Why error handling is critical in Express - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a basic error handler middleware in Express.

Express

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

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

Ares

Bresponse

Cerror

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'next' instead of 'res' as the third parameter.

Omitting the error parameter 'err'.

The error handler middleware in Express must have four parameters: err, req, res, and next. Here, res is the response object used to send the error message.

2fill in blank

medium

Complete the code to catch errors in an async route handler using Express.

Express

app.get('/data', async (req, res, [1]) => {
  try {
    const data = await fetchData();
    res.json(data);
  } catch (err) {
    next(err);
  }
});

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

Aresponse

Berror

Cres

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to include 'next' as a parameter.

Trying to handle errors without calling 'next(err)'.

The next function is used to pass errors to Express's error handler. It must be included as the third parameter in the route handler.

3fill in blank

hard

Fix the error in the middleware to properly handle errors in Express.

Express

function errorHandler(err, req, res, [1]) {
  res.status(500).json({ message: err.message });
}

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

Anext

Berror

Cresponse

Dres

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'res' or 'response' instead of 'next' as the fourth parameter.

Omitting the fourth parameter entirely.

The fourth parameter in an Express error handler middleware must be next to properly handle the error flow.

4fill in blank

hard

Fill both blanks to create a middleware that logs errors and passes them on.

Express

function logErrors(err, [1], [2], next) {
  console.error(err.stack);
  next(err);
}

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

Areq

Bres

Crequest

Dresponse

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'request' and 'response' instead of 'req' and 'res'.

Swapping the order of parameters.

The error logging middleware receives err, req, res, and next as parameters. Here, req and res represent the request and response objects.

5fill in blank

hard

Fill all three blanks to create a custom error class and use it in Express.

Express

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

app.use((err, req, res, next) => {
  if (err instanceof [3]) {
    res.status(err.status).send(err.message);
  } else {
    next(err);
  }
});

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

AHttpError

B404

DCustomError

Attempts:

3 left

💡 Hint

Common Mistakes

Using different names for the class and instance check.

Setting status as a string instead of a number.

This code defines a custom error class named CustomError that extends the built-in Error. It sets a status property, here 404. The middleware checks if the error is an instance of CustomError to handle it properly.