什么时候会获取更新的预缓存内容，以便可以向用户显示通知？

Question

每当使用Notification API更新预缓存的内容时，我都试图向用户显示通知。在config.onUpdate(registration)中，我通过了registration。每当注册新服务工作者时，都会调用registration.onupdatefound，其中使用navigator.serviceWorker.controller检查serviceWorker是否已“激活” 如果它被激活，那么我正在显示通知。

function registerValidSW(swUrl: string, config?: Config) {
  navigator.serviceWorker
    .register(swUrl)
    .then(registration => {
      Notification.requestPermission();
      registration.onupdatefound = () => {
        const installingWorker = registration.installing;
        if (installingWorker == null) {
          return;
        }
        installingWorker.onstatechange = () => {
          if (installingWorker.state === "installed") {
            if (navigator.serviceWorker.controller) {
              // At this point, the updated precached content has been fetched,
              // but the previous service worker will still serve the older
              // content until all client tabs are closed.
              console.log(
                "New content is available and will be used when all " +
                  "tabs for this page are closed.PWA."
              );
              // Execute callback
              if (config && config.onUpdate) {
                config.onUpdate(registration);
              }
            } else {
              // At this point, everything has been precached.
              // It's the perfect time to display a
              // "Content is cached for offline use." message.
              console.log("Content is cached for offline use.");

              // Execute callback
              if (config && config.onSuccess) {
                config.onSuccess(registration);
              }
            }
          }
        };
      };
    })
    .catch(error => {
      console.error("Error during service worker registration:", error);
    });
}

let config ={
    onUpdate:(registration: ServiceWorkerRegistration)=>{
        if (Notification.permission == 'granted') {
            registration.showNotification('New content is available; please refresh.');
          }
    }
};

预期输出：-只要有更新的预缓存内容就应调用config.onUpdate()。

实际输出：-刷新页面时，我会收到通知。