PushManager.getSubscription()

PushManager 接口的方法PushManager.getSubscription() 尝试获取已有的推送订阅。

它返回一个 Promise 用来resolve出一个包含现有订阅的详细信息的PushSubscription 对象。如果不存在已有的推送订阅，返回null。

​PushManager.getSubscription().then(function(pushSubscription) { ... } );

无。

A Promise that resolves to a PushSubscription object or null.

这个代码片段来自 push messaging and notification sample. (没有能直接运行的例子.)

// We need the service worker registration to check for a subscription
  navigator.serviceWorker.ready.then(function(serviceWorkerRegistration) {
    // Do we already have a push message subscription?
    serviceWorkerRegistration.pushManager.getSubscription()
      .then(function(subscription) {
        // Enable any UI which subscribes / unsubscribes from
        // push messages.
        var pushButton = document.querySelector('.js-push-button');
        pushButton.disabled = false;

        if (!subscription) {
          // We aren’t subscribed to push, so set UI
          // to allow the user to enable push
          return;
        }

        // Keep your server in sync with the latest subscriptionId
        sendSubscriptionToServer(subscription);

        showCurlCommand(subscription);

        // Set your UI to show they have subscribed for
        // push messages
        pushButton.textContent = 'Disable Push Messages';
        isPushEnabled = true;
      })
      .catch(function(err) {
        window.Demo.debug.log('Error during getSubscription()', err);
      });
  });