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>