initial

service_worker.js

@@ -0,0 +1,30 @@
+/*
+Should prevent navigator.serviceWorker.controller from being null on first load, but doesn't work for some reason.
+TODO: compare with
+https://googlechrome.github.io/samples/service-worker/post-message/
+which seems to work on first load
+
+self.addEventListener('install', function(event) {
+  //event.waitUntil(self.skipWaiting()); // Activate worker immediately
+});
+
+self.addEventListener('activate', function(event) {
+  event.waitUntil(self.clients.claim()); // Become available to all pages
+});
+*/
+
+let data
+
+self.addEventListener('message', async function(e) {
+  const msg = e.data
+  let reply
+  if(msg.type == 'SET') {
+    data = msg.data
+    reply = null
+  } else if(msg.type == 'GET') {
+    reply = data
+  } else {
+    throw new Error('unknown message type: ' + msg.type)
+  }
+  e.ports[0].postMessage(reply)
+})