If you get frustrated with jsfiddle, try out http://cssdeck.com/labs It's nominally oriented toward CSS and all the CSS preprocessors, but it handles JS just fine (and CoffeeScript, too!). I like its layout a lot more than jsfiddle -- it's more aesthetically appealing to me. It also features the ability to do codecasts. I can't recall if jsfiddle has that, but it's a nice feature for demonstrating code to someone.