JSBin

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).

Funny enough, I went and put in `while (true) {}` and the right hand side did show an error about it running too long. But I clicked Save and was prompted to create an account (or "...I don't want to be awesome...") and I couldn't click the buttons. I open Activity Monitor and sure enough Chrome's Renderer is pegged at 100%. I killed the process but now whenever I open the /cs/new page (even in incognito amazingly) it pegs at 100%. I also had to kill the script in Firefox but when I refresh the pages it's okay. I guess while(true){} is always nasty.

I don't think the webworker solution would work for something like this, anything that needed to use anything outside of the workers context would break. It seems like khan's environment is much more restricted, so they can get away with it.

Any detailed explanation available about how this is implemented (other than by having to dig in the code...)?

I think jsFiddle is great! However, I haven't really tried any of the others. This one looks nice, and just at first glance one thing that I find really interesting is the built in console. I think the devs at jsFiddle should totally implement something like this. Probably the biggest reason I don't use jsFiddle more often is that after I build a demo, occasionally I will need to use the Chrome console to get at and inspect one of my objects or the like, and for whatever reason I can't get at the objects in my fiddle, the console never seems to work right. I will probably give this one a whirl instead the next time I want to use jsFiddle. If everything else is on par with jsFiddle and it has a good console with visibility of all my objects then I'll probably switch to it.

Does anyone know if there is a way to get the Chrome console to work right, ie. have visibility to all the variables, functions, etc that I create in my fiddle?

There is also CodePen ( http://codepen.io/ ), and dabblet ( http://dabblet.com/ ) now seems to have (alpha) javascript support, too; the more, the merrier :D

jsfiddle is SO much better. I respect Remy, but I just like the way jsfiddle is. I tried all of them out and I found that jsfiddle > jsbin > codepen > others. The panels are just more intuitive and it feels less constrained than the others.

I wonder why? It doesn't update result as you type, doesn't support Less, CofeeScript etc., doesn't have console and until recently it used ancient and broken version of codemirror.

Also http://jsconsole.com which also lets you connect to remote sessions (eg on a phone).