Javascript scrollTop不使用jQuery处理示例？

你能告诉我为什么

scrollTop

不工作吗。事实上，我想滚动焦点，在这里我发出命令来预编文本。 实际上，焦点在文本的前面。我需要焦点移动，保持静止

这是我的小提琴

当我预先结束时，文本焦点转到行的顶部

$("#contend").scroll(function () {
    if ($(this).scrollTop() === 0) {
        alert("ssss");
        $("#pre").prepend(" Distinguished service of a high degree to Australia or to humanity at largefjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf adasda  sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf adasda sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf adasda sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf adasda  sdflkjsdlfjsldfj sdfsjdflsf adasda  sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf adasda sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf adasda sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf sdfjsflsj sdflkjsdlfjsldfj sdfsjdflsf adasda");
        alert($("#pre")[0].scrollHeight)
        $("#pre").prependTo("#contend");
        document.getElementById("content").scrollTop = $("#pre")[0].scrollHeight
    }
});

$("#contend").scroll(function () {
    if ($('#contend').scrollTop() >= $('#contend')[0].scrollHeight - document.body.offsetHeight) {
        $("#pre").html('');
    }
});

我想

$(this).scrollTop() 

永远不会是0

尝试改变

if ($(this).scrollTop() === 0) {

到

if（$（this）.scrollTop（）<1）{

为什么要申请。在同一ID上滚动两次？一次是获取页面顶部，另一次是获取页面底部事件

if( $(this).scrollTop() < 1) {