tion
  let tocLinks = this.$menu.querySelectorAll('#menu-toc li > a');
  for (let i = 0; i < tocLinks.length; i++) {
    let $link = tocLinks[i];
    $link.addEventListener('click', event => {
      this.toggle();
      event.stopPropagation();
    });
  }

  // update active clause on scroll
  window.addEventListener('scroll', debounce(this.updateActiveClause.bind(this)));
  this.updateActiveClause();

  // prevent menu scrolling from scrolling the body
  this.$toc.addEventListener('wheel', e => {
    let 