这个为什么无效
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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(){
document.write (document.getElementsByTagName("b"));
var soub=document.getElementsByTagName("b");
var soubh=soub.innerHTML;
var newb=document.creatElement("i");
soub.parentNode.replaceChild(newb,soub);
newb.innerHTML=soubh;
}
</script>
</body>
</html>
