code: function play() {
      var _this2 = this;
  
      var fullscreen = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : false;
  
      if (!this.isShown || this.played) {
        return this;
      }
  
      var options = this.options,
          player = this.player;
  
      var onLoad = this.loadImage.bind(this);
      var list = [];
      var total = 0;
      var index = 0;
  
      this.played = true;
      this.onLoadWhenPlay = onLoad;
  
      if (fullscreen) {
        this.requestFullscreen();
      }
  
      addClass(player, CLASS_SHOW);
      forEach(this.items, function (item, i) {
        var img = item.querySelector('img');
        var image = document.createElement('img');
  
        image.src = getData(img, 'originalUrl');
        image.alt = img.getAttribute('alt');
        total += 1;
        addClass(image, CLASS_FADE);
        toggleClass(image, CLASS_TRANSITION, options.transition);
  
        if (hasClass(item, CLASS_ACTIVE)) {
          addClass(image, CLASS_IN);
          index = i;
        }
  
        list.push(image);
        addListener(image, EVENT_LOAD, onLoad, {
          once: true
        });
        player.appendChild(image);
      });
  
      if (isNumber(options.interval) && options.interval > 0) {
        var play = function play() {
          _this2.playing = setTimeout(function () {
            removeClass(list[index], CLASS_IN);
            index += 1;
            index = index < total ? index : 0;
            addClass(list[index], CLASS_IN);
            play();
          }, options.interval);
        };
  
        if (total > 1) {
          play();
        }
      }
  
      return this;
    }
docs: Play the images
  @param {boolean} [fullscreen=false] - Indicate if request fullscreen or not.
  @returns {Viewer} this