Ext JS 4 introduces a new package organization and that is why some class names are not the same as they were in Ext JS 3.
When we start migrating an application from Ext JS 3 to Ext JS 4, it can get a little confusing, because some class names are different. The classes in Ext JS 4 that have changed from Ext JS 3 contain a property called
alternateClassName, which indicates that the Ext JS 3 class names are compatible with Ext JS 4. You can still use Ext JS 3 class names when implementing an Ext JS 4 application, but it is recommended that you use the new class names.
This appendix lists all the Ext JS 4 classes that have a name compatible with Ext JS 3 classes.
Some of Ext JS 4 classes can have more ...