Third-party middleware usage in Node.js - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Express middleware package.

Node.js

const express = require('[1]');

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

Ahttp

Bpath

Cfs

Dexpress

Attempts:

3 left

💡 Hint

Common Mistakes

Using core Node.js modules like 'http' instead of 'express'.

Misspelling the package name.

The Express middleware package is imported using require('express').

2fill in blank

medium

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

Node.js

app.[1](middlewareFunction);

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

Aget

Blisten

Cuse

Dpost

Attempts:

3 left

💡 Hint

Common Mistakes

Using route methods like 'get' or 'post' instead of 'use'.

Trying to call 'listen' to add middleware.

Use app.use() to apply middleware functions in Express.

3fill in blank

hard

Fix the error in the middleware function signature.

Node.js

function middleware(req, [1], next) {
  console.log('Middleware running');
  next();
}

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

Aresponse

Bres

Cnext

Drequest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'next' as the second parameter instead of the third.

Using incorrect parameter names.

The middleware function parameters are req, res, and next.

4fill in blank

hard

Fill both blanks to import and use the 'cors' middleware in Express.

Node.js

const [1] = require('cors');
app.[2]([1]());

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

Acors

Blisten

Cuse

Dexpress

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'listen' instead of 'use' to apply middleware.

Importing the wrong package.

Import 'cors' with require('cors') and use it with app.use(cors()).

5fill in blank

hard

Fill all three blanks to import, configure, and use the 'helmet' middleware with options.

Node.js

const [1] = require('helmet');
const helmetOptions = { contentSecurityPolicy: false };
app.[2]([1]([3]));

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

Ahelmet

Buse

ChelmetOptions

Dcors

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing 'cors' with 'helmet'.

Not passing options to the middleware function.

Import 'helmet', then use app.use(helmet(helmetOptions)) to apply it with options.

Practice

1. What is the main purpose of using third-party middleware in a Node.js Express app?

easy

A. To replace the Express framework completely

B. To add extra features without writing them from scratch

C. To write all server code manually

D. To make the app run without Node.js

Solution

1. Step 1: Understand middleware role

   Middleware adds features like logging or parsing to an app without extra coding.

2. Step 2: Compare options

   Only To add extra features without writing them from scratch correctly describes middleware's purpose; others are incorrect or unrelated.

3. Final Answer:

   To add extra features without writing them from scratch -> Option B

4. Quick Check:

   Middleware adds features [OK]

Hint: Middleware adds features without extra coding [OK]

Common Mistakes:

• Thinking middleware replaces Express
• Believing middleware runs without Node.js
• Confusing middleware with full app code

2. Which of the following is the correct way to add a third-party middleware called helmet to an Express app?

easy

A. use.app(helmet);

B. app.helmet();

C. helmet(app);

D. app.use(helmet());

Solution

1. Step 1: Recall Express middleware syntax

   Middleware is added using app.use() with the middleware function called.

2. Step 2: Check options

   Only app.use(helmet()); uses app.use(helmet()); correctly; others have wrong syntax.

3. Final Answer:

   app.use(helmet()); -> Option D

4. Quick Check:

   Middleware added with app.use() [OK]

Hint: Use app.use() with middleware function call [OK]

Common Mistakes:

• Forgetting parentheses after middleware name
• Using incorrect method names like app.helmet()
• Passing middleware without calling it

3. Given this code snippet, what will be the output when a GET request is made to '/'?

const express = require('express');
const morgan = require('morgan');
const app = express();
app.use(morgan('tiny'));
app.get('/', (req, res) => {
  res.send('Hello World');
});
app.listen(3000);

medium

A. Throws an error because morgan is not used correctly

B. Responds with 'Hello World' but no logs appear

C. Logs request details in console and responds with 'Hello World'

D. Server crashes on start

Solution

1. Step 1: Understand morgan middleware

   Morgan logs HTTP request info to the console when used with app.use().

2. Step 2: Analyze code behavior

   GET '/' triggers morgan logging and sends 'Hello World' response.

3. Final Answer:

   Logs request details in console and responds with 'Hello World' -> Option C

4. Quick Check:

   morgan logs + response sent [OK]

Hint: Morgan logs requests when used with app.use() [OK]

Common Mistakes:

• Assuming morgan changes response content
• Thinking morgan causes errors if used like this
• Ignoring middleware effect on logging

4. Identify the error in this code that tries to use the cors middleware:

const express = require('express');
const cors = require('cors');
const app = express();
app.use(cors);
app.get('/', (req, res) => res.send('OK'));
app.listen(3000);

medium

A. Missing parentheses when calling cors middleware

B. cors middleware is not installed

C. app.get() is missing a callback function

D. app.listen() is called without a port

Solution

1. Step 1: Check middleware usage

   Middleware must be called as a function: cors(), not just cors.

2. Step 2: Verify code

   Code uses app.use(cors); missing parentheses, causing error.

3. Final Answer:

   Missing parentheses when calling cors middleware -> Option A

4. Quick Check:

   Middleware must be called with () [OK]

Hint: Always call middleware as a function with () [OK]

Common Mistakes:

• Passing middleware reference without ()
• Assuming app.get() lacks callback
• Forgetting to specify port in listen

5. You want to add both helmet for security and express.json() for parsing JSON bodies in your Express app. Which code correctly adds both middlewares in the right order?

hard

A. app.use(helmet()); app.use(express.json());

B. app.use(express.json); app.use(helmet);

C. app.use(helmet); app.use(express.json);

D. app.use(express.json()); app.use(helmet());

Solution

1. Step 1: Understand middleware order importance

   Security middleware like helmet should run before body parsing for best protection.

2. Step 2: Check middleware calls

   Both must be called as functions with parentheses; options B and C miss these, A has them but wrong order.

3. Step 3: Confirm correct order and syntax

   app.use(helmet()); app.use(express.json()); calls helmet first, then express.json(), both correctly called.

4. Final Answer:

   app.use(helmet()); app.use(express.json()); -> Option A

5. Quick Check:

   Helmet before json, both called [OK]

Hint: Call middleware with () and order security before parsing [OK]

Common Mistakes:

• Not calling middleware as functions
• Placing parsing before security middleware
• Mixing up middleware order