RadImageButton provides a flexible client-side API. You can easily interact with the button in the browser using the RadImageButton client-side object. In addition to a variety of client-side events, the client-side object model lets you achieve complicated tasks while avoiding unnecessary post-backs.
var button = $find("<%= RadImageButton1.ClientID %>");
var button = $telerik.findImageButton("<%= RadImageButton1.ClientID %>");