controlled-promise.js

/**
@license
Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
This code may only be used under the BSD style license found at
http://polymer.github.io/LICENSE.txt The complete set of authors may be found at
http://polymer.github.io/AUTHORS.txt The complete set of contributors may be
found at http://polymer.github.io/CONTRIBUTORS.txt Code distributed by Google as
part of the polymer project is also subject to an additional IP rights grant
found at http://polymer.github.io/PATENTS.txt
*/
// Provides an equivalent to navigator.serviceWorker.ready that waits for the
// page to be controlled, as opposed to waiting for the active service worker.
// See https://github.com/slightlyoff/ServiceWorker/issues/799
window._controlledPromise = new Promise(function(resolve) {
  // Resolve with the registration, to match the .ready promise's behavior.
  var resolveWithRegistration = function() {
    navigator.serviceWorker.getRegistration().then(function(registration) {
      resolve(registration);
    });
  };

  if (navigator.serviceWorker.controller) {
    resolveWithRegistration();
  } else {
    navigator.serviceWorker.addEventListener(
        'controllerchange', resolveWithRegistration);
  }
});