Node.js and Express

const express = require("express");
const app = express();

app.use(express.json());              // parse JSON bodies

app.get("/health", (req, res) => {
  res.json({ status: "ok" });
});

const port = process.env.PORT || 3000;
app.listen(port, () => console.log(`Listening on ${port}`));

const notes = [];

app.get("/notes", (req, res) => res.json(notes));

app.post("/notes", (req, res) => {
  const { text } = req.body;
  if (!text) return res.status(400).json({ error: "text is required" });
  const note = { id: notes.length + 1, text };
  notes.push(note);
  res.status(201).json(note);
});

app.get("/notes/:id", (req, res) => {
  const note = notes.find((n) => n.id === Number(req.params.id));
  if (!note) return res.status(404).json({ error: "not found" });
  res.json(note);
});

function logger(req, res, next) {
  console.log(`${req.method} ${req.url}`);
  next();
}

function requireAuth(req, res, next) {
  if (!req.headers.authorization) return res.status(401).end();
  next();
}

app.use(logger);
app.get("/private", requireAuth, (req, res) => res.json({ ok: true }));

// must have 4 parameters
app.use((err, req, res, next) => {
  console.error(err);
  res.status(500).json({ error: "internal server error" });
});