I discovered that shiffman‘s github has an updated version of the code used in his book that is rewritten to use javascript, rather than processing.  It also uses the new p5.js graphics library, which brings a very familiar processing feel to javascript.  The new sample code also has examples to use a javascript-ported verison of box2d.  This seems to be a great way to explore how to use the library for my own projects, even if I don’t really want to use p5.js.