Error-handling middleware in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an error-handling middleware function in Express.

Node.js

app.use(function(err, req, res, [1]) {
  res.status(500).send('Something broke!');
});

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

Anext

Berror

Cresponse

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using only three parameters instead of four.

Naming the fourth parameter incorrectly.

The error-handling middleware in Express must have four parameters: err, req, res, and next. The next parameter is required to identify it as error-handling middleware.

2fill in blank

medium

Complete the code to send a JSON error response with status 400.

Node.js

app.use(function(err, req, res, next) {
  res.status([1]).json({ error: err.message });
});

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

A404

B200

C400

D500

Attempts:

3 left

💡 Hint

Common Mistakes

Using 200 which means success.

Using 500 which means server error instead of client error.

Status code 400 means a bad request error. Here, we want to send that status code when an error occurs.

3fill in blank

hard

Fix the error in the middleware signature to correctly handle errors.

Node.js

app.use(function([1], req, res, next) {
  res.status(500).send('Error occurred');
});

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

Aerror

Berr

Cnext

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Placing the error parameter last instead of first.

Using wrong parameter names.

The error-handling middleware must have the error parameter as the first argument. The correct order is err, req, res, next. Here, the error parameter is misplaced and must be fixed.

4fill in blank

hard

Fill both blanks to correctly pass the error to the next middleware.

Node.js

app.use(function(err, req, res, [1]) {
  if (err) {
    [2](err);
  } else {
    next();
  }
});

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

Anext

Bres

Csend

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Calling res or send instead of next.

Using wrong parameter names.

The fourth parameter is next, which is a function to pass control to the next middleware. To forward the error, we call next(err).

5fill in blank

hard

Fill all three blanks to create a middleware that logs the error and sends a 500 response.

Node.js

app.use(function([1], [2], [3], next) {
  console.error([1].message);
  res.status(500).send('Internal Server Error');
});

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

Aerr

Breq

Cres

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of parameters.

Forgetting to log the error message.

The error-handling middleware parameters are err, req, res, and next. We log the error message from err and send a 500 response using res.