Add support for postMessage

frontend/src/routes/+layout.svelte

@@ -25,7 +25,7 @@
 			}
 
 			navigator.serviceWorker.ready.then((registration) => {
-				registration.active?.postMessage('Save client');
+				registration.active.postMessage('Save client');
 			});
 		}
 	});

frontend/src/sw.ts

@@ -14,6 +14,12 @@ const ASSETS = [
     ...prerendered // dynamic routes
 ];
 
+let client;
+
+addEventListener('message', event => {
+   client = event.source;
+});
+
 self.addEventListener('install', (event) => {
     // Create a new cache and add all files to it
     async function addFilesToCache() {
@@ -24,7 +30,7 @@ self.addEventListener('install', (event) => {
     event.waitUntil(addFilesToCache());
 });
 
-const channel = new BroadcastChannel('sw-messages');
+
 
 
 self.addEventListener('activate', (event) => {
@@ -36,7 +42,13 @@ self.addEventListener('activate', (event) => {
     }
 
     event.waitUntil(deleteOldCaches());
-    channel.postMessage({title: 'Cache downloaded!'});
+    let channel;
+    if(BroadcastChannel) {
+        channel = new BroadcastChannel('sw-messages');
+        channel.postMessage({title: 'Cache Downloaded'});
+    } else {
+        client.postMessage("Cache Downloaded")
+    }
 });
 
 self.addEventListener('fetch', (event) => {