ASP.NET AJAX callbacks to Web Methods in ASPX pages

http://geekswithblogs.net/frankw/archive/2008/03/13/asp.net-ajax-callbacks-to-web-methods-in-aspx-pages.aspx

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Making ASP.NET AJAX calls to web services has become increasingly popular these days. This approach not only provides a good separation of concerns but also makes it possible to create a truly ajax'ed web site with JavaScript's power on the client side. However, you may in some situations want to move one or more web methods to ASPX pages. You often have methods that are logically dedicated to specific ASPX pages, and you don't really want them to be exposed to the public through the ASMX file. Generally, this is the most appealing reason why you want to place web methods in ASPX pages.

Both ASP.NET AJAX Extensions and ASP.NET 3.5 support AJAX callbacks to the web methods placed in ASPX pages. It only requires a few simple steps to do this. For example, you want to move a web method called GetProducts to an page named Products.aspx, and you want to invoke the GetProducts method directly from JavaScript. The first step is expose GetProducts as a web method.