Programming ASP.NET 3.5, 4th Edition

AJAX

It may come as somewhat of a surprise that in a world where the emphasis seemed to have been squarely on writing neat and good server-side code to improve the interaction between website and user, the current revolution starts on the client side. The proliferation of the group of technologies most commonly known as Asynchronous JavaScript and XML, or AJAX for short, has been rapid and its reliance on only open standards has meant that competition for the best use of AJAX has been seen across all web platforms. Its cross-browser, cross-platform nature continues to ensure that.

Whether you use it to implement the more blatantly apparent UI features, such as the instant lookups of Google Suggest, or the subtler features, such as text box watermarking and the invisible updating of selection lists based on the contents selected in others, AJAX is here to stay despite the security risks that it exposes. After the initial commotion in 2005, and the development of several free server-side AJAX libraries such as Anthem.NET and MagicAjax.NET, many asked when Microsoft would come up with its own AJAX implementation.

Tip

If you’re interested in reading about some of the security risks of AJAX, have a look at http://www.cgisecurity.com/ajax/.

In January 2007, Microsoft answered with three distinct downloads for ASP.NET 2.0 and VS2005:

ASP.NET 2.0 AJAX Extensions 1.0

A library of client-side scripts and a half dozen core controls to place onto an ASP.NET page that render into an appropriate client-side script to enable AJAX functionality.

ASP.NET AJAX Control Toolkit

A library of almost three dozen server-side controls which demonstrate how to use and extend ASP.NET AJAX 1.0. This toolkit is under constant development at http://www.codeplex.com/AjaxControlToolkit.

ASP.NET AJAX Futures/ASP.NET 3.5 Extensions

Early developer releases of ASP.NET AJAX 2.0 for those who want to see how it is likely to develop. This product changes often and rapidly and is a good indicator of how other technologies Microsoft is working on will affect web developers. In late 2007, this package was wrapped into and is now part of the ASP.NET 3.5 Extensions preview package. It is likely, though, that another Futures package will appear once the 3.5 Extensions download comes out of beta.

As part of the OpenAjax Alliance, Microsoft has made the source code for the controls in the core Extensions download and the script library they render freely available under its shared source license to ensure interoperability across browsers, operating systems, and other AJAX libraries.

Visual Studio 2008 (VS2008) incorporates support for ASP.NET AJAX-enabled websites out of the box thanks to the inclusion of the .NET Framework 3.5.