cross-domain-linker.js

// Call with decorateUrl('https://www.domain.com/url', 'UA-12345-1');
// Outputs the URL string with the Universal Analytics cross-domain linker in place.
// Tracking ID is optional. If you leave it out, the linker will be built
// with the settings of the first tracker found on the page.
function decorateUrl(urlString, trackingId) {
  var ga = window[window['GoogleAnalyticsObject']];
  if (ga && ga.getAll) {
    var trackers = ga.getAll().filter(function(t) {
      return trackingId ? t.get('trackingId') === trackingId : true;
    });
    var tracker = trackers.length ? trackers[0] : undefined;
    if (tracker) {
      urlString = new window.gaplugins.Linker(tracker).decorate(urlString);
    }
  }
  return urlString;
}