maichimp javascript get user id

mailchimpmc_cid.js

<script type="text/javascript">
 if(window.location.href.indexOf("&mc_cid")) {
    var a_mc_cid = location.search.split('&')[7];
    var b_mc_cid = a_mc_cid.split('=')[1];
    var a_mc_eid = location.search.split('&')[8];
    var b_mc_eid = a_mc_eid.split('=')[1];
      dataLayer.push ({ 'event': 'mailchimp', 'eventCategory': b_mc_cid, 'eventAction': b_mc_eid, 'eventLabel': '{{WPeventId}}', 'nonInteraction': 1 });
 };
 </script>