custom-metric-head-link.js

var nodes = document.querySelectorAll("head link");
var linkNodes = [];

if (nodes) {
    for (var i = 0, len = nodes.length; i < len; i++) {
        var node = nodes[i];
        var attributes = Object.values(node.attributes);
        var el = {};

        for (var n = 0, len2 = attributes.length; n < len2; n++) {
            var attribute = attributes[n];
            el[attribute.name.toLowerCase()] = attribute.value;
        }

        linkNodes.push(el);
    }
}
console.log(linkNodes);
return JSON.stringify(linkNodes);