https://torch.ch/static/linkify.js

1[].slice.apply(
2  document.querySelectorAll(
3    'article h2, article h3, article h4'
4  )
5).forEach(function(header) {
6  var slug = header.innerText
7    .toLowerCase()
8    .replace(/[^a-z0-9]/g, '-')
9    .replace(/-+/g, '-')
10    .replace(/^-|-$/g, '');
11
12  var hashref = document.createElement('a');
13  hashref.id = slug;
14  hashref.className = 'hashref';
15  header.appendChild(hashref);
16
17  var hash = document.createElement('a');
18  hash.className = 'hash';
19  hash.href = '#' + slug;
20  hash.innerText = '#';
21  header.appendChild(hash);
22});