I've been using OpenJSCAD (demo at http://openjscad.org/) for small parts and really like it. With some work it could probably do what you describe but as far as I can tell no one is using it that way.
It would be cool if there was an ecosystem of OpenJSCAD parts that you could import as javascript modules.
It would be cool if there was an ecosystem of OpenJSCAD parts that you could import as javascript modules.