refactor: wait for save

app/net/client/local.js

@@ -9,6 +9,7 @@ export default class LocalClient extends Client {
     this.worker.addEventListener('message', (event) => {
       if (0 === event.data) {
         this.worker.terminate();
+        this.worker = undefined;
         return;
       }
       this.accept(event.data);

app/routes/_main-menu.play.$.$/route.jsx

@@ -36,9 +36,12 @@ export default function PlaySpecific() {
     if ('local' !== type) {
       return;
     }
-    function onBeforeUnload(event) {
+    async function onBeforeUnload(event) {
       client.disconnect();
-      event.preventDefault();
+      function waitForSave() {
+        return new Promise((resolve) => setTimeout(resolve, 0));
+      }
+      while (client.worker) { await waitForSave(); }
     }
     addEventListener('beforeunload', onBeforeUnload);
     return () => {