--world js var default_prefs boundingWalls true size width 100 height

--world.js
var default_prefs = { boundingWalls: true, size: { width: 100, height: 200}, default_player: {defaultSize: 0.01}};
module.exports = function make_world(preferences) {
	preferences = _.extend(default_prefs, preferences);
	var units = [];
	// bla-bla-bla
	
	var listeners = {};
	var trigger = function (eventType) {
		if (listeners[eventType]) {
			listeners[eventType].forEach(function (item) {
				item ? item() : 0;
			});
		}
	}
	
	
	var obj = {
		prefs: preferences
		make_player: function (opts) {
			var p = make_player.apply(this, [units.length, _.extend(preferences.default_player, opts)]);
			units.push(p);
			return p;
		},
		bind: function (eventType, listener) {
			if (!listeners[eventType]) {
				listeners[eventType] = [];
			}
			listeners[eventType].push(listener);
		},
		unbind: function (eventType, listener) {
			if (listeners[eventType]) {
				delete listeners[eventType][listeners[eventType].indexOf(listener)];
			}
		}
		
		// bla-bla-bla
	};
	return obj;
}

--player.js
module.exports = function make_player(id, preferences) {
	// bla-bla-bla
	var size = this.prefs.size.width * preferences.defaultSize;
	var that = {
		id: id,
		type: 'player',
		size: size
	}
	return that;
}