If you are intested in Generative Art, you are certainly aware of Processing.

RapydBox is such a tool, but it uses RapydScript (a Python like language) instead of Javascript.

RapydBox is entirely bases on Canvas JS

You can give a try here : RapydBox

For now, the browsers which seem to work the bests are Safari and Firefox. I will try to create a standalone application, to get rid of browsers incompatibilities