为什么我这样改变不了斜体，求解
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<title>无标题文档</title>
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<div><b id="oldnode">JavaScript</b>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>
<script type="text/javascript">
function replaceMessage(){
var oldNode = document.getElementById("oldnode");
var newnode = document.createElement("i");
var newnodeText = doucument.createTextNode(oldNode.innerHTML);
newnode.appendChild(newnodeText);
oldNode.parentNode.replaceChild(newnode,oldNode);
}
</script>
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</html>
