Async JavaScript的作者是Frank Goossens (futtta),目前有100,000+个有效安装。已经Tested with 5.4.1版本的wordpress。
Description

Eliminate Render-blocking Javascript in above-the-fold content with Async Javascript.

Render-blocking Javascript prevents above-the-fold content on your page from being rendered until the javascript has finished loading. This can impact on your page speed and ultimately your ranking within search engines. It can also impact your user’s experience.

Async JavaScript gives you full control of which scripts to add an ‘async’ or ‘defer’ attribute to or to exclude to help increase the performance of your WordPress website.