<script>
  (function($) {
    $(document).ajaxSuccess(function( event, xhr, settings ) {

      var responseText = JSON.parse(xhr.responseText);
      var leadSource = responseText.leadSource;

      dataLayer.push({
        'event': 'ajaxSuccess',
        'eventCategory': 'AJAX',
        'eventAction': settings.url,
        'eventLabel': leadSource
      });
    });
  })
  (jQuery);
</script>