If you need to load an enqueued script asynchronously in WordPress, or modify the <script> element in any other way, you can use code like the following:

my_async_script.php

/**
 * Add async attributes to enqueued scripts where needed.
 * The ability to filter script tags was added in WordPress 4.1 for this purpose.
 * http://scottnelle.com/756/async-defer-enqueued-wordpress-scripts/
 */
function my_async_scripts( $tag, $handle, $src ) {
    // the handles of the enqueued scripts we want to async
    $async_scripts = array( 'some-script', 'another-script' );

    if ( in_array( $handle, $async_scripts ) ) {
        return '<script type="text/javascript" src="' . $src . '" async="async"></script>' . "\n";
    }

    return $tag;
}
add_filter( 'script_loader_tag', 'my_async_scripts', 10, 3 );