Vitalii Rizo

Loading of JavaScript resources should be done asynchronously, in a non-blocking manner, so the load time of your webpage will not be affected (it would not be delayed by render-blocking JavaScript). But using of deferring or async loading of jQuery causes lots of problems with jQuery plugins. This plugin replaces default WordPress’s JS loader with a special jQuery loader (jQl), that’s why there are no any errors with jQuery plugins.
It’s highly recommended to use any concatenate plugin, e.g., Fast Velocity Minify or WP Fastest Cache. Please, do not add jQuery to the ignore list, because this plugin fixes “undefined jQuery” errors on the console log. Also, it is allowed to use defer or async parsing of JS files.
It requires WordPress 4.1 and newer.
It is available in English and Russian.

jQuery & Plugins Asynchronous Loader

This plugin asynchronously loads jQuery and its plugins without "jQuery is undefined" errors.

Frank Goossens

Deny Dias

This plugin extends Autoptimize to automatically create critical CSS rules. These rules inject the correct critical CSS in different types of pages to ensure these pages are rendered even before the full CSS is loaded, improving the “start to render time” and user experience. For this purpose the plugin integrates with criticalcss.com, a 3rd party service, to have it generate the critical CSS (see <a href="https://wordpress.org/plugins/autoptimize-criticalcss/#faq">FAQ for info on pricing</a>).
Simply install and activate the plugin (you will need to have Autoptimize up and running), enter your <a href="https://criticalcss.com/?aff=1" rel="nofollow ugc">https://criticalcss.com</a> API key and the plugin will automatically start work to create rules.
If you want to change settings or review the rules, you can find these by clicking the “critical css” tab on the Autoptimize plugin settings screen. There are “installation instructions” and more info in <a href="https://wordpress.org/plugins/autoptimize-criticalcss/#faq">the FAQ</a>.

Autoptimize criticalcss.com power-up

Its configuration definitely has a learning curve, but when you get the hang of it, this plugin becomes essential to your website!

Close to perfect

Autoptimize criticalcss.com power-up adds automated critical css creation to Autoptimize integrating with the https://criticalcss.com service.

jQuery & Plugins Asynchronous Loader vs Autoptimize criticalcss.com power-up