document.getElementByTagName("div")[0]和oldnode.parentnode不是一样的吗？为什么不能运行
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>无标题文档</title>
</head>
<body>
<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 newnode= document.createElement("i");
var nodetext=document.createTextNode("JavaScript");
newnode.appendChild(nodetext);
var oldnode=document.getElementById("oldnode");
document.getElementByTagName("div")[0].replaceChild(newnode,oldnode);
}
</script>
</body>
</html>
