Creating a basic HTTP server in Node.js - Practice Exercises

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this basic HTTP server response?

Consider this Node.js HTTP server code. What will the server send back to the client when accessed?

Node.js

import http from 'http';
const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello, world!');
});
server.listen(3000);

A The server responds with JSON: { message: 'Hello, world!' }

B The server responds with plain text: 'Hello, world!'

C The server responds with HTML content containing 'Hello, world!'

D The server throws an error because of missing response end

💡 Hint

Look at the content type and the string passed to res.end.

The server sets the content type to 'text/plain' and sends the string 'Hello, world!' as the response body.

📝 Syntax

intermediate

Which option contains a syntax error in creating an HTTP server?

Identify the option that will cause a syntax error when creating a basic HTTP server in Node.js.

A ;)0003(netsil.revres ;)} ;)'iH'(dne.ser { >= )ser ,qer((revreSetaerc.ptth = revres tsnoc ;'ptth' morf ptth tropmi

B const http = require('http'); const server = http.createServer((req, res) => { res.end('Hi'); }); server.listen(3000);

C import http from 'http'; const server = http.createServer((req, res) => { res.end('Hi'); }); server.listen(3000);

D mport http from 'http'; const server = http.createServer((req, res) => { res.end('Hi'); }); server.listen(3000);

💡 Hint

Look for missing punctuation or misplaced code inside the callback.

Option C is missing a semicolon or closing brace before calling server.listen, causing a syntax error.

❓ state_output

advanced

What is the value of 'count' after 3 client requests?

This server counts how many requests it has handled. What is the value of 'count' after 3 requests?

Node.js

import http from 'http';
let count = 0;
const server = http.createServer((req, res) => {
  count++;
  res.end(`Request number: ${count}`);
});
server.listen(3000);

A 3

B 1

C 0

D Undefined

💡 Hint

The count variable increases each time the server handles a request.

Each request increments count by 1, so after 3 requests, count is 3.

🔧 Debug

advanced

Which option causes the server to crash on request?

One of these server codes will crash when a client makes a request. Identify which one.

A import http from 'http'; const server = http.createServer((req, res) => { res.end('OK'); res.end('Again'); }); server.listen(3000);

B import http from 'http'; const server = http.createServer((req, res) => { res.end('OK'); }); server.listen(3000);

C import http from 'http'; const server = http.createServer((req, res) => { res.write('OK'); }); server.listen(3000);

D import http from 'http'; const server = http.createServer((req, res) => { res.statusCode = 200; res.end('OK'); }); server.listen(3000);

💡 Hint

Check if the response is properly ended.

Option A calls res.end twice, causing a 'write after end' error that crashes the server.

🧠 Conceptual

expert

What happens if server.listen is called twice on the same port?

Consider calling server.listen(3000) twice on the same HTTP server instance. What will happen?

A The server listens twice on port 3000 without error.

B The server restarts and resets all state.

C The server silently ignores the second listen call.

D The second call throws an error because the port is already in use.

💡 Hint

Ports can only be bound once per server instance.

Calling listen twice on the same port causes an error because the port is already bound.

Practice

1. What does the http.createServer() function do in Node.js?

easy

A. It compiles JavaScript code into machine code.

B. It creates a database connection for storing data.

C. It creates a server that listens for HTTP requests and sends responses.

D. It formats JSON data for sending over the network.

Solution

1. Step 1: Understand the purpose of http.createServer()

   This function sets up a server that waits for HTTP requests from clients like browsers.

2. Step 2: Identify what the server does

   The server uses a function to handle incoming requests and send back responses, enabling communication over the web.

3. Final Answer:

   It creates a server that listens for HTTP requests and sends responses. -> Option C

4. Quick Check:

   HTTP server creation = It creates a server that listens for HTTP requests and sends responses. [OK]

Hint: Remember: createServer sets up the web server [OK]

Common Mistakes:

• Confusing server creation with database connection
• Thinking it compiles code
• Mixing up data formatting with server setup

2. Which of the following is the correct way to start a Node.js HTTP server on port 3000?

easy

A. http.listen(3000);

B. server.listen(3000);

C. server.start(3000);

D. server.run(3000);

Solution

1. Step 1: Identify the method to start the server

   The correct method to make the server listen on a port is listen().

