The major defining characteristic, though, is the asynchronous aspect of the technology. Even XML is in there by coincidence; people describe things as “AJAX” applications when they don’t use XML at all. There is no new language or file format here. There’s no specification; no definition of what AJAX is or is not. There are no special tools. There’s no visual appearance that could be created except what you could do with a web browser, HTML, JavaScript, and CSS anyway. In fact, if you were allowed to stub out the data, you could write any AJAX application with only those basic client-side web technologies.

AJAX is typically a generic JavaScript program to allow thin clients to do field validation (by asking the server) without refreshing the entire page. Google uses it for maps. It works by sending standard HTTP queries to the server. Your application specific code all lives on the server.

The AJAX-like approach has three main advantages over Applets.

1. JavaScript generally starts faster than an Applet. The browser preloads the JavaScript run time, but delays loading the Applet JVM until first use. The load overhead for JavaScript gets buried in the browser start up time, when the JVM load gets blamed on the first Applet. The JVM is a much bigger and more complex animal than the JavaScript runtime.
2. AJAX is really just HTML and JavaScript and CSS, so it acts like a web browser. That is, you can resize the window and expect to see text and tables wrapped and presented in all the normal ways. All the UI kludginess of Applets is gone.
3. JavaScript is not constrained by the same tight sandbox restrictions as Java. Your users don’t have to deal with the geekiness of signed Applet permission granting.

• Java is object oriented. It won’t fall apart under its own weight as project complexity grows.
• JavaScript has many bugs and platform-specific eccentricities.
• JavaScript might be looked on as a limited or toy language designed for scripting inside a browser. Java is a general purpose language suited for pretty well any sort of computation.
• Java security is tighter. Unsigned Applets are less potentially dangeous. Sooner or later after a major scare, corporate America is going to ban JavaScript from their machines because of security risks. At that point, all legitimate Ajax code will stop working, so I consider it irresponsible to go the Ajax route.

Books

	recommend book⇒Pragmatic Ajax, A Web 2.0 Primer
		paperback
	ISBN13:	978-0-9766940-8-3
	ISBN10:	0-9766940-8-5
	publisher:	Pragmatic Bookshelf
	published:	2006-04-10
	by:	Pragmatic Bookshelf
Covers Ajax with Java, .NET, and Ruby on Rails server frameworks.
amazon.ca amazon.com chapters.indigo.ca powells.com amazon.fr barnesandnoble.com amazon.de amazon.co.uk