ServiceWorker.state

【ServiceWorker.state】

ServiceWorker.state

　　The state read-only property of the ServiceWorker interface returns a string representing the current state of the service worker. It can be one of the following values: installing, installed, activating, activated, or redundant.

ServiceWorkerRegistration.installing

　　The installing property of the ServiceWorkerRegistration interface returns a service worker whoseServiceWorker.state is installing. This property is initially set to null.

ServiceWorkerRegistration.waiting

　　The waiting property of the ServiceWorkerRegistration interface returns a service worker whoseServiceWorker.state is installed. This property is initially set to null.

ServiceWorkerRegistration.active

　　The active property of the ServiceWorkerRegistration interface returns a service worker whoseServiceWorker.state is activating or activated. This property is initially set to null.

var serviceWorker;
if (registration.installing) {
  serviceWorker = registration.installing;
  document.querySelector('#kind').textContent = 'installing';
} else if (registration.waiting) {
  serviceWorker = registration.waiting;
  document.querySelector('#kind').textContent = 'waiting';
} else if (registration.active) {
  serviceWorker = registration.active;
  document.querySelector('#kind').textContent = 'active';
}

if (serviceWorker) {
  logState(serviceWorker.state);
  serviceWorker.addEventListener('statechange', function(e) {
  logState(e.target.state);
  });
}

ServiceWorkerContainer.controller

　　The controller read-only property of the ServiceWorkerContainer interface returns a ServiceWorker object if its state is activated (the same object returned by ServiceWorkerRegistration.active). This property returns null if the request is a force refresh (Shift + refresh) or if there is no active worker.

参考：

1、https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorker/state

2、https://developer.mozilla.org/en-US/docs/Web/API/ServiceWorkerRegistration/waiting