2. Step 2: Match the method with the server object

   Calling server.listen(3000); starts the server on port 3000.

3. Final Answer:

   server.listen(3000); -> Option B

4. Quick Check:

   Start server with listen() = server.listen(3000); [OK]

Hint: Use listen() to start the server on a port [OK]

Common Mistakes:

• Using non-existent methods like start() or run()
• Calling listen() on http instead of server
• Confusing server methods with other modules

3. What will the following Node.js code output when accessed via a browser?

const http = require('http');
const server = http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/plain'});
  res.end('Hello World');
});
server.listen(4000);

medium

A. Hello World

B. Error: server.listen is not a function

C. 404 Not Found

D. Hello

Solution

1. Step 1: Analyze the server response setup

   The server sets the HTTP status to 200 (OK) and content type to plain text, then sends 'Hello World' as the response body.

2. Step 2: Understand what the browser receives

   When accessed, the browser will display the exact string 'Hello World' from the server response.

3. Final Answer:

   Hello World -> Option A

4. Quick Check:

   Response text = Hello World [OK]

Hint: Check res.end() content for output text [OK]

Common Mistakes:

• Expecting an error due to incorrect method
• Confusing status codes with output text
• Assuming partial output without reading res.end()

4. Identify the error in this Node.js HTTP server code:

const http = require('http');
const server = http.createServer((req, res) => {
  res.writeHead(200, {'Content-Type': 'text/html'});
  res.write('Welcome');
  res.end();
});
server.listen(8080)
console.log('Server running on port 8080');

medium

A. Incorrect Content-Type header value

B. Using res.write() without res.end() causes error

C. Missing semicolon after server.listen(8080)

D. No error; code runs correctly and serves 'Welcome'

Solution

1. Step 1: Check syntax and method usage

   The code correctly calls res.write() followed by res.end(), which is valid to send response data.

2. Step 2: Verify headers and server start

   The Content-Type is valid as 'text/html', and server.listen(8080) starts the server properly. Missing semicolons are optional in JavaScript.

3. Final Answer:

   No error; code runs correctly and serves 'Welcome' -> Option D

4. Quick Check:

   Valid server code = No error; code runs correctly and serves 'Welcome' [OK]

Hint: res.write() + res.end() is valid to send response [OK]

Common Mistakes:

• Thinking missing semicolons cause errors
• Believing res.write() must be avoided
• Assuming wrong Content-Type causes failure

5. You want to create a Node.js HTTP server that responds with JSON data {"status":"ok"} and sets the correct header. Which code snippet correctly does this?

hard

A. const server = http.createServer((req, res) => {
res.writeHead(200, {'Content-Type': 'application/json'});
res.end(JSON.stringify({status: 'ok'}));
});

B. const server = http.createServer((req, res) => {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('{"status":"ok"}');
});

C. const server = http.createServer((req, res) => {
res.writeHead(404, {'Content-Type': 'application/json'});
res.end(JSON.stringify({status: 'ok'}));
});

D. const server = http.createServer((req, res) => {
res.writeHead(200);
res.end({status: 'ok'});
});

Solution

1. Step 1: Set correct Content-Type header for JSON

   The header must be 'application/json' to tell the client the response is JSON data.

2. Step 2: Send JSON string as response body

   Use JSON.stringify() to convert the object to a JSON string before sending with res.end().

3. Final Answer:

   Code snippet with application/json header and JSON.stringify() -> Option A

4. Quick Check:

   JSON header + stringified data = const server = http.createServer((req, res) => { res.writeHead(200, {'Content-Type': 'application/json'}); res.end(JSON.stringify({status: 'ok'})); }); [OK]

Hint: Use application/json header and JSON.stringify() [OK]

Common Mistakes:

• Sending object directly without stringifying
• Using wrong Content-Type header
• Sending JSON string with text/plain header
• Using 404 status instead of 200