title: Contextual handling of RxJS Subject in Angular service
body: <p>I have a hot RxJS Observable that I want to respond to in different ways depending on the context of the application. The Subject emits a new event based on some global action intercepted by a directive, but then I want</p>
  
  <ul>
  <li>If a child component is subscribing to the Subject, then the child should handle the event</li>
  <li>Otherwise, use a global handler</li>
  </ul>
  
  <p>I can get the number of subscribers from the Subject and then tell the global handler to ignore if there are multiple subscribers, but it's not part of the API, so it seems like it may not be the right way to handle it. So what is the right way to do this?</p>
  
  <p>Also, should the global event handler be part of the directive, the service, or should that be in a new component?</p>