Error-handling middleware signature in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Express

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

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

Arequest

Bres

Cerror

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using only three parameters instead of four.

Naming the last parameter incorrectly.

Omitting the next parameter.

The error-handling middleware in Express must have four parameters: err, req, res, and next. The next parameter is required even if unused.

2fill in blank

medium

Complete the code to correctly call the next middleware in an error handler.

Express

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

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

Ares

Bnext

Cerr

Dreq

Attempts:

3 left

💡 Hint

Common Mistakes

Calling res() instead of next().

Forgetting to call next().

Passing the error to next when no error exists.

In Express, calling next() passes control to the next middleware. Here, if there is no error, we call next() to continue.

3fill in blank

hard

Fix the error in the middleware signature to make it a valid error handler.

Express

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

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

Aerr

Brequest

Cnext

Derror

Attempts:

3 left

💡 Hint

Common Mistakes

Placing err last instead of first.

Using only three parameters.

Misnaming parameters.

Error-handling middleware must have four parameters in this order: err, req, res, next. The code had the wrong order and missing err as first parameter.

4fill in blank

hard

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

Express

app.use(function([1], req, res, [2]) {
  console.error([1]);
  [2]([1]);
});

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

Aerr

Bnext

Cres

Dreq

Attempts:

3 left

💡 Hint

Common Mistakes

Using res or req instead of err or next.

Not calling next(err) to pass the error.

The error object is err and the function to pass control is next. The middleware logs the error and calls next(err) to continue error handling.

5fill in blank

hard

Fill all three blanks to send a JSON error response with status 500.

Express

app.use(function([1], req, [2], [3]) {
  [2].status(500).json({ error: [1].message });
});

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

Aerr

Bres

Cnext

Dreq

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up req and res parameters.

Omitting the next parameter.

Not sending a JSON response.

The error object is err, the response object is res, and next is the last parameter. The middleware sends a JSON response with the error message and status 500.