偶写的代码：
<!DOCTYPE html>
<html lang="zh-cn">
<head>
<meta charset="UTF-8">
<link rel="stylesheet" href="base.css" />
<script type="text/javascript" src="jquery-1.10.1.min.js" ></script>
</head>
<body>
<style>
#goTop{ width: 40px; height: 40px; background: #f60; text-align: center; line-height: 20px;
color: #fff; position: fixed; bottom: 20px; right: 20px;}
</style>
<div style="height: 3000px;"></div>
<div id="goTop">回到顶部</div>
<script>
$(function(){
goTop();
});
function goTop(){
$('#goTop').click(function(){$('html,body').animate({scrollTop: '0'}, 800);});
}
</script>
</body>
</html>
效果图：
结果群友（贾顺名）直接写出使用#号的解决方法：
<!DOCTYPE html>
<html lang="zh-cn">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
<link rel="stylesheet" href="base.css" />
</head>
<body>
<style>
.goTop{ width: 40px; height: 40px; background: #f60; text-align: center; line-height: 20px;
color: #fff; position: fixed; bottom: 20px; right: 20px;}
</style>
<script>document.write('<p>some text</p>'.repeat(200));</script>
<a href="#top" class="goTop">回到顶部</a>
</body>
</html>
效果图：