ServiceWorkerContainer.controller

当状态为activated 时， ServiceWorkerContainer 接口的只读属性 controller 返回一个 ServiceWorker 对象（与 ServiceWorkerRegistration.active 返回的对象是同一个）。当页面强制刷新 (Shift + refresh) 或不存在active worder时，该属性返回 null 。

var myController = navigator.serviceWorker.controller;

一个ServiceWorker对象.

if ('serviceWorker' in navigator) {
  // Do a one-off check to see if a service worker's in control.
  if (navigator.serviceWorker.controller) {
    console.log('This page is currently controlled by:',
      navigator.serviceWorker.controller);
  } else {
    console.log('This page is not currently controlled ' +
      'by a service worker.');
  }
} else {
  console.log('Service workers are not supported.');
}