP status codes and messages, making error handling and debugging easier and improving API clarity.

beginner

Example: What does this custom exception class do?
class ForbiddenException extends HttpException {
  constructor() {
    super('Access denied', HttpStatus.FORBIDDEN);
  }
}

This class creates a custom exception named ForbiddenException that returns a 403 Forbidden HTTP status with the message 'Access denied' when thrown.

intermediate

How does NestJS handle custom exceptions when thrown in a controller?

NestJS catches custom exceptions thrown in controllers and automatically sends an HTTP response with the status code and message defined in the exception class.

Which class should you extend to create a custom exception in NestJS?

A Error

B HttpException

C ExceptionFilter

D Controller

Custom exceptions in NestJS extend the HttpException class to leverage built-in HTTP error handling.

What parameters does the HttpException constructor expect?

A Only an HTTP status code

B Only a message

C A message and an HTTP status code

D A request and response object

HttpException constructor requires a message and an HTTP status code to define the error response.

What HTTP status code does HttpStatus.FORBIDDEN represent?

A 401

B 500

C 404

D 403

HttpStatus.FORBIDDEN corresponds to the 403 status code, meaning access is denied.

Why is it better to use custom exceptions instead of generic errors in NestJS?

A They provide specific HTTP status codes and messages

B They run faster

C They require less code

D They automatically fix bugs

Custom exceptions improve clarity by sending specific HTTP status codes and messages.

What happens when a custom exception is thrown inside a NestJS controller?

A NestJS sends an HTTP response with the exception's status and message

B The server crashes

C Nothing happens

D The exception is ignored

NestJS catches the exception and sends an HTTP response with the defined status and message.

Explain how to create and use a custom exception class in NestJS.

Think about extending the built-in error class and how NestJS handles thrown exceptions.

Why are custom exception classes useful in building APIs with NestJS?

Consider how clients and developers benefit from clear and consistent error responses.