[remysharp]

It's been mentioned, but the Khan editor gets around the problem because its a close environment - and I can't run the code the user submits in to a worker easily.

The while problem has been raised before, and there is a tiny bit of protection (we parse the code line you're on, and if its a while loop, it's supposed to ignore live execution - though clearly that's not enough). It's true to say I'm still looking for a solution :)

That all said, you dont lose your work if you hit this kind of loop and it hangs the UI. The reason is two fold: 1) jsbin, since it was released in 2008 always saves code to localStorage, but more importantly, 2) it's saving your code to the server AS YOU TYPE - so you hit refresh, and you get you bin back (and the correct URL and saved in your history if you're signed in, etc).