$(window).scroll(function () {
        var scrollTop = $(this).scrollTop();
        var scrollHeight = $(document).height();
        var windowHeight = $(this).height();
        if (scrollTop + windowHeight == scrollHeight) {
        // append after之类的操作
        }
    });

判断滚动条到底部，需要用到DOM的三个属性值
即scrollTop, clientHeight, scrollHeight

scrollTop为滚动条在Y轴上的滚动距离
clientHeight为内容可视区域的高度
scrollHeight为内容可视区域的高度加上溢出（滚动）的距离

滚动条到底部的条件为
scrollTop + clientHeight == scrollHeight
--
修改:sanfei FROM 113.88.179.*
FROM 113.88.179.*