这么输出节点属性，后面三个结果都是NULL？
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>
<body>
<div>
javascript
<p>javascript</p>
<div>jQuery</div>
<h5>PHP</h5>
</div>
<script type="text/javascript">
var x = document.getElementsByTagName('div')[0].childNodes;
for(var i =0;i<x.length;i++)
{
var a = x[i].nodeValue;
document.write(a+'<br>');
}
</script>
</body>
</html>
