AJAX :: How To Inherit From An Exisiting Controls

Is there any normal way how to extend existing ajax control?Situation: I have 1 ajax control named AjaxControl1 that has AjaxControl1.js to define javascripts. There is string property Value1 accessible from client.Now i need create new ajax control named AjaxControl2 inherited from AjaxControl1. all server and client functiouns are same plus i need add string property Value2 accessible from client too. but i dont want create copy of AjaxControl1.js and add some new rows, but use existing javascript file AjaxControl1.js and somehow extend from it to get access Value2 from client.Point is what if i change something in AjaxControl1, i want that change in AjaxControl2 too but without change in AjaxControl2 or AjaxControl2.js