web/_includes/toc.html

{% assign enable_toc = false %}
{% if site.toc and page.toc %}
  {% if page.content contains '<h2' or page.content contains '<h3' %}
    {% assign enable_toc = true %}
  {% endif %}
{% endif %}

{% if enable_toc %}
  <div id="toc-wrapper" class="pl-0 pr-4 mb-5">
    <div class="panel-heading pl-3 pt-2 mb-2">{{- site.data.locales[include.lang].panel.toc -}}</div>
    <nav id="toc"></nav>
  </div>

  <!-- toc.js will be loaded at medium priority -->
  <script src="{{ site.data.assets[origin].toc.js | relative_url }}"></script>
{% endif %}