Synchronous error handling in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create an Express error handler middleware.

Express

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

Omitting the next parameter causes Express not to recognize the middleware as an error handler.

The error handler middleware in Express must have four parameters: err, req, res, and next. The next parameter is required even if not used.

2fill in blank

medium

Complete the code to throw a synchronous error inside a route handler.

Express

app.get('/', (req, res) => {
  throw new [1]('Oops!');
});

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

AException

BError

CString

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Throwing a string instead of an Error object prevents Express from handling the error properly.

To throw an error in JavaScript, use the Error constructor. This creates a proper error object that Express can catch.

3fill in blank

hard

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

Express

app.use((req, res, next) => {
  const err = new Error('Not found');
  [1](err);
});

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

Anext

Bthrow

Cres.send

Dreturn

Attempts:

3 left

💡 Hint

Common Mistakes

Using throw inside async middleware causes unhandled exceptions.

Calling res.send does not forward the error.

To pass an error to the next middleware in Express, call next(err). Throwing the error or returning it does not work here.

4fill in blank

hard

Fill both blanks to create an error handler that logs the error and sends a 500 status.

Express

app.use(function(err, req, res, [1]) {
  console.[2](err.message);
  res.status(500).send('Server error');
});

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

Anext

Blog

Cerror

Dwarn

Attempts:

3 left

💡 Hint

Common Mistakes

Using console.log instead of console.error for errors.

Omitting the next parameter.

The error handler middleware must have next as the fourth parameter. To log errors, use console.error for clear error messages.

5fill in blank

hard

Fill all three blanks to create a route that catches synchronous errors and passes them to the error handler.

Express

app.get('/data', (req, res, [1]) => {
  try {
    throw new [2]('Failed to load data');
  } catch (err) {
    [3](err);
  }
});

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

Anext

BError

Dres

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to call next(err) inside the catch block.

Using res instead of next to forward errors.

The third parameter in route handlers is next. Use Error to create an error object. Call next(err) inside catch to forward the error.