code: function updateSidebar () {
        var top = (doc && doc.scrollTop) || body.scrollTop
        var headerHeight = header.offsetHeight
        if (top > (headerHeight - 25)) {
          // main.classList.add('fix-sidebar')
          header.classList.add('fix-header')
        } else {
          // main.classList.remove('fix-sidebar')
          header.classList.remove('fix-header')
        }
        if (animating || !allLinks) return
        var last
        for (var i = 0; i < allLinks.length; i++) {
          var link = allLinks[i]
          if (link.offsetTop > top) {
            if (!last) last = link
            break
          } else {
            last = link
          }
        }
        if (last) {
          setActive(last.id)
        }
      }
docs: // listen for scroll event to do positioning & highlights window.addEventListener('scroll', updateSidebar) window.addEventListener('resize', updateSidebar)