Cross domain tracking: Migrate Universal Analytics linkerParam to Analytics 4

Question

In Universal Analytics when we used cross domain tracking, we were able to add our custom param to any url with the following code. It appends the _ga= param to the urls.

function getUrl(url) {

    var linkerParam;


    if (typeof ga === 'function' && ga) {
        ga(function () {
            var trackers = ga.getAll();
            linkerParam = trackers[0].get('linkerParam');
        });
    }
    
    return (linkerParam ? url + '?' + linkerParam : url);
}

Analytics 4 introduced a new system, where you list your domains to the property and Analytics 4 handle the cross domain tracking automatically. In rare cases this does not work, for example when you need to generate your own urls via Javascript. There is currently no official solution for that.

Answer 1

I checked how Analytics 4 handles cross domain tracking and come up with the following code based on the original implementation. This code will append the new _gl param to the given url.

You will need to provide your measurement ID without the starting G- to the getLinkerParam function.

function getUrl(url) {

    var linkerParam;

    try {
        linkerParam = getLinkerParam('*** MEASUREMENT ID without G- ***');
    } catch (e) {
    }

    return (linkerParam ? url + '?' + linkerParam : url);
}


function getLinkerParam(measurement_id) {

    var data = {};

    var parts1 = document.cookie.match('(^|;)\\s*_ga\\s*=\\s*([^;]+)').pop().split('.');
    parts1.shift();
    parts1.shift();
    data._ga = parts1.join('.');

    var parts2 = document.cookie.match('(^|;)\\s*_ga_' + measurement_id + '\\s*=\\s*([^;]+)').pop().split('.');
    parts2.shift();
    parts2.shift();
    data['_ga_' + measurement_id] = parts2.join('.');


    function kf() {
        for (var a = lf, b = {}, c = 0; c < a.length; ++c)
            b[a[c]] = c;
        return b
    }

    function mf() {
        var a = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        a += a.toLowerCase() + "0123456789-_";
        return a + "."
    }

    var lf,
        nf, qf;

    function of(a) {
        lf = lf || mf();
        nf = nf || kf();
        for (var b = [], c = 0; c < a.length; c += 3) {
            var d = c + 1 < a.length,
                e = c + 2 < a.length,
                f = a.charCodeAt(c),
                h = d ? a.charCodeAt(c + 1) : 0,
                k = e ? a.charCodeAt(c + 2) : 0,
                l = f >> 2,
                n = (f & 3) << 4 | h >> 4,
                q = (h & 15) << 2 | k >> 6,
                r = k & 63;
            e || (r = 64, d || (q = 64));
            b.push(lf[l], lf[n], lf[q], lf[r])
        }
        return b.join("")
    }

    var Df = function (a) {
            var b = [],
                c;
            for (c in a)
                if (a.hasOwnProperty(c)) {
                    var d = a[c];
                    void 0 !== d && d === d && null !== d && "[object Object]" !== d.toString() && (b.push(c), b.push(of(String(d))))
                }
            var e = b.join("*");
            return ["1", Cf(e), e].join("*")
        },
        Cf = function (a, b) {
            var c = [window.navigator.userAgent, (new Date).getTimezoneOffset(), window.navigator.userLanguage || window.navigator.language, Math.floor((new Date).getTime() / 60 / 1E3) - (void 0 === b ? 0 : b), a].join("*"),
                d;
            if (!(d = qf)) {
                for (var e = Array(256), f = 0; 256 > f; f++) {
                    for (var h = f, k = 0; 8 > k; k++)
                        h = h & 1 ? h >>> 1 ^ 3988292384 : h >>> 1;
                    e[f] = h
                }
                d = e
            }
            qf = d;
            for (var l = 4294967295, n = 0; n < c.length; n++)
                l = l >>> 8 ^ qf[(l ^ c.charCodeAt(n)) & 255];
            return ((l ^ -1) >>> 0).toString(36)
        };

    return "_gl=" + Df(data);
}