title: Is there an operator or provision in RxJS to call every time a function is called?
body: <p>I have a function className.doSomething() which returns an observable.I want to know the time when this function was called or subscribed.</p>
  
  <p>className.doSomething()
  :callAtSubscribe( "print current time") 
  :tap()
  :subscribe()</p>
  
  <p>Need something appropriate in place of callAtSubscribe. </p>