Grab GA4 "linkerParam"

getGa4LinkerParam.js

var getGa4LinkerParam = function() {
    try {
        if (!window.google_tag_data || !window.google_tag_data.glBridge)
            return;
        var cookies = {};
        ('; ' + document.cookie).split('; ').forEach(function(ck) {
            var name = ck.split("=")[0];
            var value = ck.split("=")[1];
            if (name && value && name.match(/^_ga$|^_ga_[A-Z,0-9]/)) {
                cookies[name] = value.match(/[A-Z,0-9]\.[0-9]\.(.*)/)[1];
            }
            if (name && value && name === "FPLC") {
                cookies["_fplc"] = value;
            }
        });
        return "_gl=" + google_tag_data.glBridge.generate(cookies)
    } catch (e) {}
}