服务人员-为什么要延长事件的生存期？

Question

in this example

self.addEventListener('notificationclick', function(event) {
console.log('On notification click: ', event.notification.tag);
event.notification.close();

// This looks to see if the current is already open and
// focuses if it is
event.waitUntil(clients.matchAll({
type: "window"
}).then(function(clientList) {
  for (var i = 0; i < clientList.length; i++) {
    var client = clientList[i];
    if (client.url == '/' && 'focus' in client)
    return client.focus();
  }
  if (clients.openWindow)
    return clients.openWindow('/');
}));
});

even.waitUntil() is necessary for the function to properly work because it extends the events' lifetime. But why do you need it? Why can't the promise simply be resolved after event has returned? Thank you!

Answer 1

In this case we need event.waitUntil because client.focus and clients.openWindow are only allowed when called as the result of a notification click event (to protect users from windows opening without their permission). Without event.waitUntil you run the risk of the event returning before clients.openWindow or client.focus is called, in which case the browser will give you this error:

Uncaught (in promise) DOMException: Not allowed to open a window.

See the answer to this post and the openWindow reference on MDN .