TOC.js

// prepare the array by adding level, ID and parent to each item of the array
function prepare (array) {
  let level, t
  for (let i = 0, n = array.length; i < n; i++) {
    t = array[i]
    t.el = t
    level = parseInt(t.tagName[1], 10)
    t.level = level
    t.idt = i + 1

    if (level <= 1) t.parent = 0
    if (i) {
      if (array[i - 1].level < level) {
        t.parent = array[i - 1].idt
      } else if (array[i - 1].level === level) {
        t.parent = array[i - 1].parent
      } else {
        for (let j = i - 1; j >= 0; j--) {
          if (array[j].level === level - 1) {
            t.parent = array[j].idt
            break
          }
        }
      }
    }
  }
  return array
}

// transform a flat array in a hierarchical array
function hierarchical (items) {
  const hashTable = Object.create(null)
  items.forEach(item => hashTable[item.idt] = { ...item, subitems: [] })
  const tree = []
  items.forEach(item => {
    if (item.parent) {
      hashTable[item.parent].subitems.push(hashTable[item.idt])
    } else {
      tree.push(hashTable[item.idt])
    }
  })
  return tree
}

// return an UL containing each title in a LI and possibly other items in UL sub-lists.
function addList (titles) {
  let li, a, anchor
  // let base = document.querySelector('head base')['href']+'admin-update/';
  const base = document.location.href.split('#')[0]
  const ol = document.createElement('ol')
  if (titles && titles.length) {
    let t
    for (t of titles) {
      if (t.el.id) anchor = t.el.id
      else anchor = t.el.textContent
      if (!anchor) anchor = 'inconnu'
      anchor = anchor.replace(/\W/g, '')
      t.el.id = anchor
      li = document.createElement('li')
      a = document.createElement('a')
      a.href = base + `#${anchor}`
      a.innerHTML = t.el.textContent
      li.append(a)
      if (t.subitems && t.subitems.length) {
        li.append(addList(t.subitems))
      }
      ol.append(li)
    }
  }
  return ol
}

// get the toc element
const divtoc = document.getElementById('toc')

// get the article element
const article = document.getElementById('content')

if (divtoc && article) {
  let titles = article.querySelectorAll('h1, h2, h3')
  titles = prepare(titles)
  titles = hierarchical(titles)
  const olRacine = addList(titles)
  divtoc.append(olRacine)
}