I don't know why and obviously, this isn't true for everybody, but i'm always at war with CodeMirror. It auto-outdents and reformats things exactly how i do not want them. Whenever i'm forced to use CodeMirror, i'm undo-ing more than i'm typing and swearing about once every 5 seconds.
So, if you are one of those people, like me, that is always getting furious at jsFiddle, try an ACE based alternative.
Interestingly, once you realize that these code-editor components are quite simple to implement on a web-site, you also understand why there are 100+ jsFiddles clones. Most, if not all web-devs should be able to create one in half a day. They may think it's harder before they begin, but they will be pleasantly suprised.
This is likely also, why we're seeing a new "Online IDE" every week these days. GitHub's new Atom.io editor is the first one in a long time, to not use CodeMirror or ACE at its core.
What becomes interesting, though, is taking these ready-built components and trying to improve on the paradigm and the user experience.
With Plunker (which was originally inspired by jsFiddle and some of its short-comings) I've been trying to build tools around the core experience to make prototyping easier for the modern web developer.
Something that you won't find anywhere else is Plunker's package catalogue [1]. What is particularly unique about this is that it allows you to quickly find and 'insert' package dependencies into your markup in a way that resolves dependencies and in a version-aware fashion. These packages can be combinations of js and css. The web-based-IDE lets me take an approach that isn't viable for offline alternatives like bower and component but that is much easier from the user's perspective. A side-benefit of this approach is that all templates on Plunker can be made to auto-update to the latest (matching semver) version when they are opened or on-demand.
As I continue working on Plunker, this is the sort of feature that I hope will help it distinguish itself from the hordes of look-alike clones. Right now, I'm working on a new UI for the editor to allow a more flexible approach to editing files in a column/row grid [2].
I know there are browser extensions that allow Vim emulation, but those are generally more oriented toward controlling the browser, rather than using an editor.
The reason that you may not see this more often is that implementors of ACE may simply not expose the option.
[1]: http://ace.c9.io
I'm learning to code JS in my free time at work and I'm limited to using Chrome, so this suits my needs very well indeed.
