FetchEvent

self.addEventListener("fetch", (event) => {
  // GET 
  if (event.request.method !== "GET") return;

  // 
  event.respondWith(
    (async () => {
      // 
      const cache = await caches.open("dynamic-v1");
      const cachedResponse = await cache.match(event.request);

      if (cachedResponse) {
        // 
        // 
        event.waitUntil(cache.add(event.request));
        return cachedResponse;
      }

      // 
      return fetch(event.request);
    })(),
  );
});