Why Express for Node.js web servers - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a basic Express server that listens on port 3000.

Express

const express = require('express');
const app = express();
app.get('/', (req, res) => {
  res.send('Hello World!');
});
app.listen([1], () => {
  console.log('Server is running');
});

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

A8080

B5000

C3000

D80

Attempts:

3 left

💡 Hint

Common Mistakes

Using port 80 which requires admin rights

Using a string instead of a number

The number 3000 is the common default port for Express servers in development.

2fill in blank

medium

Complete the code to add middleware that parses JSON bodies in Express.

Express

const express = require('express');
const app = express();
app.use([1]);
app.post('/data', (req, res) => {
  res.json(req.body);
});

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

Aexpress.json()

Bexpress.urlencoded({ extended: true })

Cexpress.static('public')

Dexpress.raw()

Attempts:

3 left

💡 Hint

Common Mistakes

Using urlencoded middleware for JSON

Using static middleware which serves files

express.json() middleware parses incoming JSON requests and puts the parsed data in req.body.

3fill in blank

hard

Fix the error in the route handler to send a JSON response with a message.

Express

app.get('/hello', (req, res) => {
  res.[1]({ message: 'Hi there!' });
});

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

AsendFile

Bjson

Crender

Dredirect

Attempts:

3 left

💡 Hint

Common Mistakes

Using sendFile which expects a file path

Using render without a view engine

res.json() sends a JSON response. Other methods serve files, render views, or redirect.

4fill in blank

hard

Fill both blanks to create a route that responds to PUT requests at '/update'.

Express

app.[1]('/update', (req, res) => {
  res.status([2]).send('Update received');
});

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

Aput

Bpost

Cget

D200

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET or POST instead of PUT

Using status codes like 404 or 500

PUT is the HTTP method for update actions. Status 200 means success.

5fill in blank

hard

Fill all three blanks to create a middleware that logs the request method and URL, then calls next().

Express

app.use((req, res, [1]) => {
  console.log(req.[2] + ' ' + req.[3]);
  next();
});

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

Anext

Bmethod

Curl

Dsend

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting to call next()

Using res.send instead of next

Logging wrong properties

Middleware functions receive next to pass control. req.method and req.url give request info.

Practice

1. Why do many developers choose Express when building web servers with Node.js?

easy

A. Because Express simplifies routing and common web tasks

B. Because Express replaces Node.js entirely

C. Because Express is a database management system

D. Because Express only works with frontend code

Solution

1. Step 1: Understand Express role

   Express is a framework that helps manage routing and web server tasks in Node.js.

2. Step 2: Compare options

   Options A, C, and D describe incorrect roles; Express does not replace Node.js, is not a database, and is backend-focused.

3. Final Answer:

   Because Express simplifies routing and common web tasks -> Option A

4. Quick Check:

   Express simplifies Node.js web servers = B [OK]

Hint: Express helps with routing and web tasks in Node.js [OK]

Common Mistakes:

• Thinking Express replaces Node.js
• Confusing Express with a database
• Assuming Express is only for frontend

2. Which of the following is the correct way to create an Express app in Node.js?

easy

A. const app = new express();

B. const app = express.createApp();

C. const app = express();

D. const app = express.new();

Solution

1. Step 1: Recall Express app creation syntax

   The standard way is calling express() as a function to create the app.

2. Step 2: Check each option

   const app = express(); uses express() correctly; others use invalid or non-existent methods.

3. Final Answer:

   const app = express(); -> Option C

4. Quick Check:

   Express app created by express() = A [OK]

Hint: Use express() function to create app instance [OK]

Common Mistakes:

• Using new keyword with express
• Calling non-existent methods like createApp or new
• Confusing syntax with other frameworks

3. What will the following Express code output when a user visits /hello?

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

medium

A. Server error because of missing response

B. The server crashes due to syntax error

C. Nothing happens because no route is defined

D. The text 'Hello World!' is sent to the browser

Solution

1. Step 1: Analyze route definition

   The code defines a GET route at '/hello' that sends 'Hello World!' as response.

2. Step 2: Understand server behavior

   When visiting '/hello', the server responds with the text 'Hello World!'. No errors or crashes occur.

3. Final Answer:

   The text 'Hello World!' is sent to the browser -> Option D

4. Quick Check:

   GET /hello sends 'Hello World!' = D [OK]

Hint: GET route with res.send sends text to browser [OK]

Common Mistakes:

• Assuming missing response causes error
• Thinking route is undefined
• Confusing syntax errors with correct code

4. Identify the error in this Express server code:

const express = require('express');
const app = express();
app.get('/test', (req, res) => {
  res.send('Test route');
});
app.listen(3000)
console.log('Server running on port 3000');

medium

A. No error; code runs correctly

B. app.listen should have a callback function

C. Missing semicolon after app.listen(3000)

D. res.send is used incorrectly

Solution

1. Step 1: Check syntax and usage

   Semicolons are optional in JavaScript; app.listen without callback is valid.

2. Step 2: Confirm route and response

   Route '/test' correctly sends response; no misuse of res.send.

3. Final Answer:

   No error; code runs correctly -> Option A

4. Quick Check:

   Code syntax and logic are correct = C [OK]

Hint: Semicolons optional; listen callback not required [OK]

Common Mistakes:

• Thinking semicolons are mandatory
• Expecting listen callback always needed
• Misunderstanding res.send usage

5. You want to create an Express server that responds with JSON data at /data and logs each request method and URL. Which code snippet correctly achieves this?

hard

A. const express = require('express');
const app = express();
app.get('/data', (req, res) => {
console.log(req.method, req.url);
res.send('{ message: Hello JSON }');
});
app.listen(3000);

B. const express = require('express');
const app = express();
app.use((req, res, next) => {
console.log(req.method, req.url);
next();
});
app.get('/data', (req, res) => {
res.json({ message: 'Hello JSON' });
});
app.listen(3000);

C. const express = require('express');
const app = express();
app.use((req, res) => {
console.log(req.method, req.url);
});
app.get('/data', (req, res) => {
res.json({ message: 'Hello JSON' });
});
app.listen(3000);

D. const express = require('express');
const app = express();
app.get('/data', (req, res) => {
res.json({ message: 'Hello JSON' });
});
app.listen(3000, () => console.log(req.method, req.url));

Solution

1. Step 1: Understand logging middleware

   const express = require('express'); const app = express(); app.use((req, res, next) => { console.log(req.method, req.url); next(); }); app.get('/data', (req, res) => { res.json({ message: 'Hello JSON' }); }); app.listen(3000); uses app.use with next() to log every request method and URL before passing control.

2. Step 2: Check JSON response correctness

   const express = require('express'); const app = express(); app.use((req, res, next) => { console.log(req.method, req.url); next(); }); app.get('/data', (req, res) => { res.json({ message: 'Hello JSON' }); }); app.listen(3000); uses res.json to send JSON properly at '/data'. Other options either log incorrectly or send string instead of JSON.

3. Final Answer:

   const express = require('express'); const app = express(); app.use((req, res, next) => { console.log(req.method, req.url); next(); }); app.get('/data', (req, res) => { res.json({ message: 'Hello JSON' }); }); app.listen(3000); -> Option B

4. Quick Check:

   Middleware logs + res.json for JSON = A [OK]

Hint: Use middleware with next() to log requests before response [OK]

Common Mistakes:

• Logging inside route only logs that route
• Sending JSON as string instead of using res.json
• Missing next() in middleware causing hang