// assign all needed box2d variables

 var b2Vec2 = Box2D.Common.Math.b2Vec2
   , b2AABB = Box2D.Collision.b2AABB
   , b2BodyDef = Box2D.Dynamics.b2BodyDef
   , b2Body = Box2D.Dynamics.b2Body
   , b2FixtureDef = Box2D.Dynamics.b2FixtureDef
   , b2Fixture = Box2D.Dynamics.b2Fixture
   , b2World = Box2D.Dynamics.b2World
   , b2MassData = Box2D.Collision.Shapes.b2MassData
   , b2PolygonShape = Box2D.Collision.Shapes.b2PolygonShape
   , b2CircleShape = Box2D.Collision.Shapes.b2CircleShape
   , b2DebugDraw = Box2D.Dynamics.b2DebugDraw
   , b2MouseJointDef = Box2D.Dynamics.Joints.b2MouseJointDef;



// create a new world object with a gravity vector and allow sleep with true
  
 world = new b2World(new b2Vec2(0, 1), true);



// set an update function 60 times per second

 window.setInterval(update, 1000 / 60);

 function update() {

   world.Step(1 / 60, 10, 10);   
   world.ClearForces();

 }