Creating a Simple Web Server

🎯 Goal of This Note

Learn how to create a basic web server using Node.js that can accept requests from a browser and send back responses.

📦 Step 1: Import the `http` Module in `index.js` File

const http = require('http');

The http module is another built-in Node.js module (just like fs).
It gives Node networking capabilities — specifically, the ability to build a web server.

Tip: It's helpful to comment out any earlier file-reading/writing code at this point, and organize your file with comments like // FILES and // SERVER to separate sections clearly.

🛠️ Step 2: Building a Server — Two Main Steps

To create a working server in Node.js, you need to:

Create the server.
Start (listen on) the server so it can accept incoming requests.

🌐 Creating the Server

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

👷‍♂️ Building the Server

http.createServer() creates a new server.
It accepts a callback function that runs every time a new request hits the server.
This callback receives two important objects:
1. req (request) — contains information about the incoming request (e.g., the URL requested, headers, etc.)
2. res (response) — provides tools for sending a response back to the client (browser)

🚀 Sending a Response

res.end('Hello from the server!');

res.end() is the simplest way to send a plain text response back to whoever made the request.
(The reason it's called .end will make more sense later — for now, just know it sends and finishes the response.)

Note: Deeper concepts like "requests," "responses," and the client-server model will be explained in a dedicated upcoming lecture on how the web works. For now, the focus is on getting things working practically first, theory later.

🚀 Step 3: Starting the Server (Listening for Requests)

server.listen(8000, '127.0.0.1', () => {
  console.log('Listening to requests on port 8000');
});

This method is called on the server variable (the result of createServer) and takes:

🚪 Port number — e.g., 8000
- A port is like a sub-address on a specific host/computer.
- Common port numbers used in Node development: 8000, 3000, 80, etc.
🌐 Host (optional)
- '127.0.0.1' is the standard IP address for localhost (meaning "this current computer").
- If not specified, it defaults to localhost automatically.
📢 Callback function (optional)
- Runs once the server successfully starts listening.
- Commonly used to log a confirmation message like:
```
Listening to requests on port 8000
```

▶️ Step 4: Running the Server

In the terminal:

node index.js

You'll see the log message: Listening to requests on port 8000
Unlike previous scripts, this program does NOT exit automatically — it keeps running.
- This is because the server must stay active to keep listening for new requests.
- This behavior relates to something called the event loop, which will be explained in more detail later in the course.

🌐 Step 5: Testing the Server in a Browser

Open a browser.
Go to: (host, followed by a colon :, followed by the port number)
```
localhost:8000 OR 127.0.0.1:8000
```
You should see the message: Hello from the server!

🎉 Congratulations — you now have a real, working web server running on your computer using Node.js!

🛑 Step 6: How to Stop the Server

Unlike the REPL (Ctrl + D), a running Node script is stopped with:

Ctrl + C

(Even on Mac — use Control, not Command.)

This is the standard way to stop any Node script from here on out.

🔍 Step 7: Exploring the Request Object

You can inspect the req (request) object to see what data it contains:

const server = http.createServer((req, res) => {
  console.log(req);
  res.end('Hello from the server!');
});

After making changes to code, remember to:
1. Stop the server (Ctrl + C)
2. Restart it (node index.js)
3. Refresh the browser page to trigger a new request
The req object contains a large amount of data, including:
- HTTP headers (like host)
- Many other properties (too much to display fully in the console)

HTTP headers will be explained in more detail in an upcoming topic.

const fs = require('fs');
const http = require('http');

////////////////////////////
//FILES

//Blocking, Synchronous way
//const textIn = fs.readFileSync('./txt/input.txt', 'utf-8');
//console.log(textIn);

//const textOut = `This is what we know about the avocado: ${textIn}.\nCreated on ${Date.now()}`;
//fs.writeFileSync('./txt/output.txt', textOut);

//console.log('File written!');

//Non-blocking, Asynchronous way
// fs.readFile('./txt/start.txt', 'utf8', (err, data1) => {
//   fs.readFile(`./txt/${data1}.txt`, 'utf8', (err, data2) => {
//     console.log(data2);

//     fs.readFile('./txt/append.txt', 'utf8', (err, data3) => {
//       console.log(data2, data3);

//       fs.writeFile('./txt/final.txt', `${data2}\n${data3}`, 'utf8', (err) => {
//         console.log('Your file has been written 🎉');
//       });
//     });
//   });
// });
/////////////////////////////
//SERVER
const server = http.createServer((req, res) => {
	console.log(req);
  res.end('Hello from the server!');
});

server.listen(8000, '127.0.0.1', () => {
  console.log('Listening to requests on port 8000');
});

🔄 Recap: What Just Happened

🏗️ We created a server using http.createServer(), passing in a callback that runs on every incoming request.
🚀 We started the server using server.listen(), specifying the port and host (localhost).
🌐 When we visited localhost:8000 in the browser, it triggered a request.
⚡ Internally, Node fired an event, which triggered our callback function.
📤 The callback sent back the response: "Hello from the server!"