function onScroll()

in antora-ui/src/js/02-on-this-page.js [50:95]
46 lines of code
17 McCabe index (conditional complexity)

  function onScroll () {
    var scrolledBy = window.pageYOffset
    var buffer = getNumericStyleVal(document.documentElement, 'fontSize') * 1.15
    var ceil = article.offsetTop
    if (scrolledBy && window.innerHeight + scrolledBy + 2 >= document.documentElement.scrollHeight) {
      lastActiveFragment = Array.isArray(lastActiveFragment) ? lastActiveFragment : Array(lastActiveFragment || 0)
      var activeFragments = []
      var lastIdx = headings.length - 1
      headings.forEach(function (heading, idx) {
        var fragment = '#' + heading.id
        if (idx === lastIdx || heading.getBoundingClientRect().top + getNumericStyleVal(heading, 'paddingTop') > ceil) {
          activeFragments.push(fragment)
          if (lastActiveFragment.indexOf(fragment) < 0) links[fragment].classList.add('is-active')
        } else if (~lastActiveFragment.indexOf(fragment)) {
          links[lastActiveFragment.shift()].classList.remove('is-active')
        }
      })
      list.scrollTop = list.scrollHeight - list.offsetHeight
      lastActiveFragment = activeFragments.length > 1 ? activeFragments : activeFragments[0]
      return
    }
    if (Array.isArray(lastActiveFragment)) {
      lastActiveFragment.forEach(function (fragment) {
        links[fragment].classList.remove('is-active')
      })
      lastActiveFragment = undefined
    }
    var activeFragment
    headings.some(function (heading) {
      if (heading.getBoundingClientRect().top + getNumericStyleVal(heading, 'paddingTop') - buffer > ceil) return true
      activeFragment = '#' + heading.id
    })
    if (activeFragment) {
      if (activeFragment === lastActiveFragment) return
      if (lastActiveFragment) links[lastActiveFragment].classList.remove('is-active')
      var activeLink = links[activeFragment]
      activeLink.classList.add('is-active')
      if (list.scrollHeight > list.offsetHeight) {
        list.scrollTop = Math.max(0, activeLink.offsetTop + activeLink.offsetHeight - list.offsetHeight)
      }
      lastActiveFragment = activeFragment
    } else if (lastActiveFragment) {
      links[lastActiveFragment].classList.remove('is-active')
      lastActiveFragment = undefined
    }
  }