next() function and flow control in Express - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to call the next middleware function in Express.

Express

app.use((req, res, [1]) => {
  console.log('Middleware 1');
  [1]();
});

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

Aend

Bsend

Cnext

Dlisten

Attempts:

3 left

💡 Hint

Common Mistakes

Using res.send() instead of next() to continue middleware.

Forgetting to call next() causing the request to hang.

In Express, the next function is used to pass control to the next middleware.

2fill in blank

medium

Complete the code to skip to the next middleware when a condition is met.

Express

app.use((req, res, next) => {
  if (req.user) {
    [1]();
  } else {
    res.status(401).send('Unauthorized');
  }
});

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

Ares.redirect

Bnext

Cres.end

Dres.send

Attempts:

3 left

💡 Hint

Common Mistakes

Sending a response and then calling next(), which causes errors.

Not calling next() and blocking the request.

Calling next() passes control to the next middleware if the user exists.

3fill in blank

hard

Fix the error in the middleware to properly handle errors and pass them to the error handler.

Express

app.use((req, res, next) => {
  try {
    throw new Error('Something went wrong');
  } catch (err) {
    [1](err);
  }
});

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

Anext

Bconsole.log

Cres.status

Dres.send

Attempts:

3 left

💡 Hint

Common Mistakes

Logging the error but not passing it to next(), so error handlers are not triggered.

Sending a response inside catch and then calling next(), causing headers errors.

Passing the error to next(err) tells Express to skip normal middleware and go to error handlers.

4fill in blank

hard

Fill both blanks to create middleware that logs the request and then passes control to the next middleware.

Express

app.use(([1], [2], next) => {
  console.log(`Request URL: $[1].url`);
  next();
});

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

Areq

Bres

Crequest

Dresponse

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names that don't match Express conventions.

Forgetting to call next() to continue the middleware chain.

The first two parameters are req and res by convention in Express middleware.

5fill in blank

hard

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

Express

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

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

Aerr

Bres

Creq

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the order of parameters in error middleware.

Not sending a response after logging the error.

Error-handling middleware has four parameters: err, req, res, and next. Here, err is used to log the error, res to send the response, and req is the request object.