title: Convert String into an object instance name
body: <p>I'm trying to turn an string into an instance name.</p>
  
  <pre><code>stage.focus = ["box_"+[i+1]];
  </code></pre>
  
  <p>this gives me back = <code>box_2</code>;</p>
  
  <p>but I need it to be an object not a string.</p>
  
  <p>In as2 I could use eval. How do I do it in as3?</p>