function onScroll()

in site-ui/src/js/01-on-this-page.js [56:85]
27 lines of code
7 McCabe index (conditional complexity)

  function onScroll () {
    // NOTE doc.parentNode.offsetTop ~= doc.parentNode.getBoundingClientRect().top + window.pageYOffset
    //var targetPosition = doc.parentNode.offsetTop
    // NOTE no need to compensate wheen using spacer above [id] elements
    var targetPosition = 0
    var activeFragment
    headings.some(function (heading) {
      if (Math.floor(heading.getBoundingClientRect().top) <= targetPosition) {
        activeFragment = '#' + heading.id
      } else {
        return true
      }
    })
    if (activeFragment) {
      if (activeFragment !== lastActiveFragment) {
        if (lastActiveFragment) {
          links[lastActiveFragment].classList.remove('is-active')
        }
        var activeLink = links[activeFragment]
        activeLink.classList.add('is-active')
        if (menu.scrollHeight > menu.offsetHeight) {
          menu.scrollTop = Math.max(0, activeLink.offsetTop + activeLink.offsetHeight - menu.offsetHeight)
        }
        lastActiveFragment = activeFragment
      }
    } else if (lastActiveFragment) {
      links[lastActiveFragment].classList.remove('is-active')
      lastActiveFragment = undefined
    }
  }