title: Search for an item in MixedCollection
body: <p>I use Ext JS, so</p>
  
  <p>I have a toolbar with items (buttons, labels etc). I add elements to the toolbar like this :</p>
  
  <pre><code>toolbar.add(this.tempObject);
  </code></pre>
  
  <p>or like this:</p>
  
  <pre><code>toolbar.add({
      xtype: button,
      ...
  });
  </code></pre>
  
  <p>So, I want to find some elements in this toolbar by field <code>"ref"</code>. I tried to:</p>
  
  <pre><code>toolbar.items.find(new Function("there should be my function, but i have no idea how to write it"));
  </code></pre>
  
  <p>And there is no promice that every element in this collection will have this field. </p>