Routing and JSON bodies by hand

Before the framework

Frameworks feel like magic until you've done it yourself once. Parse the URL, choose a route by method and path, read a JSON body from the request stream — then Express will make perfect sense.

URL, method and body

import http from "node:http";

const dishes = [{ id: 1, name: "Momo", price: 180 }];

async function readJson(req) {
  let raw = "";
  for await (const chunk of req) raw += chunk;
  return raw ? JSON.parse(raw) : {};
}

function send(res, status, data) {
  res.writeHead(status, { "Content-Type": "application/json" });
  res.end(JSON.stringify(data));
}

http
  .createServer(async (req, res) => {
    const url = new URL(req.url, "http://localhost");
    if (req.method === "GET" && url.pathname === "/dishes") {
      const max = Number(url.searchParams.get("max") ?? Infinity);
      return send(res, 200, dishes.filter((d) => d.price <= max));
    }
    if (req.method === "POST" && url.pathname === "/dishes") {
      const body = await readJson(req);
      const dish = { id: dishes.length + 1, name: body.name, price: body.price };
      dishes.push(dish);
      return send(res, 201, dish);
    }
    send(res, 404, { error: "Not found" });
  })
  .listen(3000);

const created = await fetch("http://localhost:3000/dishes", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ name: "Thukpa", price: 220 }),
});
console.log(created.status, await created.json());
console.log(await (await fetch("http://localhost:3000/dishes?max=200")).json());

This works, but grows messy fast: every route is an if-statement, path parameters need regexes, errors need handling everywhere.
That's exactly what Express (next lesson) cleans up.

Before the framework

URL, method and body

The rest of this lesson