Began Setup of Service Worker

Add js file for Service Worker to begin process of caching files for offline mode.

index.html

@@ -185,6 +185,20 @@
     		</div>
         </div>
 
+        <!-- Checks is there is a service worker and adds or updates -->
+        <!-- <script>
+            if ('serviceWorker' in navigator) {
+              window.addEventListener('load', () => {
+                navigator.serviceWorker.register('sw.js')
+                .then(swReg => {
+                  console.log('Service Worker is registered', swReg);
+                })
+                .catch(err => {
+                  console.error('Service Worker Error', err);
+                });
+              });
+            }
+        </script> -->
         <!-- <script src="js/vendor/modernizr-3.5.0.min.js"></script> -->
         <script>window.jQuery || document.write('<script src="js/vendor/jquery-3.2.1.min.js"><\/script>')</script>
 

sw.js

@@ -0,0 +1,65 @@
+const filesToCache = [
+  '/',
+  'style/main.css',
+  'images/still_life_medium.jpg',
+  'index.html',
+  'pages/offline.html',
+  'pages/404.html'
+];
+
+const staticCacheName = 'pages-cache-v1';
+
+self.addEventListener('install', event => {
+  console.log('Attempting to install service worker and cache static assets');
+  event.waitUntil(
+    caches.open(staticCacheName)
+    .then(cache => {
+      return cache.addAll(filesToCache);
+    })
+  );
+});
+
+self.addEventListener('fetch', event => {
+  console.log('Fetch event for ', event.request.url);
+  event.respondWith(
+    caches.match(event.request)
+    .then(response => {
+      if (response) {
+        console.log('Found ', event.request.url, ' in cache');
+        return response;
+      }
+      console.log('Network request for ', event.request.url);
+      return fetch(event.request)
+      .then(response => {
+        // TODO 5 - Respond with custom 404 page
+        return caches.open(staticCacheName).then(cache => {
+          cache.put(event.request.url, response.clone());
+          return response;
+      });
+    });
+
+    }).catch(error => {
+
+      // TODO 6 - Respond with custom offline page
+
+    })
+  );
+});
+
+self.addEventListener('activate', event => {
+  console.log('Activating new service worker...');
+
+  const cacheWhitelist = [staticCacheName];
+
+  event.waitUntil(
+    caches.keys().then(cacheNames => {
+      return Promise.all(
+        cacheNames.map(cacheName => {
+          if (cacheWhitelist.indexOf(cacheName) === -1) {
+            return caches.delete(cacheName);
+          }
+        })
+      );
+    })
+  );
+});