All about Ajax!

[eluser]Nick Husher[/eluser]
It depends on our audience; if you're building for a very broad audience (impared users, users operating from behind strict corporate firewalls, the paranoid linux dorks, and grandmas running Netscape 4.1), you should be eating and drinking progressive enhancement. If 98% is good enough for you, go the Facebook route.

I'm of the opinion, by the way, that Facebook can largely get away with forcing their users to use JS because their user base trends toward the young, who tend to be both tech-savvy and tend to be fairly casual with the potential security risks involved with web technologies. Users who know what javascript is, and have a problem with it, wouldn't be interested in having a Facebook presence anyway.

It’s also a good idea not to add AJAX stuff to an element that doesn’t have a click event natively. Things like divs, h1s and spans arn’t clickable, and thus arn’t clickable by programs like screen readers.

I disagree: WAI-ARIA indicates that an appropriate role attribute should be sufficient to trigger screen readers. Then it's up to you to write the necessary keyboard navigation. As a shameless plug for my favorite JS library, YUI now has plugins that make many of its widgets WAI-ARIA-complaint, which if you're into that kind of thing, is a huge amount of work done for you, right out of the box.

The way I've been doing it lately is to develop one or more modules (in YUI, but other libraries have similar design patterns) and load them all in as I need them with the YUILoader function, which inserts them into the DOM tree after the basic document has finished downloading. The advantages of this is that it immediately displays the document information to the user while deferring complex and time-expensive UI loading. You can do some basic javascript style manipulation to show controls as they've finished loading and update the user on the progress of the enhanced UI effects.

The disadvantages of this are an increased code overhead--I have to load the loader and define my modules to insert the code on the page--and a longer lag time before enhanced controls become active.