New Ajax laundry detergent is stronger than dirt.

You may have seen a lot of AJAX floating around on the web recently. No it isn't because everybody has a lot of dirty clothes to wash. This is the new AJAX. Asynchronous Javascript And XML. Although it isn't really anything new, it's a new way of writing some web applications. 

Basically, Ajax makes use of the ability of Javascript to fetch a URL. Instead of loading a page or an image however, the modern way of doing things is to talk XML with a server. If you recall, I've previously mentioned the new wave of XML-RPC applications taking over the world. Ajax is a big part of that.

The best example of why somebody might want Ajax is to envision a web page with 'auto-complete as you type' information.  As you start typing something, it starts to show you results based on what you've typed so far. To do this in a traditional web page or even a Javascript page, you need to have all of the data loaded before you can search through it for the relevant piece. This could be thousands of entries. With Ajax, as you type, the browser is actually doing web requests behind the scenes to match the data - and showing you the results without having to reload or go to another webpage.

This is one step closer to having web pages be as interactive and full-featured as native applications (i.e. .exe files).

The downside of all this is that things are going on behind the scenes, and this could be disconcerting. Privacy issues, usability issues (the back button might not go back to where you thought). But perhaps the biggest issue of all is that of dealing with software bugs. When software is happening invisibly behind the scenes and doesn't perform the expected result, it's very difficult to troubleshoot. The person reporting the bug might not even know that something is happening behind the scenes. As far as they're concerned, they loaded a web page from foo.com and the web page didn't work. It might not have been foo.com's page at all. It might have been a server in Vermont that was providing an XML feed and experienced a brief outage. Somebody from foo.com however is going to have to spend hours figuring this out.