title: ngrx - conditionally stop/remove Effect/Action
body: <p>I am currently building an application with Ionic2 and ngrx and I am trying to stop certian Actions if there is no network connection.</p>
  
  <p>With stop I mean to somehow make them invisible for other Effects and the store or stop them from further "propagating".</p>
  
  <p>Is there a way to do something like this?</p>
  
  <pre><code>@Effect()
  checkNetworkConnection$ = this.actions$
    .ofType(book.ActionTypes.LOAD_BOOKS, book.ActionTypes.CREATE_BOOK)
    .if(Network.connection === 'none')
    .do(() =&gt; new ShowNetworkAlertAction()) //Returns ShowNetworkAlertAction
    .stopPropagation(); // Removes the Action from the stream
  </code></pre>
  
  <p><code>stopPropagation()</code> should somehow "remove" the Action from the stream, after that it should be like if the action has never been dispatched. Even the store should not change anything or execute the code that would be executed on this Action.</p>