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.

As it is right now, without knowing how to do this in ExtJS, I would do something like this:

```
var wait = setInterval(function() {
    var cmp = Ext.getCmp('myThing');

    if (cmp) {
        clearInterval(wait);
        cmp.on('beforerender', function() {
            // ... do something on render
        });
    }
}, 20);

```

How would I do this in Ext?