update

html/sw.js

@@ -12,47 +12,38 @@ var urlsToCache = [
     './font-awesome-4.7.0/fonts/fontawesome-webfont.woff2?v=4.7.0'
 ];
 
-self.addEventListener('install', function (event) {
+self.addEventListener('install', event => {
     // Perform install steps
     event.waitUntil(
         caches.open(CACHE_NAME)
-            .then(function (cache) {
+            .then(cache => {
                 console.log('Opened cache');
                 return cache.addAll(urlsToCache);
             })
     );
 });
 
-self.addEventListener('fetch', function (event) {
+self.addEventListener('fetch', event => {
     event.respondWith(
-        caches.match(event.request)
-            .then(function (response) {
-                // Cache hit - return response
-                if (response) {
-                    return response;
-                }
+        fetch(event.request).then(response => {
+            // Throw invalid responses away...
+            if (!response || response.status !== 200 || response.type !== 'basic')
+                return response;
 
-                return fetch(event.request).then(
-                    function (response) {
-                        // Check if we received a valid response
-                        if (!response || response.status !== 200 || response.type !== 'basic') {
-                            return response;
-                        }
+            // Cloning the valid reply
+            var responseToCache = response.clone();
 
-                        // IMPORTANT: Clone the response. A response is a stream
-                        // and because we want the browser to consume the response
-                        // as well as the cache consuming the response, we need
-                        // to clone it so we have two streams.
-                        var responseToCache = response.clone();
+            // Storing the valid reply; an upsert into the cache
+            caches.open(CACHE_NAME).then(cache => {
+                cache.put(event.request, responseToCache);
+            });
 
-                        caches.open(CACHE_NAME)
-                            .then(function (cache) {
-                                cache.put(event.request, responseToCache);
-                            });
-
-                        return response;
-                    }
-                );
-            })
+            // Returning the response
+            return response;
+        }, () => {
+            // Failed. It's cache or nothing.
+            return caches.match(event.request);
+        })
     );
 });
+