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                        /JavaScript進(jìn)階篇

為什么我的代碼卡死了，把while換成if就又好了

<!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">
var?ul?=?document.getElementsByTagName('ul')[0].firstChild;
var?li?=?get_notext(ul);
document.write(li.nodeName?+?"="?+?li.innerHTML?+?"<br/>");

function?get_notext(li)?{
????while?(li.nodeType?!=?1)?{
????????x?=?li.nextSibling;
????}
????return?x;
}


function?get_nextSibling(li)?{
????var?x?=?li.nextSibling
????while?(x.nodeType?!=?1)?{
????????x?=?x.nextSibling;
????}
????return?x;
}

var?nextLi?=?get_nextSibling(li);
if?(nextLi?!=?null)?{
????document.write(nextLi.nodeName?+?"="?+?nextLi.innerHTML?+?"<br/>");
}?else?{
????document.write("這已經(jīng)是最后一個節(jié)點(diǎn)")
}


function?get_prevSibling(li)?{
????var?x?=?li.previousSibling;
????while?(x.nodeType?!=?1)?{
????????x?=?x.previousSibling;
????}
????return?x;
}

var?u2li?=?document.getElementById("u2").lastChild;
var?prevLi?=?get_prevSibling(u2li);
if?(prevLi?!=?null)?{
????document.write(prevLi.nodeName?+?"="?+?prevLi.innerHTML?+?"<br/>");
}?else?{
????document.write("這已經(jīng)是最后一個節(jié)點(diǎn)")
}

</script>


</body>
</html>