Ajax Mistakes

Ajax is an awesome technology that is driving a new generation of web apps, from maps.google.com to colr.org to backpackit.com. But Ajax is also a dangerous technology for web developers, its power introduces a huge amount of UI problems as well as server side state problems and server load problems.

I've compiled a list of the many mistakes developers using Ajax often make. Javascript itself is a dangerous UI technology, but I've tried to keep the list to problems particular to Ajax development:

Mistakes:
1. Not giving immediate visual cues for clicking widgets.
If something I'm clicking on is triggering Ajax actions, you have to give me a visual cue that something is going on. An example of this is GMail loading button that is in the top right. Whenever I do something in GMail, a little red box in the top right indicates that the page is loading, to make up for the fact that Ajax doesn't trigger the normal web UI for new page loading.

2. Breaking the back button
The back button is a great feature of standard web site user interfaces. Unfortunately, the back button doesn't mesh very well with Javascript. Keeping back button functionality is a major reason not to go with a pure Javascript web app." (Via Alex Bosworth)

And the list continues ...