title: Getting event if connected in RxJs WebSocketSubject
body: <p>I wonder how can i get the response, if the <code>WebSocketSubject</code> is connected? </p>
  
  <p>In the source code (<a href="https://github.com/ReactiveX/rxjs/blob/master/src/observable/dom/WebSocketSubject.ts" rel="nofollow noreferrer">https://github.com/ReactiveX/rxjs/blob/master/src/observable/dom/WebSocketSubject.ts</a>) they have a <code>openObserver</code> member of type <code>NextObserver&lt;Event&gt;</code></p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code> socket.onopen = (e: Event) =&gt; {
        const openObserver = this.openObserver;
        if (openObserver) {
          openObserver.next(e);
        }
        .....</code></pre>
  </div>
  </div>
  </p>
  
  <p>How can i connect to it, to get the event, that the socket was opened?</p>