If you want to show off how simple your API is then I can think of several things that would improve clarity:

1. Don't use parentheses in comments. They make things more visually confusing when javascript imposes enough syntactic clutter as it is.

2. What's with /* */ ? Doesn't js allow keyword arguments?

3. Your method names are probably a little short for my taste. I'd be happier with sequence() and parallel() instead of seq() and par(). Par especially seems a little too obscure when first encountering it.

4. "cx = location | cr = radius" - why not allow both forms? - or just the clearer one rather than the shorter one.