title: angular2 correct way to have service call member function of Component
body: <p>How should I let a service call method of a component (i am using typescript with Angular2)?</p>
  
  <p>My service need to occasionally notify components some events. (update them randomly over time)</p>
  
  <p>One way I could think of is to let the service keep a ref to the component and call component's method directly using the ref.</p>
  
  <p>Is there other better/proper way to do it in Angular2?</p>
  
  <p>Thanks</p>