title: Angular2: Watch an external variable outside of angular
body: <p>I want to be able to watch and update when a variable outside of angular2 changes. So let's say I have this in an external javascript file:</p>
  
  <pre><code>var test = 1;
  </code></pre>
  
  <p>How can I bind this variable to a property in a component?</p>
  
  <pre><code>@Component({
     ...
  })
  
  export class MyComponent {
      watchy = window.test;
  }
  </code></pre>
  
  <p>Apparently this should just work, according to <a href="https://stackoverflow.com/questions/34569094/what-is-the-angular2-equivalent-to-an-angularjs-watch">this answer.</a><br>
  But it doesn't. If I change the variable in the console, the variable does not update displayed in a template. Am I missing something?</p>