Custom error classes in Node.js - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom error class in Node.js?

A custom error class is a user-defined class that extends the built-in Error class to create specific error types with custom messages or properties.

beginner

Why should you extend the built-in Error class when creating custom errors?

Extending the built-in Error class ensures your custom error behaves like a standard error, including stack traces and compatibility with error handling mechanisms.

beginner

How do you set a custom error message in a custom error class?

You pass the message to the super() call inside the constructor of your custom error class, which sets the message property on the error instance.

intermediate

What is the purpose of setting the name property in a custom error class?

Setting the name property helps identify the error type when logging or handling errors, making it easier to distinguish between different custom errors.

beginner

Show a simple example of a custom error class in Node.js.

class ValidationError extends Error {
  constructor(message) {
    super(message);
    this.name = 'ValidationError';
  }
}

// Usage:
throw new ValidationError('Invalid input');

What must a custom error class in Node.js extend to behave like a standard error?

A Error

B Object

C Function

D Array

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

Which method is used to pass the error message in a custom error class constructor?

A super(message)

B this.message = message

C Error(message)

D setMessage(message)

The super(message) call passes the message to the base Error class constructor.

Why is setting the 'name' property in a custom error class useful?

A To change the error message

B To improve performance

C To fix syntax errors

D To identify the error type

The 'name' property helps identify the error type when handling or logging errors.

What will happen if you throw a custom error without extending Error?

A It behaves exactly like a standard error

B It won't have a stack trace

C It will crash Node.js immediately

D It will automatically extend Error

Without extending Error, the custom error won't have a proper stack trace or behave like a standard error.

Which of these is a correct way to throw a custom error?

A throw Error('ValidationError')

B throw ValidationError('Invalid input')

C throw new ValidationError('Invalid input')

D throw new Error('ValidationError')

You must create an instance of the custom error class using 'new' before throwing it.

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

Think about inheritance and how errors carry messages and names.

Why is it important to extend the built-in Error class when making custom errors?

Consider what makes errors useful when debugging and handling.