Random con Query en mongoose Nodejs

query.ramdom.js

module.exports = exports = function (mongo){

	var mng = mongo || require('mongoose');
	var Query = mng.Query;

	Query.prototype.random = function ( query, func ){
		var q = typeof query === 'object' ? query : this.query;
		var f = typeof query === 'function' ? query : func;
		if(!( typeof f === 'function' )) retrun new Error("Is not a function");
		this.count(q, function (err, count) {
			if( err || count =< 0 ) return f( err || new Error("Query is 0"), null);
			this.findOne(q).skip( Math.floor(Math.random() * count) ).exec(f);
		});
	};

	mng.Query = Query;

	if( !mongo ) return mng;
};