Your First App

Relax. We'll talk through this in plain words — no textbook voice.

As your first Node.js app, you'll build a web server that replies with Hello World whenever the browser sends a request. This lesson is where the Node.js backend mindset really begins—a request comes in, and the server sends back a response.

javascript

// File: app.js
const http = require('http');

const hostname = '127.0.0.1';
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain; charset=utf-8');
  res.end('Hello World from Node.js\n');
});

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

require('http') pulls in Node.js's built-in HTTP module. The function inside http.createServer() runs every time a request comes in. res.end() is where the response gets sent back to the browser/client.

You should see

Server running at http://127.0.0.1:3000/ Browser result: Hello World from Node.js

Info

Don't close the terminal while the server is running—closing it will stop the server. After you change the code, stop the server with Ctrl + C and run it again.

Easy traps

If you see "Port 3000 already in use", another app is already using port 3000. Try switching to port 3001 and running it again.

Exercise

This pattern is the foundation of every web server. Once you understand checking a request and sending back a response, you're ready to build APIs, authentication, and dashboard backends.

You'll know it worked when: