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                        /JavaScript進階篇

這個代碼中的while循環是神馬意思？

<!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 get_nextSibling(n){
??????? var x=n.nextSibling;
??????? while (x && x.nodeType!=1){
??????????? x=x.nextSibling;
??????? }
??????? return x;
??? }
?? ?
??? function get_previousSibling(n){
??????? var x=n.previousSibling;
??????? while (x && x.nodeType!=1){
??????????? x=x.previousSibling;
??????? }
??????? return x;
??? }

??? var x=document.getElementsByTagName("li")[2];
??? document.write(x.nodeName);
??? document.write(" = ");
??? document.write(x.innerHTML);
?? ?
??? var y=get_nextSibling(x);
?? ?
??? if(y!=null){
??????? document.write("<br />nextsibling: ");
??????? document.write(y.nodeName);
??????? document.write(" = ");
??????? document.write(y.innerHTML);
??? }else{
????? document.write("<br>已經是最后一個節點");???? ?
??? }

???? var z=get_previousSibling(x);
???? if(z!=null){
??????? document.write("<br />previoussibling: ");
??????? document.write(z.nodeName);
??????? document.write(" = ");
??????? document.write(z.innerHTML);
??? }else{
????? document.write("<br>這是第一個節點");???? ?
??? }

</script>
</body>
</html>