title: Access first item of array using async pipe in Angular 2
body: <p>How to access the first item of an array when using async pipe?</p>
  
  <pre><code>&lt;nav-tabs
     [tabs]="(pageTabs$ | async)"
     [activeTab]="(pageTabs$ | async)[0]"&gt;
  &lt;/nav-tabs&gt;
  </code></pre>
  
  <p>I've tried <code>(pageTabs$ | async)[0]</code> but it didn't work.</p>