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.

bypr.nils

Smart Image Loader loads images which are visible in the initial viewport of your website before any images whose position is “below the fold”, outside the current viewport. Those images can be loaded as soon as the visible images are finished loading or “lazy loaded” when they would become visible. This can be useful for bandwidth saving on mobile devices.
There is no need to insert any additional code into your website, just install the plug-in.
The default settings are fine in most cases, but you may want to adjust them for optimization.
Smart Image Loader is tested and works down to Internet Explorer 7, disabled below.
Note: there is currently no support for (CSS) background images.

Smart Image Loader

Smart Image Loader is a fire-and-forget priority and lazy loader for image sources. Can be a huge performance boost especially for one pagers.

jQuery & Plugins Asynchronous Loader vs Smart Image Loader