document.body.scrollTop 要改成 document.documentElement.scrollTop不然不生效
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div onclick="GoTop();" style=" 50px;height: 50px;background-color: black;color: white;
position: fixed;
bottom:20px;
right: 20px;
">返回顶部</div>
<div style="height: 5000px;background-color: #dddddd;">
正文
</div>
<script>
function GoTop(){
document.body.scrollTop = 0;
}
</script>
</body>
</html>