Move Center with Jquery

$(document).ready(function() {
        jQuery.fn.centerScreen = function(loaded) {
                var obj = this;
                if(!loaded) {
                        obj.css('top', $(window).height()/2-
this.height()/2);
                        obj.css('left', $(window).width()/2-
this.width()/2);
                        $(window).resize(function()
{ obj.centerScreen(!loaded); });
                } else {
                        obj.stop();
                        obj.animate({ top: $(window).height()/2-
this.height()/2, left: $
(window).width()/2-this.width()/2}, 200, 'linear');
                }
        }
});