如何跨浏览器读取xml文档

function createDocument() {
var xmlDoc;
if (window.ActiveXObject) {
var versions =
[
"Msxml2.DOMDocument.6.0",
"Msxml2.DOMDocument.3.0"
];
for (var i = 0; i < versions.length; i++) {
try {
xmlDoc = new ActiveXObject(versions[i]);
return xmlDoc;
} catch (error) {
//do nothing here.
}
}
}
else if (document.implementation && document.implementation.createDocument) {
xmlDoc = document.implementation.createDocument("","",null);
return xmlDoc;
}
return null;
}