(function($) {  
        jQuery.fn.center = function () {  
            this.css('position','absolute');  
             this.css('top', ( $(window).height() - this.height() ) / +$(window).scrollTop() + 'px');  
             this.css('left', ( $(window).width() - this.width() ) / 2+$(window).scrollLeft() + 'px');  
             return this;  
        }  
    })(jQuery);  //调用：$("#macoArea").center();

//javascript/1070