Do not hardcode WebSocket URL

src/app/websocket.service.ts

@@ -31,7 +31,7 @@ export class WebSocketService {
     // observer subscribes. This socket is shared with subsequent observers
     // and closed when the observer count falls to zero.
     this.downlink = jsonWebsocketConnect(
-      'ws://localhost:4242/ws',
+      'ws://' + window.location.host + '/ws',
       this.uplink = new QueueingSubject<object>()
     ).messages.pipe(
         map(message => <WSMessage<undefined>> message),