Question: Anybody knows a Editor where i can develop my JS directly in the Browser with a js based Editor? 

It would be nice if the code completion is customizable so that you can add own objects and methods, possibly documentation for each method / object.
Code completion is not required for the objects that come with javascript (like window) as we're using Mozilla's JS Framework Rhino.

Thanks in advance

Best Regards
Flexo

Answer: 
[JsFiddle](http://jsfiddle.net) is used in a lot of examples on this site (no code completion).
I just stumbled across a JavaScript implementation of vi. But that doesn't do autocompletion.

[this one](http://ajaxian.com/archives/byteplug-experimental-online-javascript-editor) claims to do so, though. I know nothing else about it, though.