BackgroundFetchUpdateUIEvent

addEventListener("backgroundfetchsuccess", (event) => {
  const bgFetch = event.registration;
  event.waitUntil(
    (async () => {
      // キャッシュを作成
      const cache = await caches.open("downloads");
      // すべての BackgroundFetchRecord オブジェクトを取得
      const records = await bgFetch.matchAll();
      // 各リクエスト/レスポンスの組をコピー
      const promises = records.map(async (record) => {
        const response = await record.responseReady;
        await cache.put(record.request, response);
      });
      // コピーの完了を待つ
      await Promise.all(promises);
      // 進捗表示を更新
      event.updateUI({ title: "Episode 5 ready to listen!" });
    })(),
  );
});