WordPress - Make `wp_enqueue`'d scripts async.

WP-async-enqued.php

<?php

/**
 * Set all enqueued scripts except jQuery to include the `async` attribute.
 *
 * @see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#Attributes
 */
add_filter('script_loader_tag', function ($tag, $handle) {
    if ( 'jquery' !== $handle )
        return $tag;
    return str_replace( ' src', ' async="async" src', $tag );
}, 99, 2);