fly_out_nav.js

export const calculateTop = (boundingRect, outerHeight) => {
  const windowHeight = window.innerHeight;
  const bottomOverflow = windowHeight - (boundingRect.top + outerHeight);

  return bottomOverflow < 0 ? boundingRect.top - Math.abs(bottomOverflow) : boundingRect.top;
};

export const createArrowStyles = (boundingRect, top) => `.sidebar-sub-level-items::before { transform: translate3d(0, ${boundingRect.top - top}px, 0); }`;

export default () => {
  const style = document.createElement('style');
  document.head.appendChild(style);

  $('.sidebar-top-level-items > li:not(.active)').on('mouseover', (e) => {
    const $this = e.currentTarget;
    const $subitems = $('.sidebar-sub-level-items', $this).show();

    if ($subitems.length) {
      const boundingRect = $this.getBoundingClientRect();
      const top = calculateTop(boundingRect, $subitems.outerHeight());

      $subitems.css({
        transform: `translate3d(0, ${top}px, 0)`,
      });

      style.sheet.insertRule(createArrowStyles(boundingRect, top), 0);
    }
  }).on('mouseout', (e) => {
    $('.sidebar-sub-level-items', e.currentTarget).hide();

    if (style.sheet.rules.length) {
      style.sheet.deleteRule(0);
    }
  });
};