bindFocusEvents() {
    if (!this.isInput) return;
    this.el.addEventListener('focus', (e) => {
      this.stop();
    });
    this.el.addEventListener('blur', (e) => {
      if (this.el.value && this.el.value.length !== 0) {
        return;
      }
      this.start();
    });
  }
If using input elements, bind focus in order to
start and stop the animation
@private