Composable Request Handling with Express Middleware

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

// Simple request logger
app.use((req, res, next) => {
  console.log(`${req.method} ${req.url}`);
  next();
});

// Reusable auth guard
function requireAuth(req, res, next) {
  if (!req.headers.authorization) return res.status(401).json({ error: "No token" });
  next();
}

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

// Centralised error handler (4 args = error middleware)
app.use((err, req, res, next) => {
  console.error(err);
  res.status(500).json({ error: "Server error" });
});

app.listen(3000);