Q:

Interacting with box2D objects

How can I interact with an object in box2d, I'm completely new to this so I have no clue what to do. The box is created like this:
bodyDef.type = b2Body.b2_dynamicBody;
fixDef.shape = new b2PolygonShape;

fixDef.shape.SetAsBox(0.5, 0.5); // Half-Width, Half-Height

bodyDef.position.x =  5;
bodyDef.position.y =  5;
world.CreateBody(bodyDef).CreateFixture(fixDef);

How can I change the x, y positions of that box, tried bodyDef.position.x--; but it returned "bodyDef is not defined". How do I access this?

A:

For moving here is SetTransform, for interacting MouseJoint. BodyDef is used to make creation of bodies easier, so it is used just in that function, you have to store value returned by CreateBody, and read documentation first.

