Recipe: a bounded cache and a local rate limit

const cache = new Map();
export function remember(key, value, ttlMs, now = Date.now()) {
  if (!Number.isFinite(ttlMs) || ttlMs <= 0) throw new RangeError('ttlMs');
  if (cache.size >= 100 && !cache.has(key)) {
    cache.delete(cache.keys().next().value);
  }
  cache.set(key, { value, expires: now + ttlMs });
}
export function readCached(key, now = Date.now()) {
  const entry = cache.get(key);
  if (!entry || entry.expires <= now) {
    cache.delete(key);
    return { hit: false };
  }
  return { hit: true, value: entry.value };
}