jquery实现弹出div,始终显示在屏幕正中间的简单实例

 //让指定的DIV始终显示在屏幕正中间   
    function setDivCenter(divName){   
        var top = ($(window).height() - $(divName).height())/2;   
        var left = ($(window).width() - $(divName).width())/2;   
        var scrollTop = $(document).scrollTop();   
        var scrollLeft = $(document).scrollLeft();   
        $(divName).css( { position : 'absolute', 'top' : top + scrollTop, left : left + scrollLeft } ).show();  
    }