I wrote a little bit about installing swank-js a couple of posts up. You can also check out all my emacs-settings on github https://github.com/magnars/.emacs.d/blob/master/setup-slime-...

The only thing missing there is the packages installed through package.el, which would be slime-js in this case.

And here's the code for the bouncing ball: https://github.com/magnars/blockout