Last time we covered the event queue method, an entirely client-side way of implementing a light-weight, multi-level undo. I mentioned a couple of caveats, including that it does not work in multi-user collaborations, and that it doesn’t work for time-sensitive actions like sending emails. I missed a significant caveat that one of my readers, Alexander Botero-Lowry, pointed out: That two tabs, pointed to the same page, could get out of sync. I wrote about how to solve that issue with cookies.

Website: http://humanized.com/weblog/2007/10/22/undo_with_ajax_2/