Is JavaScript single threaded? If not, how do I get synchronized access to shared data?

Question

I have a web page with DIVs with a mouseover handler that is intended to show a pop-up information bubble. I don\'t want more than one info bubble

Answer 1

FYI: As of Firefox 3 there is a change pretty much relevant to this discussion: execution threads causing synchronous XMLHttpRequest requests get detached (this is why the interface doesn't freeze there during synchronous requests) and the execution continues. Upon synchronous request completion, its thread continues as well. They won't be executed at the same time, however relying on the assumption that single thread stops while a synchronous procedure (request) happening is not applicable any more.