Cleaned up JS scripts and added service worker

static/serviceworker.js

@@ -0,0 +1,91 @@
+let version = 'v1::';
+let cacheName = 'website';
+let offlinePage = '/offline';
+let offlineFundamentals = [offlinePage, '/'];
+let maxItems = 100;
+
+self.addEventListener('install', function (event) {
+	// Cache offline fundamentals
+	event.waitUntil(caches.open(version + cacheName).then(function (cache) {
+        return cache.addAll(offlineFundamentals);
+	}));
+});
+
+function trimCache(name, maxItems) {
+    caches.open(name).then(function(cache) {
+      cache.keys().then(function(keys) {
+        if (keys.length > maxItems) {
+          cache.delete(keys[0]).then(trimCache(name, maxItems));
+        }
+      });
+    });
+}
+
+// Listens for trimCache command which occurs on page load
+self.addEventListener('message', event => {
+    if (event.data.command == 'trimCache') {
+      trimCache(version + cacheName, maxItems);
+    }
+  });
+
+
+// If the version changes, invalidate the cache
+self.addEventListener('activate', function (event) {
+    event.waitUntil(
+        caches.keys()
+            .then(function (keys) {
+                // Remove caches whose name is no longer valid
+                return Promise.all(keys
+                    .filter(function (key) {
+                      return key.indexOf(version) !== 0;
+                    })
+                    .map(function (key) {
+                      return caches.delete(key);
+                    })
+                );
+            })
+    );
+});
+
+// Listen for request events
+self.addEventListener('fetch', function (event) {
+	let request = event.request;
+
+    // Always fetch non-GET requests from the network
+    if (request.method !== 'GET') {
+        event.respondWith(
+            fetch(request)
+                .catch(function () {
+                    return caches.match(offlinePage);
+                })
+        );
+        return;
+    }
+
+    let isRequestType = function(name) { return request.headers.get('Accept').includes(name); }
+
+	// Network-first Approach
+	event.respondWith(
+        // Attepmt to grab the latest copy from the network
+		fetch(request).then(function (response) {
+			// If successful, create a copy of the response
+            // and save it to the cache
+			let cacheCopy = response.clone();
+			event.waitUntil(caches.open(version + cacheName).then(function (cache) {
+				return cache.put(request, cacheCopy);
+			}));
+			return response;
+
+		}).catch(function (error) {
+            // Otherwise, check the cache.
+            return caches.match(request).then(function (response) {
+                // Show offline page if cache misses for HTML pages.
+                if (isRequestType('text/html')) {
+                    return response || caches.match(offlinePage);
+                }
+                return response;
+                
+            });
+		})
+	);
+});