// create a wall
var leftWall = Ti.UI.createView({
	backgroundColor:'#fff',
	width:2,
	height:200,
	bottom:0,
	left:0
});

world.addBody(leftWall, {
	density:12.0,
	friction:0.3,
	restitution:0.4,
	type:'static'
});

http://lancespellman.com/2011/12/20/cool-box2d-stuff-with-appcelerator-titanium/

This example adds a wall to keep the ball from rolling into space

Titanium Appcelerator Box2d simple example part 4

JavaScript