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

It is single threaded in browsers. Event handlers are running asynchroniously in one thread, non blocking doesn't allways mean multithreaded. Is one of your divs a child of the other? Because events spread like bubbles in the dom tree from child to parent.