Ajax (also AJAX; /ˈæks/; an acronym for Asynchronous JavaScript and XML)[1] is a group of interrelated web development techniques used on the client-side to create asynchronous web applications. With Ajax, web applications can send data to, and retrieve data from, a server asynchronously (in the background) without interfering with the display and behavior of the existing page. Data can be retrieved using the XMLHttpRequest object. Despite the name, the use of XML is not required (JSON is often used instead), and the requests do not need to be asynchronous.[2]

Ajax is not a single technology, but a group of technologies. HTML and CSS can be used in combination to mark up and style information. The DOM is accessed with JavaScript to dynamically display, and allow the user to interact with, the information presented. JavaScript and the XMLHttpRequest object provide a method for exchanging data asynchronously between browser and server to avoid full page reloads.

The Document Object Model (DOM) is a cross-platform and language-independent convention for representing and interacting with objects in HTML, XHTML and XML documents.[1] Objects in the DOM tree may be addressed and manipulated by using methods on the objects. The public interface of a DOM is specified in its application programming interface (API). The history of the Document Object Model is intertwined with the history of the “browser wars” of the late 1990s between Netscape Navigator and Microsoft Internet Explorer, as well as with that of JavaScript and JScript, the first scripting languages to be widely implemented in the layout engines of web browsers.

Dojo or jQuery, quick answer

  • JQuery if you are new to javascript/web programming and only want to jazz up your pages a little. Also, if your project is only a few months and/or only a few hundred lines, pick JQuery. It will get you there faster.
  • Dojo if you have a large project and can spend time on a very steep learning curve and want to be able to create and re-use widgets, data connections and whatnot.

This answer do not take into account the “fun factor”. If your aim is to have fun JQuery will give you a quick fix but Dojo will be more rewarding in the long run.