Use templates for WSMessage

src/app/test-button/test-button.component.ts

@@ -19,7 +19,7 @@ export class TestButtonComponent implements OnInit {
   }
 
   ngOnInit() {
-    this.webSocketService.observeAnchor(this.anchor_id).subscribe((event) => {
+    this.webSocketService.observeAnchor<string>(this.anchor_id).subscribe((event) => {
       this.text = event.data;
     });
   }

src/app/websocket.service.ts

@@ -16,7 +16,7 @@ function jsonWebsocketConnect(url: string, input: Observable<object>, protocols?
 @Injectable()
 export class WebSocketService {
   private uplink: QueueingSubject<object>;
-  public downlink: Observable<WSMessage>;
+  public downlink: Observable<WSMessage<undefined>>;
 
   constructor() {
 
@@ -40,8 +40,8 @@ export class WebSocketService {
     console.log('ws connected');
   }
 
-  public observeAnchor(anchor: string): Observable<WSMessage> {
-    return this.downlink.filter(message => message.anchor === anchor);
+  public observeAnchor<T>(anchor: string): Observable<WSMessage<T>> {
+    return this.downlink.pipe(filter(message => message.anchor === anchor));
   }
 
   public send(anchor: string, data: any): void {

src/app/wsmessage.ts

@@ -1,4 +1,4 @@
-export class WSMessage {
+export class WSMessage<T> {
   anchor: string;
-  data: any;  // TODO: sane annotation
+  data: T;  // TODO: sane annotation
 }