AnchorJS Example https://github.com/bryanbraun/anchorjs

AnchorJS.js

<script>
  
/**
 * Example 1
 */
anchors.options = {
  placement: 'right',
  visible: 'hover',
};



// Add anchors on DOMContentLoaded (Optionable... where you load it, you don't have to, that's as far back as it can go or so)
document.addEventListener("DOMContentLoaded", function(event) {
    anchors.add('article h1, article h2, article h3') .remove('.no-anchor');
    
  });
  
</script>

HTML5 Stuff

use article is best.
in posts.html works great in Jekyll.

<article>
{{ content }}
</article>

https://www.w3schools.com/html/html5_semantic_elements.asp
https://code.tutsplus.com/tutorials/html-5-and-css-3-the-techniques-youll-soon-be-using--net-5708

Pre defined... (Semantic HTML5) (Sections... instead of headers)

<section id="section-1">
  <h3 data-anchor-id="section-1">Section 1</h3>
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed...</p>
</section>

<!-- ... -->

<script>
  anchors.add('h3');
</script>

or

generate a table of contents

with it (anchorJS)...
https://jsfiddle.net/bryanbraun/nc6rL9hk/

links

from: https://github.com/bryanbraun/anchorjs