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                        /JavaScript進(jìn)階篇

請問代碼中的(x && x.nodeType!=1)是什么意思？

<!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;
??? }
??? var x=document.getElementsByTagName("li")[4];
??? 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(jīng)是最后一個節(jié)點");?????
??? }
???
??? function get_previousSibling(n)
??? {
??????? var x=n.previousSibling;
??????? while (x && x.nodeType!=1)
??????? {
??????????? x=x.previousSibling;
??????? }
??????? return x;
??? }
???
??? var z=get_previousSibling(x);???
??? if(z!=null)
??? {
??????? document.write("<br />nextpreviousSibling:");
??????? document.write(z.nodeName);
??????? document.write("=");
??????? document.write(z.innerHTML);
??? }
??? else{
??????? document.write("<br>已經(jīng)是第一個節(jié)點了")
??? }
</script>
</body>
</html>