XML parsing of a variable string in JavaScript

Updated answer for 2017

The following will parse an XML string into an XML document in all major browsers. Unless you need support for IE <= 8 or some obscure browser, you could use the following function:

function parseXml(xmlStr) {
   return new window.DOMParser().parseFromString(xmlStr, "text/xml");
}

If you need to support IE <= 8, the following will do the job:

var parseXml;

if (typeof window.DOMParser != "undefined") {
    parseXml = function(xmlStr) {
        return new window.DOMParser().parseFromString(xmlStr, "text/xml");
    };
} else if (typeof window.ActiveXObject != "undefined" &&
       new window.ActiveXObject("Microsoft.XMLDOM")) {
    parseXml = function(xmlStr) {
        var xmlDoc = new window.ActiveXObject("Microsoft.XMLDOM");
        xmlDoc.async = "false";
        xmlDoc.loadXML(xmlStr);
        return xmlDoc;
    };
} else {
    throw new Error("No XML parser found");
}

Once you have a Document obtained via parseXml, you can use the usual DOM traversal methods/properties such as childNodes and getElementsByTagName() to get the nodes you want.

Example usage:

var xml = parseXml("<foo>Stuff</foo>");
alert(xml.documentElement.nodeName);

If you’re using jQuery, from version 1.5 you can use its built-in parseXML() method, which is functionally identical to the function above.

var xml = $.parseXML("<foo>Stuff</foo>");
alert(xml.documentElement.nodeName);