为什么只能改过去，不能改回来
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<div><i id="oldnode">JavaScript</i>是一个很常用的技术，为网页添加动态效果。</div>
<a href="javascript:replaceMessage()"> 将加粗改为斜体</a><br/>
<a href="javascript:replaceMessage1()">将斜体改为粗体</a>
<script type="text/javascript">
function replaceMessage(){
var oldHTML= oldnode.innerHTML;
var newnode=document.createElement("b");
var oldNode=document.getElementById("oldnode");
oldNode.parentNode.replaceChild(newnode,oldNode);
newnode.innerHTML=oldHTML;
}
function replaceMessage1(){
var oldHTML=oldnode.innerHTML;
var newnode=document.createElement("b");
var oldNode=document.getElementById("oldnode");
oldNode.parentNode.replaceChild(newnode,oldNode);
newnode.innerHTML=oldHTML;
}
</script>
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