Centralized error handler in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define an error-handling middleware 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 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 an error handler.

2fill in blank

medium

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

Express

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

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

A400

B404

C200

D500

Attempts:

3 left

💡 Hint

Common Mistakes

Using status 200 which means success.

Using status 404 which means not found.

Status code 400 means a bad request. Here, we send the error message as JSON with status 400.

3fill in blank

hard

Fix the error in the middleware to correctly pass the error to the next handler.

Express

app.use(function(err, req, res, next) {
  if (!err) {
    [1]();
  } else {
    res.status(500).send(err.message);
  }
});

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

Areq

Bres

Cnext

Derr

Attempts:

3 left

💡 Hint

Common Mistakes

Calling res() which is not a function.

Calling err() which is not a function.

Calling next() without arguments passes control to the next middleware. This is needed when there is no error.

4fill in blank

hard

Fill both blanks to create a middleware that logs the error message and then passes the error along.

Express

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

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

Alog

Bnext

Cerror

Dwarn

Attempts:

3 left

💡 Hint

Common Mistakes

Using console.error instead of console.log (both work but only one is correct here).

Calling next() without the error argument.

Use console.log to print the error message. Then call next(err) to pass the error to the next middleware.

5fill in blank

hard

Fill all three blanks to create a centralized error handler that sets status, logs error, and sends JSON response.

Express

app.use(function(err, req, res, next) {
  res.status([1]);
  console.[2](err.stack);
  res.json({ error: [3] });
});

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

A500

Berror

Cerr.message

Dwarn

Attempts:

3 left

💡 Hint

Common Mistakes

Using status 200 instead of 500.

Logging with console.log instead of console.error.

Sending the whole error object instead of just the message.

The status code 500 means server error. Use console.error to log the stack trace. Send the error message in JSON response.