Is JavaScript guaranteed to be single-threaded?

Question

JavaScript is known to be single-threaded in all modern browser implementations, but is that specified in any standard or is it just by tradition? Is it totally safe to assu

Answer 1

I've tried @bobince's example with a slight modifications:

    


    
    

    Run
    

So, when you press Run, close alert popup and do a "single thread", you should see something like this:

click begin
click end
result = 20, should be 20

But if you try to run this in Opera or Firefox stable on Windows and minimize/maximize window with alert popup on screen, then there will be something like this:

click begin
resize
click end
result = 15, should be 20

I don't want to say, that this is "multithreading", but some piece of code had executed in a wrong time with me not expecting this, and now I have a corrupted state. And better to know about this behavior.