Express In-Memory Rate Limiter

const store = new Map();
module.exports = (limit = 100, windowMs = 60000) => (req, res, next) => {
  const key  = req.ip;
  const now  = Date.now();
  const data = store.get(key) || { count: 0, start: now };
  if (now - data.start > windowMs) { data.count = 0; data.start = now; }
  data.count++;
  store.set(key, data);
  if (data.count > limit) return res.status(429).json({ error: 'Too many requests' });
  next();
};