main1.appendChild(createa("http://www.imooc.com","慕课网")
<body>
<script type="text/javascript">
var main1 = document.body;
//创建链接
function createa(url,text)
{
var alink = document.createElement("a");
alink.setAttribute("href",url);
alink.innerHTML=text;
return alink;
}
// 调用函数创建链接
main1.appendChild(createa("http://www.imooc.com","慕课网"));
</script>
</body>
加粗部分怎么解释？createa是哪里来的？
