XML to JavaScript Object

The following function parses XML and returns a JavaScript object with a scheme that corresponds to the XML. XML siblings w/ the same name are collapsed into arrays. nodes with names that can be found in the arrayTags parameter (array of tag name strings) always yield arrays even in case of only one tag occurrence. arrayTags can be omitted. Text nodes with only spaces are discarded.

function parseXml(xml, arrayTags) {
    let dom = null;
    if (window.DOMParser) dom = (new DOMParser()).parseFromString(xml, "text/xml");
    else if (window.ActiveXObject) {
        dom = new ActiveXObject('Microsoft.XMLDOM');
        dom.async = false;
        if (!dom.loadXML(xml)) throw dom.parseError.reason + " " + dom.parseError.srcText;
    }
    else throw new Error("cannot parse xml string!");

    function parseNode(xmlNode, result) {
        if (xmlNode.nodeName == "#text") {
            let v = xmlNode.nodeValue;
            if (v.trim()) result['#text'] = v;
            return;
        }

        let jsonNode = {},
            existing = result[xmlNode.nodeName];
        if (existing) {
            if (!Array.isArray(existing)) result[xmlNode.nodeName] = [existing, jsonNode];
            else result[xmlNode.nodeName].push(jsonNode);
        }
        else {
            if (arrayTags && arrayTags.indexOf(xmlNode.nodeName) != -1) result[xmlNode.nodeName] = [jsonNode];
            else result[xmlNode.nodeName] = jsonNode;
        }

        if (xmlNode.attributes) for (let attribute of xmlNode.attributes) jsonNode[attribute.nodeName] = attribute.nodeValue;

        for (let node of xmlNode.childNodes) parseNode(node, jsonNode);
    }

    let result = {};
    for (let node of dom.childNodes) parseNode(node, result);

    return result;
}