Your First Node.js Server

A web server is a program that waits for requests and sends back responses. When you type an address into a browser, the browser sends a request to a server somewhere on the internet. The server answers with HTML, images, or data. With Node.js you can build that server using the built-in http module, with no installs needed.

Your first server is about ten lines long. It answers every request with a short message. The goal is to see the whole loop: start the server, open a browser, get a response. That loop is the heart of every web application you will ever build, from a blog to an online store. Everything you learn later just adds detail around this same pattern.

Ports deserve a quick word. A port is a numbered door on your computer that a program listens on. Port 3000 is a common choice for development. When you visit http://localhost:3000, localhost means your own machine, and 3000 is the door. If the port is busy, you get an error like EADDRINUSE, meaning another program took the door first. Pick a different port and try again.

To run the server, save the code as app.js, then run node app.js in the terminal. The terminal prints a message and then sits quietly. That quiet is a good sign: the server is running and waiting for visitors. Open http://localhost:3000 in your browser to see the reply. To stop the server, press Ctrl+C in the terminal.

How the code works

Every node js server example follows the same shape: create a server, listen on a port, send a response. The http module provides createServer, which takes a callback that runs on every single request. That callback receives a request object, req, and a response object, res. writeHead sets the status code and content type, end sends the body, and listen starts accepting connections on a port.

const http = require("http");

const server = http.createServer((req, res) => {
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("Hello from Node.js");
});

server.listen(3000, () => {
  console.log("Server running at http://localhost:3000");
});

Run it

Create a folder for this project. Inside it, create a file named app.js and paste the server code. Then open a terminal in that folder and run node app.js. The terminal prints the start message and then stays quiet, which means the server is waiting. Visit http://localhost:3000 and you should see your message. To stop the server, press Ctrl+C.

node app.js

Common mistakes

Two classic beginner errors: forgetting to restart after an edit, and hitting a port conflict. Node.js does not watch your files. Change the code, stop the server with Ctrl+C, and run node app.js again. If the terminal prints EADDRINUSE, another program already owns port 3000. Change the port to 3001, update the address in your browser, and try again.

// Still serving old code? You edited the file but did not restart.
// Stop it with Ctrl+C and run node app.js again.

Syntax

const http = require("http"); // built-in module, no install needed

const server = http.createServer((req, res) => {
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("Hello from Node.js"); // send the reply
});

server.listen(3000, () => {
  console.log("Server running at http://localhost:3000");
});

server.listen(3000).on("error", e=>console.error(e))