Before the MVC pattern I would include UX classes simply by including this at the top of the JS, before Ext.onReady:
Ext.Loader.setConfig({enabl
In my case (using ux/DataTip.js), with ext-4.2.1.883 and sencha cmd 4.0.2.67, I was able to use Ext.ux classes with the provided solution, using:
Ext.Loader.setPath('Ext.ux', 'extjs/examples/ux');
But the sencha app refresh complains, with:
[ERR] C2008: Requirement had no matching files (Ext.ux.DataTip)
Coping/linking extjs/examples/ux to extjs/src/ux solve my problem. The application works and sencha cmd is also able to keep track of things. With this copy/link operation, there is no need to use Ext.Loader.setPath. Just use the class in the requires:
Ext.define('Demo.Application', {
name : 'Demo',
requires : [ (...), 'Ext.ux.DataTip'],