求助求助？怎么实现换行插入
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>
<body>
<script type="text/javascript">
var main = document.body;
//创建链接
function createa(url,text)
{var a=document.createElement("a");
a.href=url;
a.innerHTML=text;
a.style.color="red";
main.appendChild(a);
}
// 调用函数创建链接
createa("http://www.imooc.com/","慕课网");
var br=document.createElement("br");
var body=document.getElementsByTagName("body");
body.insertBefore(br,body.childNodes[0]);
createa("http://www.xiaokanba.com","小看吧");
</script>
</body>
</html>
