last (lastClassName) {

    if (typeof lastClassName !== 'undefined')
      this.addClass(lastClassName);

    this.last_.layout = this.element_.getBoundingClientRect();
    this.last_.opacity =
        parseFloat(window.getComputedStyle(this.element_).opacity);
  }
Applies the class that moves the element to its last position. It then
takes a snapshot of the element's final location and opacity.

@param {string} [lastClassName] - The class name applied to the element
 that moves it to its final position.