Building an HTTP Server

Node.js includes a built-in http module that lets you create web servers without installing any external packages. Understanding it is the foundation for frameworks like Express.

Creating a Basic Server

const http = require("http");

const server = http.createServer(function (req, res) {
  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("Hello, World!");
});

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

http.createServer() accepts a callback called a request listener. Node.js calls it every time a client sends an HTTP request. The callback receives two objects:

• req — an IncomingMessage object containing the request URL, method, headers, and body
• res — a ServerResponse object you use to send back status codes, headers, and body content

The Request Object

const server = http.createServer(function (req, res) {
  console.log(req.method);  // 'GET', 'POST', etc.
  console.log(req.url);     // '/about', '/api/users', etc.
  console.log(req.headers); // object of request headers

  res.writeHead(200, { "Content-Type": "text/plain" });
  res.end("OK");
});

Routing by URL

const http = require("http");

const server = http.createServer(function (req, res) {
  if (req.url === "/" && req.method === "GET") {
    res.writeHead(200, { "Content-Type": "text/html" });
    res.end("<h1>Home Page</h1>");
  } else if (req.url === "/about" && req.method === "GET") {
    res.writeHead(200, { "Content-Type": "text/html" });
    res.end("<h1>About Page</h1>");
  } else {
    res.writeHead(404, { "Content-Type": "text/plain" });
    res.end("404 Not Found");
  }
});

server.listen(3000);

Serving JSON

const http = require("http");

const server = http.createServer(function (req, res) {
  if (req.url === "/api/status") {
    const payload = JSON.stringify({ status: "ok", uptime: process.uptime() });
    res.writeHead(200, { "Content-Type": "application/json" });
    res.end(payload);
  } else {
    res.writeHead(404);
    res.end();
  }
});

server.listen(3000);

Reading a Request Body

HTTP POST or PUT requests carry a body. Because bodies arrive in chunks (streams), you must collect them:

const server = http.createServer(function (req, res) {
  if (req.method === "POST" && req.url === "/echo") {
    let body = "";
    req.on("data", function (chunk) {
      body += chunk.toString();
    });
    req.on("end", function () {
      res.writeHead(200, { "Content-Type": "application/json" });
      res.end(body);
    });
  }
});

Why Use a Framework?

Writing routing logic, body parsing, and error handling manually gets tedious fast. That is exactly why frameworks like Express exist — they wrap the http module with a clean, ergonomic API. But knowing how the raw module works makes debugging and understanding frameworks far easier.