You could look at something like Processing.js:
http://processingjs.org/exhibition
UPDATE:
If you want a game API, I haven't tried it, but the comments are promising, you can look at:
http://ajaxian.com/archives/gamejs-canvas-game-library
In order to keep the javascript small and optimized I tend to just access the elements directly, but, over time people will create libraries of their own, but it may not be libraries that are useful in certain situations.
UPDATE 2:
Looks like you can get a version of gamejs from here:
http://tommysmind.com/gamejs/GameJS-0.1.rar
This also was an interesting article on GameJS by the author:
http://tommysmind.com/gamejs/