Creating a basic HTTP server in Node.js

Introduction

We create an HTTP server to listen for requests from web browsers or other clients and send back responses like web pages or data.

You want to serve a simple web page from your computer.

You need to test how your website works locally before publishing.

You want to build a small API that other programs can talk to.

You want to learn how web servers work by making one yourself.

Syntax

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  // handle request and response here
});

server.listen(3000, () => {
  console.log(`Server running on port 3000`);
});

The http.createServer function creates a server that listens for requests.

The callback receives req (request) and res (response) objects to handle communication.

Examples

This server sends 'Hello World' to every request on port 3000.

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  res.end('Hello World');
});

server.listen(3000);

This server responds differently based on the URL path requested.

Node.js

import http from 'http';

const server = http.createServer((req, res) => {
  if (req.url === '/') {
    res.end('Home page');
  } else {
    res.statusCode = 404;
    res.end('Not found');
  }
});

server.listen(8080);

Sample Program

This program creates a simple HTTP server on port 4000. It sends a plain text message 'Welcome to my server!' for every request. When the server starts, it logs a message to the console.

Node.js

import http from 'http';

const port = 4000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Welcome to my server!');
});

server.listen(port, () => {
  console.log(`Server running on port ${port}`);
});

Important Notes

Always set the correct Content-Type header so browsers know how to display the response.

Use res.end() to finish the response and send data back to the client.

Remember to choose a port number that is free and allowed by your system.

Summary

Creating an HTTP server lets your computer respond to web requests.

Use http.createServer with a function to handle requests and responses.

Start the server with server.listen(port) and check the console for confirmation.

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