title: ExtJS: Attach Ext events to component before it exists
body: <p>Let's say I have a component, and this component needs to add an event listener to a component that does NOT exist yet, but will. Let's say it needs to for the 'beforerender' event of this yet-to-be-created component.</p>
  
  <p>As it is right now, without knowing how to do this in ExtJS, I would do something like this:</p>
  
  <pre><code>var wait = setInterval(function() {
      var cmp = Ext.getCmp('myThing');
  
      if (cmp) {
          clearInterval(wait);
          cmp.on('beforerender', function() {
              // ... do something on render
          });
      }
  }, 20);
  </code></pre>
  
  <p>How would I do this in Ext?</p>