sw.js

//This is the "Offline page" service worker

//Install stage sets up the offline page in the cache and opens a new cache
self.addEventListener('install', function(event) {
	te("pwa", "install", "installed");
	var offlinePage = new Request('offline.htm');
	event.waitUntil(
		fetch(offlinePage).then(function(response) {
			return caches.open('pwabuilder-offline').then(function(cache) {
				console.log('[PWA Builder] Cached offline page during Install ' + response.url);
				return cache.put(offlinePage, response);
			});
		})
	);
});

//If any fetch fails, it will show the offline page.
//Maybe this should be limited to HTML documents?
self.addEventListener('fetch', function(event) {
  event.respondWith(
    fetch(event.request).catch(function(error) {
      console.error( '[PWA Builder] Network request Failed. Serving offline page ' + error );
      return caches.open('pwabuilder-offline').then(function(cache) {
        return cache.match('offline.htm');
      });
    }
  ));
});

//This is a event that can be fired from your page to tell the SW to update the offline page
self.addEventListener('refreshOffline', function(response) {
  return caches.open('pwabuilder-offline').then(function(cache) {
    console.log('[PWA Builder] Offline page updated from refreshOffline event: '+ response.url);
    return cache.put(offlinePage, response);
  });
});