Hot skills: Ajax Ajax is Microsoft's free framework for creating Ajax (Asynchronous Javascript and XML) web applications

What is it? Ajax is Microsoft's free framework for creating Ajax (Asynchronous Javascript and XML) web applications. At its simplest, it lets ASP developers do this - or add Ajax controls to their existing applications - without leaving their familiar drag-and-drop environment, and without having to understand Javascript or asynchronous communication with the host. According to the O'Reilly Network, it protects developers from "the underlying gibberish that makes it [Ajax] all work".

Ajax applications can have the kind of rich user interfaces normally associated with desktop applications. They are also more responsive, because instead of reloading the whole page when the user makes a change or a request, they exchange the minimum possible data with the server while the application remains available to the user.

While providing undoubted performance benefits, this violates a number of rules and safeguards -it "breaks" the back button which enables you to return to the unmodified page, and means the URL no longer identifies a single, unique state of a page. Ajax is supported by Visual Studio 2008, supplied as part of 3.5, and can be downloaded for 2.0.

Where did it originate? Ajax began with the codename Atlas. It was released as a separate download early in 2007, then included with .net Framework 3.5, released at the same time as Visual Studio 2008 at the end of last year.

What's it for? Ajax supports server-side programming, client-side programming or a combination of both. Developers can add partial update functionality to existing applications by wrapping sections of their websites in the Ajax server control 'update panel', which enables the server controls to update without a post-back.

Those with a knowledge of Javascript can build client-side applications using the client-side Ajax framework, which is also shipped in a standalone version as the Microsoft Ajax Library. According to Microsoft's official site, this framework can be used with other server-side technologies - such as PHP and ColdFusion - because it is not tightly coupled with

There are alternatives to Microsoft's Ajax offering for ASP.Net. Gaia Ajax Widgets for .net is a commercial library of Ajax modules, some of which are also available in open source form. Professional, a widely used, independently developed, free library for which pre-dated Microsoft's support for Ajax, now appears to have been abandoned.

What makes it special? Ajax builds on generally available Microsoft skills - for example, Javascript debugging using Visual Studio 2008. Developers can also explore the possibilities of using other .net-supported languages as alternatives to Javascript.

How difficult is it to master?

Developers who want to move beyond using the supplied Ajax controls will have to get to grips with Javascript and D/X/HTML, and understand the XMLHttpRequest API.

What systems does it run on?

Microsoft says Ajax supports all popular browsers (although not yet mobile devices). However, there may be compatibility issues because of different browsers' document object models, and the way they implement Javascript.

Rates of pay developers with Ajax £25,000 -£40,000.

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