Add a simple service worker to make an installable app

modules/restserver/src/main/templates/index.html

@@ -46,6 +46,13 @@
          };
         </script>
         <script type="application/javascript" src="{{appExtraJs}}"></script>
+        <script>
+         if('serviceWorker' in navigator) {
+             navigator.serviceWorker
+                 .register('/sw.js')
+                 .then(function() { console.log("Service Worker Registered"); });
+         }
+        </script>
     </body>
 
 </html>

modules/restserver/src/main/templates/sw.js

@@ -0,0 +1,37 @@
+// use a cacheName for cache versioning
+var cacheName = 'v1:static';
+
+// during the install phase you usually want to cache static assets
+self.addEventListener('install', function(e) {
+    // once the SW is installed, go ahead and fetch the resources to make this work offline
+    e.waitUntil(
+        caches.open(cacheName).then(function(cache) {
+            return cache.addAll([
+                {{# cssUrls }}
+                '{{.}}',
+                {{/ cssUrls }}
+                {{# jsUrls }}
+                '{{.}}',
+                {{/ jsUrls}}
+                '{{appExtraJs}}'
+            ]).then(function() {
+                self.skipWaiting();
+            });
+        })
+    );
+});
+
+// when the browser fetches a url
+self.addEventListener('fetch', function(event) {
+    // either respond with the cached object or go ahead and fetch the actual url
+    event.respondWith(
+        caches.match(event.request).then(function(response) {
+            if (response) {
+                // retrieve from cache
+                return response;
+            }
+            // fetch as normal
+            return fetch(event.request);
+        })
+    );
+});