Add caching service worker

TODO: Add a build step that automatically caches all posts as well
Signed-off-by: Harsh Shandilya <msfjarvis@gmail.com>

static/service-worker.js

@@ -0,0 +1,38 @@
+const cacheName = 'cache-v1';
+const precacheResources = [
+  '/',
+  '/posts/',
+  'index.html',
+  '/bundle.min.js',
+  '/main.min.css',
+  '/fonts/Inter-UI-Regular.woff2',
+  '/fonts/Inter-UI-Bold.woff2',
+  '/fonts/Inter-UI-Regular.woff',
+  '/fonts/Inter-UI-Bold.woff',
+];
+
+self.addEventListener('install', event => {
+  console.log('Service worker install event!');
+  event.waitUntil(
+    caches.open(cacheName)
+      .then(cache => {
+        return cache.addAll(precacheResources);
+      })
+  );
+});
+
+self.addEventListener('activate', event => {
+  console.log('Service worker activate event!');
+});
+
+self.addEventListener('fetch', event => {
+  console.log('Fetch intercepted for:', event.request.url);
+  event.respondWith(caches.match(event.request)
+    .then(cachedResponse => {
+      if (cachedResponse) {
+        return cachedResponse;
+      }
+      return fetch(event.request);
+    })
+  );
+});

themes/hello-friend-ng/layouts/partials/head.html

@@ -6,6 +6,19 @@
 <meta name="keywords" content="{{ .Site.Params.keywords }}" />
 <meta name="robots" content="noodp" />
 <link rel="canonical" href="{{ .Permalink }}" />
+<script>
+    if ('serviceWorker' in navigator) {
+        window.addEventListener('load', function () {
+            navigator.serviceWorker.register('service-worker.js')
+                .then(reg => {
+                    console.log('Service worker registered!', reg);
+                })
+                .catch(err => {
+                    console.log('Service worker registration failed: ', err);
+                });
+        });
+    }
+</script>
 
 {{ block "title" . }}
 <title>