Problem extending existing dojo object about dojo-typescript HOT 1 CLOSED

/// <reference path="dijit.d.ts" />

import widget = module("dijit/_Widget");
import button = module("dijit/form/Button");  // I assume this module exports a class which extends Dijit._Widget (which contains definitions of the set/get/watch methods and more)

class dfButton extends button { 
                         _setDisabledAttr(value) 
                        { 
                                this.set('readonly', value);
                                this._set('disabled', value);
                        }

                        _getDisabledAttr()
                        { 
                                return this.get('readonly');
                        }
}

export = dfButton;