center an element with jQuery

function elementCenter(id){
    var obj = $("#"+id);
    obj.css("position","absolute");
    obj.css("top", Math.max(0, (($(window).height() - obj.outerHeight()) / 2) + $(window).scrollTop()) + "px");
    obj.css("left", Math.max(0, (($(window).width() - obj.outerWidth()) / 2) + $(window).scrollLeft()) + "px");
}