listen () {
    if (this.ready()) {

      window.addEventListener("resize", () => {

        setTimeout(() => {
          this.positionItems();
        }, REPOSITIONING_DELAY);

      });

      this.observeContainerResize();
      this.positionItems();
      this.emit(READY_EVENT);
    }
    else this.getReady();
  }
Positions all the items and
repositions them whenever the
window size changes.