Middleware concept and execution flow in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a middleware function that logs the request method.

Node.js

function logger(req, res, [1]) {
  console.log(req.method);
  next();
}

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

Ahandler

Bcallback

Cnext

Ddone

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect parameter names like 'callback' or 'done' instead of 'next'.

The third parameter in middleware functions is always called next. It is used to pass control to the next middleware.

2fill in blank

medium

Complete the code to use the middleware in an Express app.

Node.js

const express = require('express');
const app = express();

app.use([1]);

app.listen(3000);

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

Alogger

Blogger()

Clogger.call()

Dlogger.apply()

Attempts:

3 left

💡 Hint

Common Mistakes

Calling the middleware function immediately by adding parentheses.

When passing middleware to app.use, you pass the function itself without calling it.

3fill in blank

hard

Fix the error in the middleware to ensure it passes control correctly.

Node.js

function checkAuth(req, res, [1]) {
  if (!req.user) {
    res.status(401).send('Unauthorized');
  } else {
    next();
  }
  // Missing call to continue middleware chain
}

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

Acontinue

Bdone

Ccallback

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Not calling next() causing the request to hang.

The middleware must call next() to continue to the next middleware or route handler.

4fill in blank

hard

Fill both blanks to create middleware that modifies the request and passes control.

Node.js

function addRequestTime(req, res, [1]) {
  req.requestTime = Date.now();
  [2]();
}

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

Anext

Bres.send

Cnext()

Dreq.next

Attempts:

3 left

💡 Hint

Common Mistakes

Calling res.send instead of next().

The middleware function receives next as the third parameter and calls next() to continue.

5fill in blank

hard

Fill all three blanks to create middleware that checks a header and either continues or sends an error.

Node.js

function checkHeader(req, res, [1]) {
  if (req.headers['x-api-key'] === '[2]') {
    [3]();
  } else {
    res.status(403).send('Forbidden');
  }
}

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

Anext

B12345

Cnext()

Dcallback

Attempts:

3 left

💡 Hint

Common Mistakes

Not calling next() or using wrong parameter names.

The middleware uses next as the third parameter and calls next() to continue. It checks if the header matches '12345'.