diff --git a/js/service-worker.js b/js/service-worker.js
new file mode 100644
index 0000000..f5ed189
--- /dev/null
+++ b/js/service-worker.js
@@ -0,0 +1,102 @@
+/*
+ Copyright 2015 Google Inc. All Rights Reserved.
+ Licensed under the Apache License, Version 2.0 (the "License");
+ you may not use this file except in compliance with the License.
+ You may obtain a copy of the License at
+ http://www.apache.org/licenses/LICENSE-2.0
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+*/
+
+'use strict';
+
+// Incrementing CACHE_VERSION will kick off the install event and force previously cached
+// resources to be cached again.
+const CACHE_VERSION = 1;
+let CURRENT_CACHES = {
+  offline: 'offline-v' + CACHE_VERSION
+};
+const OFFLINE_URL = 'offline.html';
+
+function createCacheBustedRequest(url) {
+  let request = new Request(url, {cache: 'reload'});
+  // See https://fetch.spec.whatwg.org/#concept-request-mode
+  // This is not yet supported in Chrome as of M48, so we need to explicitly check to see
+  // if the cache: 'reload' option had any effect.
+  if ('cache' in request) {
+    return request;
+  }
+
+  // If {cache: 'reload'} didn't have any effect, append a cache-busting URL parameter instead.
+  let bustedUrl = new URL(url, self.location.href);
+  bustedUrl.search += (bustedUrl.search ? '&' : '') + 'cachebust=' + Date.now();
+  return new Request(bustedUrl);
+}
+
+self.addEventListener('install', event => {
+  event.waitUntil(
+    // We can't use cache.add() here, since we want OFFLINE_URL to be the cache key, but
+    // the actual URL we end up requesting might include a cache-busting parameter.
+    fetch(createCacheBustedRequest(OFFLINE_URL)).then(function(response) {
+      return caches.open(CURRENT_CACHES.offline).then(function(cache) {
+        return cache.put(OFFLINE_URL, response);
+      });
+    })
+  );
+});
+
+self.addEventListener('activate', event => {
+  // Delete all caches that aren't named in CURRENT_CACHES.
+  // While there is only one cache in this example, the same logic will handle the case where
+  // there are multiple versioned caches.
+  let expectedCacheNames = Object.keys(CURRENT_CACHES).map(function(key) {
+    return CURRENT_CACHES[key];
+  });
+
+  event.waitUntil(
+    caches.keys().then(cacheNames => {
+      return Promise.all(
+        cacheNames.map(cacheName => {
+          if (expectedCacheNames.indexOf(cacheName) === -1) {
+            // If this cache name isn't present in the array of "expected" cache names,
+            // then delete it.
+            console.log('Deleting out of date cache:', cacheName);
+            return caches.delete(cacheName);
+          }
+        })
+      );
+    })
+  );
+});
+
+self.addEventListener('fetch', event => {
+  // We only want to call event.respondWith() if this is a navigation request
+  // for an HTML page.
+  // request.mode of 'navigate' is unfortunately not supported in Chrome
+  // versions older than 49, so we need to include a less precise fallback,
+  // which checks for a GET request with an Accept: text/html header.
+  if (event.request.mode === 'navigate' ||
+      (event.request.method === 'GET' &&
+       event.request.headers.get('accept').includes('text/html'))) {
+    console.log('Handling fetch event for', event.request.url);
+    event.respondWith(
+      fetch(event.request).catch(error => {
+        // The catch is only triggered if fetch() throws an exception, which will most likely
+        // happen due to the server being unreachable.
+        // If fetch() returns a valid HTTP response with an response code in the 4xx or 5xx
+        // range, the catch() will NOT be called. If you need custom handling for 4xx or 5xx
+        // errors, see https://github.com/GoogleChrome/samples/tree/gh-pages/service-worker/fallback-response
+        console.log('Fetch failed; returning offline page instead.', error);
+        return caches.match(OFFLINE_URL);
+      })
+    );
+  }
+
+  // If our if() condition is false, then this fetch handler won't intercept the request.
+  // If there are any other fetch handlers registered, they will get a chance to call
+  // event.respondWith(). If no fetch handlers call event.respondWith(), the request will be
+  // handled by the browser as if there were no service worker involvement.
+});