The story of software development in the last few years has been driven by the need to provide a good user experience without installation issues and update woes. For some people that has meant building "smart client" applications, as promoted by Microsoft. For others, that has meant building rich Internet applications (RIAs) using technologies such as AJAX, Microsoft Silverlight, and Adobe Flash and Flex. For a sizable subset of Web applications, "zero footprint" on the client is a requirement, which usually leads to the adoption of AJAX for these applications. (When we say AJAX, we include all the different varieties of asynchronous JavaScript Web applications, whether or not they use XML for their data exchange.)

Challenges for the AJAX Developer
The biggest problem with AJAX for developers is that it has been hard to implement, debug and maintain. In particular, an AJAX application is prone to Web browser dependencies, and users tend to be headstrong about using the browser they currently favor rather than the browser that will best run the particular application they happen to be using. That leads developers to try to write AJAX applications that will run on any browser, or at least any major, current browser.

Browser compatibility issues can be a nightmare, and AJAX developers who have struggled to make their application run properly on their primary browser target are often ready to tear out their hair when they discover major problems running the same application on the other browsers they need to support. AJAX libraries and frameworks help somewhat, since one of their design goals is typically to isolate the application programmer from the different JavaScript implementations and Document Object Models (DOMs) of different browsers. Even so, the library developers have a hard time hiding all the incompatibilities, especially as new browsers (for example, Google Chrome) and browser versions (for example, Internet Explorer 8) keep coming out.

At a slightly higher level, data binding is often harder than it should be. Many AJAX applications are written to communicate with database servers. In an ideal world for the application programmer, there would be an easy, standard way of binding data streams to AJAX controls and controlling how much data is downloaded and when "dirty" data is written back to the database. As it is now, data binding is often pushed to server-based frameworks, and live AJAX data updates are often "left as an exercise for the student."

Where We Are Now
We developers are currently blessed with a plethora of AJAX libraries and frameworks with a wide range of approaches and prices ranging from completely free to thousands of dollars per year. Some are strictly JavaScript APIs. Some have XML tag libraries; some don't.

Some have tools that make them easier to use; most don't. Some have current, complete documentation. Some have books written about them. Some have videos explaining their use. Some are supported by vendors - typically for a non-negligible price. Some have an active community contributing to their development. Some have a pool of knowledgeable consultants who use the toolkit on a regular basis and are available to help with projects.