GA - clientId

function() {
  var dataLayer = window.dataLayer;
  var customDimensionIndex = 1;
  return function(model) {
    model.set('dimension' + customDimensionIndex, model.get('clientId'));
    var cid = model.get('clientId');
    dataLayer.push({'event':'trackerReady',
        'cid':cid});
  }
}