Physics System with makr.js and p2.js

physics.js

function Physics(bodyConfs, shapeConfs) {
  this.body = bodyConfs;
  this.shape = shapeConfs;
}

function PhysicsSystem(gravity) {
  makr.IteratingSystem.call(this);
  this.registerComponent(ComponentRegister.get(Position));
  this.registerComponent(ComponentRegister.get(Rotation));
  this.registerComponent(ComponentRegister.get(Physics));

  this.world = new p2.World({
    gravity: gravity
  });
}

inherits(PhysicsSystem, makr.IteratingSystem, {
  onAdded: function(entity) {
    var physics = entity.get(ComponentRegister.get(Physics));
    var bodyConfs = physics.body;
    var shapeConfs = physics.shape;

    var body = new p2.Body(bodyConfs);
    body.id = entity.id;

    var shapeType = shapeConfs.type;
    // shapeType is of Circle, Plane, Rectangle, Convex, etc...
    var shape = new p2[shapeType](shapeConfs);
    body.addShape(shape);
    this.world.addBody(body);
  },
  process: function(entity, elapsed) {
    // Move physics bodies forward in tim
    this.world.step(1/60);

    var position = entity.get(ComponentRegister.get(PhysicsBody));
    var rotation = entity.get(ComponentRegister.get(Rotation));
    var body = this.world.getBodyById(entity.id);

    // Transfer positions of the physics objects to related components
    position.x = body.position[0];
    position.y = body.position[1];
    rotation.angle = body.angle;
  }
});