Polymer('my-elemen', {
  ready: function () {
    this.swiperContainer = this.shadowRoot.querySelector('swiper-container');
  },
  domReady: function () {
    $(this.swiperContainer).swiper({
      mode:'horizontal',
      loop: true
    });
  }
}

var counter = document.querySelector('#counter');
  counter.count = 0;
  counter.addEventListener('click', function (event) {
    if (event.target.tagName == 'button-element') {
      counter.count++;
      counter.textContent = counter.count; 
    }
  });