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                        /前端开发
                        
                            /JavaScript
                        
                        /JavaScript进阶篇

无法输出y.nodeName怎么回事

<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>nextSibling</title>
</head>
<body>
<ul id="u1">
            <li id="a">javascript</li>
            <li id="b">jquery</li>
            <li id="c">html</li>
        </ul>
        <ul id="u2">
            <li id="d">css3</li>
            <li id="e">php</li>
            <li id="f">java</li>
        </ul>
<script type="text/javascript">
    function getnext(n){
        var x=n.nextSibling;
        while(x && x.nodeType!=1)
        {
            x=x.nextSibling;
        }
            return x;
    }
    var x=document.getElementsByTagName("li")[0];
        document.write(x.nodeName+"="+x.innerHTML+"<br/");
    var y=getnext(x);
    if(y!=null){
        document.write(y.nodeName+"="+y.innerHTML);
       }
     else{
        document.write("已经是最后一个节点")
     }
</script>
</body>
</html>