Async an arrayed list of JavaScript files with script_loader_tag

async.php

/**
 * Function to Async an arrayed list of JavaScript files.
 *
 * @param $tag
 * @param $handler
 * @param $src
 *
 * @return mixed
 */
function async_scripts( $tag, $handler, $src ) {
	
	/**
	 * An array of JavaScripts files. The value should be the filename.
	 */
	$scripts = array(
		'script_one.js',
		'script_two.js'
	);
	
	/**
	 * Loop through each file in the $scripts array and add an async option.
	 */
	foreach ( $scripts as $script ) {

		if ( true == strpos( $tag, $script ) )
		return str_replace( ' src', ' async src', $tag );
	}

	return $tag;

}
add_filter( 'script_loader_tag', 'async_scripts', 10, 3 );