获取 PushManager 订阅时出错 - JavaScript

我有以下代码，用于注册服务工作人员并要求用户允许通知。在用户允许推送通知（其中承诺返回）后，我收到错误serviceWorkerRegistration.pushManager.getSubscription() is null。当我关闭浏览器并再次强制调用此函数时，它可以正常工作，不会出现错误。我不明白为什么。这是我的代码：

window.vapidPublicKey = new Uint8Array([4, 45, ...]); 
if (navigator.serviceWorker) {
  navigator.serviceWorker.register('/serviceworker.js')
  .then(function(reg) {
     console.log('Service worker change, registered the service worker');
  });
}
// Otherwise, no push notifications :(
else {
  console.error('Service worker is not supported in this browser');
}

navigator.serviceWorker.ready.then((serviceWorkerRegistration) => {
  console.log("ready");
  serviceWorkerRegistration.pushManager
  .subscribe({
    userVisibleOnly: true,
    applicationServerKey: window.vapidPublicKey
  });
});



// application.js

// Let's check if the browser supports notifications
if (!("Notification" in window)) {
  console.error("This browser does not support notifications.");
}

// Let's check whether notification permissions have already been granted
else if (Notification.permission === "granted") {
  console.log("Permission to receive notifications has been granted");
}

// Otherwise, we need to ask the user for permission
else if (Notification.permission !== 'denied') {
  Notification.requestPermission(function (permission) {
    // If the user accepts, let's create a notification
    if (permission === "granted") {
      console.log("Permission to receive notifications has been granted");
      saveSubscriptionToDatabase();
    }
  });
}

function saveSubscriptionToDatabase(){

      navigator.serviceWorker.ready
      .then((serviceWorkerRegistration) => {
        console.log(serviceWorkerRegistration.pushManager.getSubscription());
        serviceWorkerRegistration.pushManager.getSubscription()
        .then((subscription) => {
          $.post("/users/save_subscription", { subscription: subscription.toJSON() });
        });
      });

}

错误：

Uncaught (in promise) TypeError: Cannot read property 'toJSON' of null
at serviceWorkerRegistration.pushManager.getSubscription.then

UPDATE:

所以我添加了以下按钮：

 <input type="button" onclick="saveSubscriptionToDatabase();" value="test">

只要我从按钮单击调用该函数，所有 JS 和 post 请求都会按预期工作，但是当我从检查权限状态的条件调用它时，它仍然像以前一样失败。

更新2：

我尝试再次编写代码，但从不同的角度。

function registerServiceWorker() {
  return navigator.serviceWorker.register('serviceworker.js')
  .then(function(registration) {
    console.log('Service worker successfully registered.');
    return registration;
  })
  .catch(function(err) {
    console.error('Unable to register service worker.', err);
  });
}


function askPermission() {
  return new Promise(function(resolve, reject) {
    const permissionResult = Notification.requestPermission(function(result) {
      resolve(result);
    });

    if (permissionResult) {
      permissionResult.then(resolve, reject);
    }
  })
  .then(function(permissionResult) {
    if (permissionResult !== 'granted') {
      throw new Error('We weren\'t granted permission.');
    }
  });
}


function subscribeUserToPush() {
  return navigator.serviceWorker.register('serviceworker.js')
  .then(function(registration) {
    const subscribeOptions = {
      userVisibleOnly: true,
      applicationServerKey: new Uint8Array("key goes here")

    };

    return registration.pushManager.subscribe(subscribeOptions);
  })
  .then(function(pushSubscription) {
    console.log("never called");
    console.log('Received PushSubscription: ', JSON.stringify(pushSubscription));
    return pushSubscription;
  });
}

registerServiceWorker();
askPermission();
subscribeUserToPush();

命令链的最后一部分subscribeUserToPush()我在哪里console.log("never called");永远不会执行并且没有错误。我正在 Chrome 67 中对此进行测试。我确信registration.pushManager.subscribe(subscribeOptions);叫做。

因此，经过几个小时的尝试不同的事情后，我终于解决了问题，而且它非常简单。所以每次你打电话navigator.serviceWorker.register('serviceworker.js')你必须放一个/文件名之前。服务人员无需注册即可正常注册/但抢订阅会失败。您在文档中找到的示例不包括/.

所以，代码应该是这样的：

navigator.serviceWorker.register('/serviceworker.js')

田田现在可以了......