now it is PWA

sw.js

@@ -0,0 +1,35 @@
+const CACHE = 'otaman-v1';
+const URLS = [
+  'index.html',
+  'style.css',
+  'sim.png',
+  'icon-192.png',
+  'icon-512.png',
+  'manifest.json',
+  'des-bundle.js',
+];
+
+self.addEventListener('install', e => {
+  e.waitUntil(
+    caches.open(CACHE).then(c => c.addAll(URLS))
+  );
+  self.skipWaiting();
+});
+
+self.addEventListener('activate', e => {
+  e.waitUntil(
+    caches.keys().then(keys =>
+      Promise.all(keys.filter(k => k !== CACHE).map(k => caches.delete(k)))
+    )
+  );
+});
+
+self.addEventListener('fetch', e => {
+  e.respondWith(
+    caches.match(e.request).then(r => r || fetch(e.request).then(res => {
+      const clone = res.clone();
+      caches.open(CACHE).then(c => c.put(e.request, clone));
+      return res;
+    }))
+  );
+});