As a non-JavaScript developer, I'm curious as to where the "magic" (things that aren't intuitive to implement) is.

The algorithm for drawing an edge between nodes, for instance, doesn't seem magical (just a spline or beizer curve) - but only because the library doesn't care about routing edges around nodes. Layout isn't magical because you're doing it manually - unlike graphviz/xdot, for instance.

Does this library have magic, or is it, instead, the product of a lot of elbow-grease?

If it was the latter, I'm not going to complain - I'll take a pre-written library over doing it myself in a heartbeat - but, as I'm not a web developer, I wonder if I'm missing something, and it's interesting for me to taxonomize things.