Building custom middleware 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'

Anext

Bdone

Ccallback

Dhandle

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong parameter name like 'done' or 'callback' instead of 'next'.

Forgetting to call the next function.

The third parameter in Express middleware is always called next. It is a function that passes control to the next middleware.

2fill in blank

medium

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

Node.js

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

app.use([1]);

app.get('/', (req, res) => res.send('Hello'));

app.listen(3000);

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

Aexpress

Blogger

Capp

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the wrong variable like 'express' or 'app' instead of the middleware function.

Forgetting to pass the middleware function to app.use.

To use a middleware, you pass its function name to app.use(). Here, logger is the middleware function.

3fill in blank

hard

Fix the error in the middleware to correctly handle asynchronous operations.

Node.js

async function auth(req, res, [1]) {
  const user = await getUser(req.headers.token);
  if (!user) {
    return res.status(401).send('Unauthorized');
  }
  next();
}

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

Ahandle

Bdone

Ccallback

Dnext

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong parameter name for the next function.

Not calling next() after async checks.

The middleware must call next to pass control. The parameter must be named next to be called correctly.

4fill in blank

hard

Fill both blanks to create middleware that adds a timestamp to the request and calls next.

Node.js

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

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

Anext

Btimestamp

Ctime

Ddate

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong parameter names for next.

Storing timestamp in a wrong property name.

The third parameter must be next to continue the middleware chain. The timestamp is stored in req.timestamp.

5fill in blank

hard

Fill all three blanks to create middleware that checks if user is admin and calls next or sends 403.

Node.js

function checkAdmin(req, res, [1]) {
  if (req.user && req.user.role === [2]) {
    [3];
  } else {
    res.status(403).send('Forbidden');
  }
}

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

Anext

B'admin'

Cnext()

D'user'

Attempts:

3 left

💡 Hint

Common Mistakes

Not calling next() as a function.

Checking for wrong role string.

Using wrong parameter name for next.

The middleware uses next as the third parameter. It checks if req.user.role equals 'admin'. If yes, it calls next() to continue.