service worker

app/views/home/sw.js.erb

@@ -1,10 +1,15 @@
 
+<%
+  pack_assets = [asset_pack_path("application.js"), asset_pack_path("application.css")].select { |a| a.present? }
+%>
+
 var cacheName = "parsley-cache-<%= File.mtime(Webpacker::manifest.config.public_manifest_path).to_i %>";
 
 var staticAssets = [
-  "/",
-  "<%= asset_pack_path("application.js") %>",
-  "<%= asset_pack_path("application.css") %>"
+  "/"
+  <% pack_assets.each do |a| %>
+    ,"<%= a %>"
+  <% end %>
 ];
 
 self.addEventListener('install', function(event) {
@@ -30,11 +35,33 @@ self.addEventListener('activate', function(event) {
 });
 
 self.addEventListener('fetch', function(event) {
-  event.respondWith(
-    caches.match(event.request).then(function (response) {
-      return response || fetch(event.request);
-    })
-  );
+  var reqUrl = new URL(event.request.url);
+  var x, asset;
+
+  for (x = 0; x < staticAssets.length; x++) {
+    asset = staticAssets[x];
+    if (asset === reqUrl.pathname) {
+      event.respondWith(
+        caches.match(event.request).then(function (response) {
+          return response || fetch(event.request);
+        })
+      );
+      return;
+    }
+  }
+
+
+  event.respondWith(caches.open(cacheName).then(function(cache) {
+    return fetch(event.request)
+      .then(function(response) {
+        cache.put(event.request, response.clone());
+        return response;
+      })
+      .catch(function() {
+        return caches.match(event.request);
+      });
+  }));
+
 });
 
 self.addEventListener('message', function (event) {