Get the Box2D source code, run the following:

1:git submodule init
2:git submodule update
3:cd box2d
4:git checkout -b branches/tags v2.4.1
5:cd ..

Building

In order to build box2d.js yourself, you will need Emscripten and cmake.

For more information about setting up Emscripten, see the getting started guide.

To configure and build box2d into the build directory, run the following: build.bat