Modified fetcher

static/service-worker.js

@@ -33,6 +33,13 @@ self.addEventListener('activate', function (event) {
     )
 });
 
+self.addEventListener('fetch', function (event) {
+    event.respondWith(
+        fetch(event.request).catch(function() {
+            return caches.match(event.request);
+        })
+    );
+});
 
 function requestBackend(event){
     var url = event.request.clone();