[AndrewStephens]

I've messed around with various incarnations of Box2D, including at least one other Javascript port. How does this one compare performance-wise? Does doing a full rewrite perform better than the automatically generated Javascript of the other ports?

[shakiba]

The main difference is that it is a hand-made rewrite, so the code is readable and improvable, so performance can be improved and optimized even if it is not fast enough in some cases. Also see my other comment about comparison with emscripten port.