In my previous article entitled Explorer Ways to extend ASP.NET AJAX Client-side Function, we only, from the client side’s point of view, focused on adding the client-side functionalities and behaviors to the current ASP.NET AJAX framework. However, creating custom ASP.NET AJAX client-side components is a pretty intensive work in JavaScript. While some ASP.NET developers are able to write JavaScript code, others may not have a complete understanding of the language and may prefer to use server-side objects that can be manipulated using VB.NET or C#. On the other hand, because server-side controls can output both HTML and JavaScript, they are good candidates for use with ASP.NET AJAX client-side components. In this article we will explore ways to extend ASP.NET AJAX client-side function from the server side.