As I was playing around with a javascript physics engine called Box2dWeb. Almost immediately, I ran into an issue. I was receiving the error in Chrome console:

Uncaught ReferenceError: b2World is not defined

This occurs because the objects from this library have a "namespace". Well, actually, there are no namespaces in javascript, but the methods are stored in different objects. To resolve this issue, all you have to do is make aliases for these methods, or in other words, make short local variables for the full methods.

var b2Vec2 = Box2D.Common.Math.b2Vec2,
    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;

The author actually recommends this in the documentation. The idea behind the author's suggestion is putting the variables into the scope of the function to improve speed so that the browser doesn't have to search all the scopes.