Custom error classes in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a custom error class named MyError.

Express

class MyError extends [1] {
  constructor(message) {
    super(message);
    this.name = 'MyError';
  }
}

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

AError

BFunction

CArray

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Extending from Object or Array instead of Error.

Forgetting to call super(message) in the constructor.

The custom error class should extend the built-in Error class to behave like an error.

2fill in blank

medium

Complete the code to throw the custom error with a message.

Express

throw new MyError([1]);

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

Anull

B123

Ctrue

D'Something went wrong'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a number or boolean instead of a string.

Forgetting quotes around the message.

Errors usually carry a descriptive message as a string.

3fill in blank

hard

Fix the error in the custom error class to properly set the prototype chain.

Express

class CustomError extends Error {
  constructor(message) {
    super(message);
    this.name = 'CustomError';
    [1];
  }
}

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

AObject.setPrototypeOf(this, CustomError.prototype)

Bthis.prototype = CustomError

Cthis.__proto__ = Error.prototype

DCustomError.prototype = this

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning prototype incorrectly causing instanceof to fail.

Using deprecated or wrong prototype assignments.

Setting the prototype chain with Object.setPrototypeOf(this, CustomError.prototype) ensures instanceof works correctly.

4fill in blank

hard

Fill both blanks to create a middleware function that catches CustomError and sends a 400 status.

Express

function errorHandler(err, req, res, next) {
  if (err instanceof [1]) {
    res.status([2]).send({ error: err.message });
  } else {
    next(err);
  }
}

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

ACustomError

B400

C500

DError

Attempts:

3 left

💡 Hint

Common Mistakes

Using generic Error instead of CustomError in instanceof.

Sending wrong status code like 500 for client errors.

The middleware checks if the error is a CustomError and sends a 400 Bad Request status.

5fill in blank

hard

Fill all three blanks to define a custom error with a status code property and use it in middleware.

Express

class [1] extends Error {
  constructor(message) {
    super(message);
    this.status = [2];
    this.name = '[3]';
  }
}

function handler(err, req, res, next) {
  res.status(err.status || 500).send({ error: err.message });
}

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

AValidationError

B400

DCustomError

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatch between class name and error name string.

Forgetting to set the status property.

The class is named ValidationError, has a status 400, and sets the name accordingly for clear error handling.