16. Creating an HTTP server

Node ships a full HTTP server in `node:http`. A request handler receives `(req, res)`: `req` is a readable stream describing the incoming request, `res` is a writable stream you use to send a response.

js
import { createServer } from "node:http";

const server = createServer((req, res) => {
  if (req.url === "/health") {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(JSON.stringify({ ok: true }));
    return;
  }
  res.writeHead(404);
  res.end("not found");
});

server.listen(3000, () => console.log("listening on :3000"));

Frameworks like Express build convenience on top of this same primitive (routing, middleware, body parsing) — understanding the raw `http` module makes those abstractions much less mysterious.

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