I considered it - there was a point where I thought "Wouldn't it be cool if I implemented Cheney-on-the-MTA in JavaScript?" JavaScript doesn't have setjmp/longjmp, but it can be faked with exceptions. But I wasn't sure about the garbage-collection aspect, since you don't have the same fine-grained control over memory that you do in C, and I was afraid that just holding onto the continuation closure would accidentally capture the whole rest of the stack (because of arguments.caller), trading a stack overflow for a massive memory leak. And since I didn't want to spend too much time on the project, I decided to punt on the whole thing.
I think the setTimeout trampoline is better anyways - in addition to cleaning everything up, it also gives the browser's event loop a chance to run, so you don't risk locking up the browser.
