There are already quite a few JS libraries that support graph-related things. If I were approaching this as as development project, I would probably pick one and if it didn't do what I want it to do simply fix it.
But my goal here is to learn things the hard way, by coding them up. The intent is to have a number of accompanying modules for this one (which is just about the basic infrastructure) that support various aspects of graphs that I'm interested in.
If it turns out to be generally useful, great. But the goal is to pick up some fu in this domain.