iframe_cross_domain_tracking_parent

<script>
/*
*  adapted from https://developers.google.com/analytics/devguides/collection/analyticsjs/cross-domain#iframes
*  I wrapped the whole thing in a setTimeout, so I could observe the delayed execution time
*  of the GA function in the JavaScript console, using the GA debugger Chrome plugin.
*  alternatively, you could just wrap the frameWindow.postMessage in a setTimeout
*/

setTimeout(function(){ 
  ga(function(tracker) {
    var clientId = tracker.get('clientId');
    var frameWindow = document.getElementById('destination-frame').contentWindow;
    // change https://xyz.shoppingcart.com to match your iFrame domain
    frameWindow.postMessage(clientId, 'https://xyz.shoppingcart.com'); 
  });
}, 2000); 
// I decided on a 2 second timeout by trial and error. In my case, this seemed to be
// long enough to allow the iFrame to load > 95% of the time. Increasing the delay too
// much risks having the user move on before being tracked at all

</script>