mabujo

Featured Image Sharpen Up makes a tiny version of your featured post image and places it in the head of the page. 
As you scroll down the page, some JavaScript lazy loads the featured images in the background and replaces the tiny images as the full images are loaded.
You may have seen a similar effect used for images on medium.com.
Created on WordPress 4.4, but should work on earlier versions. 
Tested working on all Twenty Sixteen, Twenty Fifteen, Twenty Fourteen, Twenty Thirteen, Twenty Twelve and Twenty Eleven themes. Should work on other themes, but may need CSS adjustments, depending on theme handling of featured images.
Uses jQuery.Lazy(); (http://jquery.eisbehr.de/lazy/) and Hugh Lashbrooke’s plugin template (https://github.com/hlashbrooke/WordPress-Plugin-Template)
Plugin page : <a href="https://mabujo.com/blog/featured-image-sharpen-up-wordpress-plugin/" rel="nofollow ugc">Featured Image Sharpen Up plugin @ mabujo</a>

Featured Image Sharpen Up

This plugin helps increase the page loading speed of your site by replacing featured post images with a small inline image, and lazy loading the full  …

Duck Dev

Joel James

Comments are heavy. A long thread can pull in dozens of avatars, gravatar lookups and reply scripts — all of which the browser downloads before the visitor has even reached them. Lazy Load for Comments defers all of that until the visitor either scrolls to the comments area or clicks a button.
The result: fewer HTTP requests, faster Largest Contentful Paint and a happier Lighthouse score, without changing how your comment template looks.
Version 2.0 is a complete rewrite. It uses the WordPress REST API to fetch the rendered comments on demand and works with both classic themes (<code>comments_template()</code>) and block themes (the core Comments block) out of the box.
<blockquote>
<h4>Features</h4>
<ul>
<li>Lazy-load comments on scroll, on button click, or turn the plugin off without deactivating it.</li>
<li>Works with classic themes and block themes (the core Comments block).</li>
<li>Loads comments inline for search engine crawlers, so indexing and SEO are not affected.</li>
<li>Per-post cache of the rendered Comments block — REST renders stay fast.</li>
<li>Minimum-comment-count threshold so short threads still render inline.</li>
<li>Customisable load-button text, style and extra CSS classes.</li>
<li>Clean React settings page under Comments → Lazy Load.</li>
<li>No jQuery dependency. Front-end script is vanilla JS and intentionally small.</li>
<li>Translation-ready. Hooks and filters available for further customisation.</li>
</ul>
</blockquote>
Useful links
<ul>
<li><a href="https://duckdev.com/product/lazy-load-for-comments/" rel="nofollow ugc">Plugin website</a></li>
<li><a href="https://docs.duckdev.com/lazy-load-for-comments/" rel="nofollow ugc">Documentation</a></li>
<li><a href="https://wordpress.org/support/plugin/lazy-load-for-comments/" rel="ugc">Support forum</a></li>
</ul>

Lazy Load for Comments

Speed up your posts by lazy-loading the WordPress comments on scroll or click. Works with classic and block themes.

Featured Image Sharpen Up vs Lazy Load for Comments