title: Observable.onSubscribe equivalent in RxJs
body: <p>In RxJava, there is <a href="http://reactivex.io/RxJava/javadoc/rx/Observable.OnSubscribe.html" rel="noreferrer">Observable.OnSubscribe</a> which will call your action when something subscribes to the observable.  </p>
  
  <p>Is there an equivalent in RxJs?</p>
  
  <hr>
  
  <p><em>It seems as though they've taken the page down since asking this question.  Google's cached version <a href="http://webcache.googleusercontent.com/search?q=cache:VddYHdNcPaUJ:reactivex.io/RxJava/javadoc/rx/Observable.OnSubscribe.html%20&amp;cd=1&amp;hl=en&amp;ct=clnk&amp;gl=us" rel="noreferrer">lives here</a>.</em></p>