javascript - 订阅之前，请等待ServiceWorker完成注册

我正在使用ServiceWorker来实现用户通知。当用户首次访问该站点并批准该通知时，ServiceWorker将被注册并订阅:

if ('serviceWorker' in navigator) {
 console.log('Service Worker is supported');
 navigator.serviceWorker.register('/js/sw.js').then(function(reg) {
   if(/chrom(e|ium)/.test(navigator.userAgent.toLowerCase())){
       reg.pushManager.subscribe({
           userVisibleOnly: true
       }).then(function(sub) {
           console.log('endpoint:', sub.endpoint);
           endpoint = sub.endpoint;
           fetch(MY_API+encodeURIComponent(endpoint), {
                    credentials: 'include'
                 })
       });
   }
 }).catch(function(err) {
   console.log(':^(', err);
 });
}

第一次访问时，此操作失败:

Uncaught (in promise) DOMException: Subscription failed - no active Service Worker

从第二次访问开始，一切正常，因为ServiceWorker当时已经处于事件状态。看来这是一个计时问题。在尝试订阅之前，如何确定ServiceWorker已成功注册并处于事件状态？

我尝试使用navigator.serviceWorker.ready，如下所示:

if ('serviceWorker' in navigator) {
 console.log('Service Worker is supported');
 navigator.serviceWorker.register('/js/sw.js').then(function(sreg) {
   console.log(':^)', sreg);
   navigator.serviceWorker.ready.then(function(reg) {
       if(/chrom(e|ium)/.test(navigator.userAgent.toLowerCase())){
           reg.pushManager.subscribe({
               userVisibleOnly: true
           }).then(function(sub) {
               console.log('endpoint:', sub.endpoint);
               endpoint = sub.endpoint;
               fetch("https://www.wettfreun.de/?page=fetch&s=1&endpoint="+encodeURIComponent(endpoint), {credentials: 'include'})
           });
       }
   });
 }).catch(function(err) {
   console.log(':^(', err);
 });
}

现在navigator.serviceWorker.ready.then()内部的部分不再被调用。

最佳答案

您可以使用ServiceWorkerContainer.ready。

来自MDN的示例:

function subscribe() {
  var subscribeButton = document.querySelector('.js-subscribe-button');
  subscribeButton.disabled = false;

  navigator.serviceWorker.ready.then(function(serviceWorkerRegistration) {
    serviceWorkerRegistration.pushManager.subscribe()
      .then(function(subscription) {
        // The subscription was successful
        subscribeButton.disabled = true;
        return sendSubscriptionToServer(subscription);
      })
      .catch(function(error) {
        if (Notification.permission === 'denied') {
          console.log('Permission for Notifications was denied');
          subscribeButton.disabled = true;
        } else {
          console.log('Unable to subscribe to push.', error);
          subscribeButton.disabled = false;
        }
      });
  });
}

关于javascript - 订阅之前，请等待ServiceWorker完成注册，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/35847393/