Extend ui5 control with method interface

HI

I need to extend SAPUI5 control and I've the following example (Thanks to Dennis!),Currently there is extend for

Autocomplete which is working fine but now I need that that the new control will also have the ability to extend method which he getting from some additional interface control(lets say I've one interface control with method's and I need that all my controls will extend it like the control in the example)

e.g. to return if isRoot is true or false ,How it can be done via UI5 ?

JS Bin - Collaborative JavaScript Debugging

p.s. I found this getInterface() there is a way to use that this can help?

JsDoc Report - SAP UI development Toolkit for HTML5 - API Reference - sap.ui.base.Object

Thanks in advance:)

Joerg