JQuery code that displays elements in the center of the screen

(function($){
$. = function(){
var top = ($(window).height() - ())/2;
var left = ($(window).width() - ())/2;
var scrollTop = $(document).scrollTop();
var scrollLeft = $(document).scrollLeft();
return ( { position : 'absolute', 'top' : top + scrollTop, left : left + scrollLeft } ).show();
}
})(jQuery)