title: Extending Angular 2 ngModel directive to use observables
body: <p>Angular 2 <code>ngModel</code> directive works with variables and functions like</p>
  <pre class="lang-html prettyprint-override"><code>&lt;input [ngModel]=&quot;myVar&quot; (ngModelChange)=&quot;myFunc($event)&quot; /&gt;
  </code></pre>
  <p>Instead of variables and functions, I would like to use BehaviorSubjects instead</p>
  <pre class="lang-html prettyprint-override"><code>&lt;input [ngModel]=&quot;mySubject | async&quot; (ngModelChange)=&quot;mySubject.next($event)&quot; /&gt;
  </code></pre>
  <p>Is there a safe way to extend ngModel or use some kind of macro to reduce repetition in my templates?</p>
  <pre class="lang-html prettyprint-override"><code>&lt;input [myNewNgModel]=&quot;mySubject&quot; /&gt;
  </code></pre>