Anyone who has ever used Gmail, Microsoft Outlook Web Access or Google Maps is already indirectly familiar with the power behind AJAX, which gives the responsiveness associated with desktop applications to website applications. AJAX, which stands for Asynchronous JavaScript + XML enables back-channel communication in these web applications so that only small portions actually ever need to update in order to respond to the activity by users. AJAX is capable of offering an improved user experience, benefiting both the website designers with reduced server and bandwidth requirements, and the web application's users with increased usability.

The Yahoo User Interface, or YUI, is a library, or a set of utilities and controls that is written in JavaScript. The Yahoo! User Interface can be used to build web applications that are richly interactive through the use of DOM scripting, AJAX, DHTML and other effective tools. You will also find several core CSS resources in the YUI library. The YUI library's components are all open source, which means that they are free for any and all uses.

DOJO is an open source toolkit for DHTML that is written in JavaScript. DOJO builds on several different contributed code bases, including Burstlib, F(m) and nWidgets. For this reason, Dojo is often referred to as a unified toolkit. The main purpose of Dojo is to solve some of the long-standing problems that have existed relating to DHTML, which have prevented the mass development of dynamic web applications. Dojo makes it easy to build dynamic capabilities directly into web pages or other JavaScript supported environments. The components that are provided by Dojo can be used to create websites that are more responsive, user friendly and functional. Through the use of Dojo, users can build user interfaces more quickly and easily before, simplifying complex scripts through the use of lower-level Dojo APIs and compatibility layers.

Ext JS is a client-side JavaScript-based framework that can be utilized to build web applications. Ext originated as a set of extension utilities created for the Yahoo! User Interface library (YUI). These extensions were well received and quickly organized into their own independent library. Ext was originally distributed as Yui-EXT. Jack Slocum released version .33 of Yui-EXT, which turned out to be the final version of the code under that specific name, because by the end of the year the library had gained enough popularity that its name simply became Ext. In 2007, a company was formed to deal with the growing popularity of Ext, and the tool kit is now dual licensed under commercial license and the LGPL. On April 1, 2007, the Ext library officially hit version 1.0.

AJAX requires a significant level of mastery when it comes to JavaScript. Unfortunately, JavaScript happens to be one of the most misunderstood, misaligned programming languages out there. However, JavaScript is actually an extremely powerful object-oriented scripting language. As more developers become acquainted with the true power behind JavaScript, they can better take advantage of everything that AJAX has to offer the Internet.