tooltips.js

;(function() {
 'use strict'

 function removeIds(elem) {
 if (elem instanceof Element) {
 elem.removeAttribute('id')
 for (var i = 0, n = elem.childElementCount; i < n; ++i)
 removeIds(elem.children[i])
 }
 return elem
 }

 function addTips() {
 var tips = []

 function headerOf(elem) {
 if (!elem) return null
 if (/^H[1-6]$/.test(elem.tagName)) return elem
 if (elem.previousElementSibling)
 return headerOf(elem.previousElementSibling)
 return headerOf(elem.parentElement)
 }

 function contextOf(elem) {
 if (!elem) return null
 if (/^H[1-6]$/.test(elem.tagName)) return elem
 if (/^(P|LI)$/.test(elem.tagName)) return elem
 return contextOf(elem.parentElement)
 }

 Array.prototype.slice
 .call(document.querySelectorAll('a'))
 .forEach(function(link) {
 var href = link.getAttribute('href')
 if (!href || href[0] !== '#' || href === '#') return
 if (link.onclick) return

 var target = document.querySelector(href)

 var context = contextOf(target)
 if (!context) return

 if (contextOf(link) === context) return

 if (/^(P|LI)$/.test(context.tagName)) {
 var targetHeader = headerOf(context)
 if (!targetHeader) return

 var targetSibling = document.createElement('p')

 var child = context.firstChild
 while (child) {
 targetSibling.appendChild(removeIds(child.cloneNode(true)))
 child = child.nextSibling
 }

 tips.push({
 link: link,
 targetHeader: removeIds(targetHeader.cloneNode(true)),
 targetSibling: targetSibling
 })
 } else {
 var targetHeader = context

 var targetSibling = targetHeader.nextElementSibling
 if (!targetSibling) return
 if (targetSibling.tagName !== 'P') return

 tips.push({
 link: link,
 targetHeader: removeIds(targetHeader.cloneNode(true)),
 targetSibling: removeIds(targetSibling.cloneNode(true))
 })
 }
 })

 tips.forEach(function(args) {
 var preview = document.createElement('div')
 preview.setAttribute('class', 'preview')
 if (args.targetHeader) preview.appendChild(args.targetHeader)
 preview.appendChild(args.targetSibling)
 args.link.setAttribute('class', 'preview-anchor')
 args.link.appendChild(preview)
 })
 }

 window.addEventListener('load', addTips)
})()