Simplify the refresh banner example.

Use a prolyfill of `navigator.serviceWorker.waiting` and `ServiceWorker.skipWaiting()` to simply implementation.

Fixes google#5504

src/content/en/tools/workbox/guides/advanced-recipes.md

@@ -15,11 +15,34 @@ description: Advanced recipes to use with Workbox.
 A common UX pattern for progressive web apps is to show a banner when a service
 worker has updated and waiting to install.
 
-To do this you'll need to add some code to your page and to your service worker.
+To do this you'll need to add some polyfill code to your page and to your service worker.
 
 **Add to your page**
 
 ```javascript
+// polyfill navigator.serviceWorker.waiting
+if (!('waiting' in navigator.serviceWorker)) {
+  navigator.serviceWorker.waiting = new Promise(function(resolve) {
+    navigator.serviceWorker.ready.then(function(reg) {
+      function awaitStateChange() {
+        reg.installing.addEventListener('statechange', function() {
+          if (this.state === 'installed') resolve(reg);
+        });
+      }
+      if (reg.waiting) resolve(reg);
+      if (reg.installing) awaitStateChange();
+      reg.addEventListener('updatefound', awaitStateChange);
+    })
+  });
+}
+
+// polyfill ServiceWorker.skipWaiting()
+if (!('skipWaiting' in ServiceWorker.prototype)) {
+  ServiceWorker.prototype.skipWaiting = function() {
+    this.postMessage('skipWaiting');
+  }
+}
+
 function showRefreshUI(registration) {
   // TODO: Display a toast or refresh UI.
 
@@ -40,79 +63,27 @@ function showRefreshUI(registration) {
 
     button.disabled = true;
 
-    registration.waiting.postMessage('force-activate');
+    registration.waiting.skipWaiting();
   });
 
   document.body.appendChild(button);
 };
 
-function onNewServiceWorker(registration, callback) {
-  if (registration.waiting) {
-    // SW is waiting to activate. Can occur if multiple clients open and
-    // one of the clients is refreshed.
-    return callback();
-  }
-
-  function listenInstalledStateChange() {
-    registration.installing.addEventListener('statechange', function() {
-      if (event.target.state === 'installed') {
-        // A new service worker is available, inform the user
-        callback();
-      }
-    });
-  };
-
-  if (registration.installing) {
-    return listenInstalledStateChange();
-  }
-
-  // We are currently controlled so a new SW may be found...
-  // Add a listener in case a new SW is found,
-  registration.addEventListener('updatefound', listenInstalledStateChange);
-}
-
-window.addEventListener('load', function() {
-  // When the user asks to refresh the UI, we'll need to reload the window
-  navigator.serviceWorker.addEventListener('message', function(event) {
-    if (!event.data) {
-      return;
-    }
-
-    switch (event.data) {
-      case 'reload-window':
-        window.location.reload();
-        break;
-      default:
-        // NOOP
-        break;
-    }
-  });
-
-  navigator.serviceWorker.register('/sw.js')
-  .then(function (registration) {
-      // Track updates to the Service Worker.
-    if (!navigator.serviceWorker.controller) {
-      // The window client isn't currently controlled so it's a new service
-      // worker that will activate immediately
-      return;
-    }
-
-    onNewServiceWorker(registration, function() {
-      showRefreshUI(registration);
-    });
-  });
+navigator.serviceWorker.addEventListener('controllerchange', function() {
+  window.location.reload();
 });
+
+navigator.serviceWorker.waiting.then(showRefreshUI);
 ```
 
-This code handles the verious possible lifecycles of the service worker
+The polyfill handles the verious possible lifecycles of the service worker
 and detects when a new service worker has become installed and is waiting to
 activate.
 
-When a waiting service worker is found we set up a message listener on
-`navigator.serviceWorker` so we know when to reload the window. When the
-user clicks on the UI to refresh the page, we post a message to the new
-service worker telling it to force an activation. After this a message is
-posted to all windows telling them to reload.
+When a waiting service worker is found we we tell the service worker to skip
+waiting (posting a message if necessary). After this, the `controllerchange`
+event will fire. The page should reload when the controller changes to
+ensure that all tabs are running the same version of the code.
 
 Note: This is one possible approach to refreshing the page on a new service
 worker. For a more thorough answer as well as an explanation of alternative
@@ -122,19 +93,18 @@ discuess a range of options.
 
 **Add to your service worker**
 
+This code supports the polyfill while we wait for `ServiceWorker.skipWaiting`
+to be available in all browsers.
+
 ```javascript
 self.addEventListener('message', (event) => {
   if (!event.data){
     return;
   }
 
   switch (event.data) {
-    case 'force-activate':
+    case 'skipWaiting':
       self.skipWaiting();
-      self.clients.claim();
-      self.clients.matchAll().then((clients) => {
-        clients.forEach((client) => client.postMessage('reload-window'));
-      });
       break;
     default:
       // NOOP
@@ -143,10 +113,7 @@ self.addEventListener('message', (event) => {
 });
 ```
 
-This will receive a the 'force-activate' message and call `skipWaiting()` and
-`clients.claim()` so that the service worker activates immediately and controls
-all of the currently open windows. We then message each window with a
-'reload-window' message so each tab is refreshed with the latest content.
+This will receive a 'skipWaiting' message and call `skipWaiting()`.
 
 ## "Warm" the runtime cache