Add a simple service worker for offline shell

cgen-1bb0676720c6412bade128fbb38b3686

website/public/sw.js

@@ -0,0 +1,26 @@
+const CACHE = 'switch-cache-v1';
+const ASSETS = [
+  '/',
+  '/index.html',
+  '/playground.html',
+  '/monarch.html',
+  '/switch.html'
+];
+self.addEventListener('install', (e) => {
+  e.waitUntil(caches.open(CACHE).then(c=>c.addAll(ASSETS)).then(()=>self.skipWaiting()));
+});
+self.addEventListener('activate', (e) => {
+  e.waitUntil(caches.keys().then(keys=>Promise.all(keys.filter(k=>k!==CACHE).map(k=>caches.delete(k)))).then(()=>self.clients.claim()));
+});
+self.addEventListener('fetch', (e) => {
+  const url = new URL(e.request.url);
+  if (url.origin === location.origin) {
+    e.respondWith(caches.match(e.request).then(r=> r || fetch(e.request).then(resp=>{
+      if (e.request.method==='GET' && resp.ok && resp.type==='basic') {
+        const clone = resp.clone();
+        caches.open(CACHE).then(c=>c.put(e.request, clone));
+      }
+      return resp;
+    }).catch(()=>caches.match('/index.html'))));
+  }
+});