2005 will definitely be remembered as the rise of AJAX – the new development technique that many believe will blur the line between web-based and desktop applications. This mystical acronym, authored by Adaptive Path in mid February, is a label for the rich, highly responsive and interactive interfaces of AJAX-enabled applications. It stands for “Asynchronous JavaScript + XML”.
Although we are just beginning to realize its full potential, the proven success of famous AJAX-based projects like Google Maps signifies that this is not just another media hype, but rather a promising technology that may change web-applications as we know them.
The purpose of this article is to help developers understand the core concept of AJAX, realize its benefits and suitable application scenarios, and of course, become aware of its drawbacks.
You will learn about some of the most important AJAX implementations as well as about some of the leading development tools and components, which can help you jump-start your AJAX-enabled applications.
This document is aimed at ASP.NET developers, although anyone with a good knowledge of how the Internet works will gain a solid understanding of AJAX and its benefits.
The pursuit of a development technique like AJAX came from the need for making web applications much more usable and eliminating their key disadvantages in comparison with the desktop platform:
• Poor Interactivity – web applications require that users wait for full page reloads after each interaction with the server. During the loading time they have to stare at a blank screen, which tremendously disturbs the whole experience. Although broadband internet connections are becoming a standard, web applications are also becoming increasingly complex and "heavy" so the overall waiting time remains relatively the same.
• Unresponsiveness – classic web applications transfer the complete form data to the server, which in turn renders and sends back the full HTML markup of the page to the browser. This happens during each postback and in most cases is highly inefficient, since only a small part of the interface is actually changed. However, lots of bandwidth is consumed and the performance is significantly hindered. This leaves users with the idea that web applications are slow by nature. Even worse, the user will often find the page has scrolled to a different position, causing disorientation.
• Simplistic Interfaces – the requirement for full page postback whenever the user interface has to be changed imposes hefty limitations on the degree of sophistication of web user interfaces. Rich and smooth interfaces with on-demand update could only be implemented using Flash technology. This approach, however, is impractical for general use since it is very complex and requires a much different set of skills than those possessed by the typical web developer. It can also cause end-user issues as a plug-in is often required.
• Low Usability – if a web application reloads the whole page because the user made a new selection on a form, they will get confused. It is often the case that web applications work in a confusing and esoteric way because the web application has been built around the standard, simple view of the Internet protocols. ASP.NET meant we could build applications with more functionality more quickly, usability has a way to go yet.
AJAX was born with the idea to change all this and narrow the functional gap between the desktop and the web. The new generation of AJAX-enabled applications delivers close-to-instantaneous performance, rich interfaces and tremendously improved user experience. It opens new horizons for much closer interaction with the application and demonstrates in practice what was until recently considered impossible:
• Real-time map panning in Google Maps and Virtual Earth is just like image panning in Adobe® Photoshop®
• Folder browsing, message previewing, etc. in Microsoft® Outlook® Web Access is identical to that in the desktop version of Outlook.
• Validation checking on complex input fields can be performed by the server, without reloading the page.
• Virtual scrolling of huge tables with telerik r.a.d.grid is as fast as in Microsoft Excel®
What's interesting to know is that AJAX is not actually that new as a technology. It has been first used after Microsoft implemented Microsoft.XMLHTTP COM object that was part of The Microsoft® XML Parser distributive. As an ActiveX object in Internet Explorer 5, it was used to create the famous Outlook Web Access. You have probably seen AJAX in action for quite long in the MSDN Documentation treeview navigation. What is new actually is the name AJAX, which was widely accepted in 2005. Other labels for the same technology are Load on Demand, Asynchronous Requests, Callbacks, Out-of-band Calls, etc.
What's even more interesting is that AJAX is actually not a technology. It is more like a development technique that utilizes in a unique way a number of already mature technologies: HTML/XHTML, XML, DHTML, the XmlHttpRequest object, and JavaScript. For the purposes of simplicity we will refer to it as technology as it is widely accepted as such and provides a useful language to discuss the characteristics of the significant trend it represents.
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