Multi-Domain Cookie & First-Party Context Preserver Script

Writes first-party cookies to the root domain and syncs values with localStorage to prevent tracking resets.

(function() {
  function getRootDomain() {
    var parts = window.location.hostname.split('.');
    if (parts.length <= 2) return window.location.hostname;
    return '.' + parts.slice(-2).join('.');
  }

  function setRootCookie(name, value, days) {
    var expires = '';
    if (days) {
      var d = new Date();
      d.setTime(d.getTime() + (days * 24 * 60 * 60 * 1000));
      expires = '; expires=' + d.toUTCString();
    }
    var domain = getRootDomain();
    document.cookie = name + '=' + encodeURIComponent(value) + expires + '; path=/; domain=' + domain + '; SameSite=Lax; Secure';
  }

  function syncContext(key) {
    var match = document.cookie.match(new RegExp('(^| )' + key + '=([^;]+)'));
    var cookieVal = match ? decodeURIComponent(match[2]) : null;
    var storageVal = null;
    try { storageVal = localStorage.getItem('gg_' + key); } catch(e) {}

    if (cookieVal && !storageVal) {
      try { localStorage.setItem('gg_' + key, cookieVal); } catch(e) {}
    } else if (!cookieVal && storageVal) {
      setRootCookie(key, storageVal, 90);
    }
  }

  // Preserve critical advertising and analytics identifiers
  ['_fbp', '_fbc', '_ga', 'user_id'].forEach(syncContext);
})();