scroll滚动到底 按钮可见

    $(document).ready(function() {
        var nScrollHight = 0; //滚动距离总长(注意不是滚动条的长度)
        var nScrollTop = 0; //滚动到的当前位置
        var nDivHight = $("#pdiv").height();
        $("#pdiv").scroll(function() {
            nScrollHight = $(this)[0].scrollHeight;
            nScrollTop = $(this)[0].scrollTop;
            if (nScrollTop + nDivHight >= nScrollHight)
                $("#btsubmit").removeAttr("disabled");
        });
    });