Add service worker and cache assets

public/assets/enhancements.js

@@ -54,6 +54,7 @@
         div.innerHTML = '<svg/>';
         return 'classList' in div.firstChild;
       })(),
+      serviceWorker: 'serviceWorker' in navigator
     }
   };
 
@@ -222,6 +223,11 @@
     }
   };
 
+  // Register service worker
+  if(supports.test(['serviceWorker'])) {
+    navigator.serviceWorker.register('/sw.js');
+  }
+
   // Init favourite nodes
   if(supports.test(['localStorage', 'inlineSVG', 'querySelector', 'classList'])) {
     favouriteNodes.init();

public/sw.js

@@ -0,0 +1,48 @@
+var cacheName = 'top-explorer-cache-v1';
+
+// Install
+self.addEventListener('install', function(event) {
+
+  // Cache assets
+  event.waitUntil(
+    caches.open(cacheName)
+      .then(function(cache) {
+        return cache.addAll([
+          '/assets/style.css',
+          '/assets/enhancements.js',
+          '/assets/iconfont.woff',
+          '/assets/heart.svg'
+        ]);
+      })
+  );
+});
+
+// Fetch
+self.addEventListener('fetch', function(event) {
+  var requestUrl = new URL(event.request.url);
+
+  // Only do stuff with our own urls
+  if(requestUrl.origin !== location.origin) {
+    return;
+  }
+
+  // Always check cache for assets
+  if(requestUrl.pathname.startsWith('/assets/')) {
+    checkCacheFirst(event);
+    return;
+  }
+});
+
+// Try cache first, if we don't have it make the request
+function checkCacheFirst(event) {
+  return event.respondWith(
+    caches.match(event.request)
+      .then(function(response) {
+        if (response) {
+          return response;
+        }
+        return fetch(event.request);
+      }
+    )
+  );
+}