Your first web server

What you'll learn

How a server receives a request and sends back a response, using only Node's built-in http module.

Why it matters

Every website and API is a server answering requests. Seeing the smallest possible one removes the mystery before you meet frameworks like Express.

Explanation

The web works as request and response. A browser sends a request (a URL and a method such as GET). A server sends a response (a status code, headers and a body).

Node's http.createServer takes a function called for every request. That function receives:

• req: information about the request, such as req.url and req.method.
• res: your tool for answering. res.writeHead(200, {...}) sets the status and headers and res.end("text") sends the body.

server.listen(3000) starts waiting for connections on port 3000.

Example

Save as server.mjs:

Step-by-step walkthrough

1. createServer is given a function that runs once per request.
2. For /, we answer status 200 (OK) with plain text.
3. For /api/time, we answer with JSON. JSON.stringify turns an object into a string.
4. Anything else gets 404, meaning "not found".
5. listen(3000, ...) starts the server and prints a line. Open http://localhost:3000 in a browser to try it. Stop it with Ctrl+C.

Try it yourself

Run it on your machine and visit the three URLs. The terminal output when it starts is below.

server.mjsNode.js

Editable codeimport http from "node:http"; const server = http.createServer((req, res) => { if (req.url === "/") { res.writeHead(200, { "Content-Type": "text/plain" }); res.end("Hello from my first server"); } else if (req.url === "/api/time") { res.writeHead(200, { "Content-Type": "application/json" }); res.end(JSON.stringify({ ok: true })); } else { res.writeHead(404, { "Content-Type": "text/plain" }); res.end("Not found"); } }); server.listen(3000, () => { console.log("Listening on http://localhost:3000"); });

Show output ResetCopyCtrl+Enter to run

Common mistakes

• Never calling res.end(), so the browser waits forever.
• Port already in use. Another program is on 3000. Pick another port.
• Forgetting to restart the server after editing the file.
• Sending an object directly. res.end needs a string or Buffer, so stringify first.

Quick quiz

Summary

• A server answers requests with responses: status, headers, body.
• http.createServer + listen is the core of every Node web app.
• Frameworks like Express make routing and parsing easier.

You finished the Node.js beginner section. Next: Express, REST APIs and environment variables.

import http from "node:http";

const server = http.createServer((req, res) => {
  if (req.url === "/") {
    res.writeHead(200, { "Content-Type": "text/plain" });
    res.end("Hello from my first server");
  } else if (req.url === "/api/time") {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(JSON.stringify({ ok: true }));
  } else {
    res.writeHead(404, { "Content-Type": "text/plain" });
    res.end("Not found");
  }
});

server.listen(3000, () => {
  console.log("Listening on http://localhost:3000");
});