Custom error classes in Express - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom error class in Express?

A custom error class is a user-defined class that extends the built-in Error class to create specific error types with custom properties or messages, helping to handle errors more clearly in Express apps.

beginner

How do you create a basic custom error class in Express?

You create a class that extends Error, call super(message) in the constructor, and optionally add properties like statusCode to represent HTTP error codes.

intermediate

Why add a statusCode property to a custom error class in Express?

Adding statusCode helps middleware know which HTTP status to send in the response, making error responses clear and consistent.

intermediate

What is the benefit of using custom error classes over plain Error objects in Express?

Custom error classes let you distinguish error types easily, add extra info, and handle different errors in specific ways in middleware.

beginner

Show a simple example of a custom NotFoundError class in Express.

class NotFoundError extends Error {
  constructor(message = 'Not Found') {
    super(message);
    this.name = 'NotFoundError';
    this.statusCode = 404;
  }
}

What must a custom error class extend in Express?

A Error

B Object

C Response

D Request

Custom error classes extend the built-in Error class to inherit error behavior.

Why include a statusCode property in a custom error?

A To store HTTP status for responses

B To log errors to console

C To change request headers

D To modify URL paths

statusCode helps middleware send the right HTTP status code in the response.

Which method is called inside the constructor of a custom error class?

A new Error()

B this.error()

C extend()

D super(message)

super(message) calls the parent Error constructor with the error message.

What is a key advantage of custom error classes in Express?

A They speed up server response

B They allow specific error handling

C They reduce file size

D They replace middleware

Custom errors let you handle different errors in tailored ways.

Which property usually holds the error message in a custom error?

A name

B statusCode

C message

D stack

The message property contains the error description.

Explain how to create and use a custom error class in Express.

Think about how errors flow from route to middleware.

Describe why custom error classes improve error handling in Express applications.

Consider how different errors need different responses.