Sometimes you need to send a dataLayer push on an external/internal URL. This is how you do it properly.

DataLayer eventCallback

$(document).on('click', '.widget-promotion a', function(event) {
  var title = $(this).text().trim();
  var url = $(this).attr('href');
  dataLayer.push({
    'event': 'promotion_click',
    'promotion_title': title,
    'eventCallback': function() { window.location = url },
  });
});