The closest thing to a selfreflective approach seem to be jsfiddle, but i have a hard time to make it work with multiple js files? And it is not object oriented although selfreflective.
An objectoriented "smalltalk like' web scripteditor with a selfreflective wsiwyg interface would be nice have running in the browser. CSS is mainly interface as i get it, and i can't see a reason to code an interfact by hand?