Extjs Microsoft JScript 运行时错误: 对象不支持“createContextualFragment”属性或方法

<script type="text/javascript">
if ((typeof Range !==
"undefined") && !Range.prototype.createContextualFragment)
{
Range.prototype.createContextualFragment = function (html)
{
var frag =
document.createDocumentFragment(),
div =
document.createElement("div");

frag.appendChild(div);
div.outerHTML =
html;
return frag;
};
}

</script>