Box2D-LiteJS is a small 2D physics engine. It is a JavaScript port of Erin Catto's Box2D-Lite written in C. The original library was developed for the 2006 GDC Physics Tutorial. This is based on the original version of the larger Box2D library. The Lite version is more suitable for learning about game physics.

Erin Catto's original version @ https://github.com/erincatto/box2d-lite