code: function uuid4() {
  	  var d = now();
  	  var uuid = 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function(c) {
  	    var r = (d + Math.random() * 16) % 16 | 0;
  	    d = Math.floor(d / 16);
  	    return (c === 'x' ? r : (r & 0x7 | 0x8)).toString(16);
  	  });
  	  return uuid;
  	}
docs: from http://stackoverflow.com/a/8809472/1138191