How do you create a basic HTTP server in Node.js without Express?

Express is a helpful layer on top of Node's own http module. Underneath, a server is just a function that runs for every incoming request. It receives a req object (what the client sent) and a res object (what you send back), like a shopkeeper who gets an order slip and hands back a parcel.

const http = require("http");

const server = http.createServer((req, res) => {
  if (req.method === "GET" && req.url === "/health") {
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(JSON.stringify({ status: "ok" }));
    return;
  }

  res.writeHead(404, { "Content-Type": "text/plain" });
  res.end("Not found");
});

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

What Express adds on top, and plain http does not give you:

• Routing by path and method with parameters like /users/:id.
• Body parsing; with plain http you read req as a stream and join chunks yourself.
• Middleware chains and handy helpers like res.json() and res.status().

Knowing the raw layer helps in interviews, since Express, Fastify and others are all built on it.

• Forgetting res.end(), so the request hangs.
• Sending a body without a Content-Type header.