feature: directed cache sw

src/scripts/register-sw.js

@@ -1,5 +1,11 @@
-document.addEventListener("DOMContentLoaded", function () {
-  if('serviceWorker' in navigator) {
-    navigator.serviceWorker.register('/sw.js');
-  }
-});
+if('serviceWorker' in navigator) {
+  var refreshing;
+  navigator.serviceWorker.addEventListener('controllerchange', () => {
+      if (refreshing) {
+          return;
+      }
+      refreshing = true;
+      window.location.reload();
+  });
+  navigator.serviceWorker.register('/sw.js');
+}