add lazy loading to WP, more info at http://plugins.jquery.com/project/lazyload

jQuery Image Lazy Load WP

SOGO

Tested with Gutenberg
Create a simple way to add javascript code to individual page post or custom post type header and footer, 
for example: add conversion code to thank you pages 
add google re-marketing code to individual pages 
and much more… 
added in version 1.3 the option to add script \ style to all pages not only individual pages, 
 this will allow you to add Google re-marketing code to the entire site or Google Analytics 
 to use it goto “settings” – “Header Footer Settings”
New Features (version 3.0): 
Added option for terms / category pages
New Features (version 2.3): 
 Added support for WooCommerce shop page.
<ol>
<li>
we support now exclude individual pages form printing the header and footer scripts, this is supported by 2 checkboxes in each page\post 
buy check it the script will not be display on this page
</li>
<li>
we added support to limit the script only for certain post type \ page
</li>
</ol>
if you like it \ use it – please rate us.
usage: 
You need to paste the code with the script tag, for example: 
 you js code

SOGO Add Script to Individual Pages Header Footer

Simple plugin to add script to header and footer for individual pages & posts

jQuery Image Lazy Load WP vs SOGO Add Script to Individual Pages Header Footer