How is setTimeout implemented in the javascript interpreters or timers in general?

Question

How is a function called after a time has passed implemented in javascript or any other interpreted language?

In other words, is there a loop behind in the javascript interpreter that checks all the time a list of timers, or is there any particular way that the operating systems handle this?

Thanks

Answer 1

There's a good description in the John Resig's blog

Answer 2

You could look at the source of Firefox or WebKit to see how they implemented it.