这样为什么不行,哪错了
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>
<body>
<ul id="test">
<li>JavaScript</li>
<li>HTML</li>
</ul>
<script type="text/javascript">
var otest = document.getElementById("test");
var x=otest.lastChild;
var a=document.createElement("li")
a.innerHTML="php";
otest.insertBefore(a,x)
</script>
</body>
</html>