frontend/script/service-worker.js.tmpl

self.addEventListener("push", function(event) {
  var data;
  if (event.data) {
    data = event.data.json();
    event.waitUntil(self.registration.showNotification(data.title, data));
  }
});
self.addEventListener('notificationclick', function(event) {
  var url;

  if (!event.notification.data || !event.notification.data.url) {
    return;
  }

  event.notification.close();
  url = event.notification.data.url;

  if (!url) return;

  event.waitUntil(
    clients.matchAll({
      type: 'window',
    })
    .then(function (windowClients) {
      var i;
      var client;
      for (i = 0; i < windowClients.length; i++) {
        client = windowClients[i];
        if (client.url === url && 'focus' in client) {
            return client.focus();
        }
      }
      if (clients.openWindow) {
        return clients.openWindow(url);
      }
      return undefined;
    })
  );
});