function js_async_attr($tag)
{
    if ( !is_user_logged_in() )
    {
        $scripts_to_exclude = array('script1.js', 'script2.js', 'script3.js');
        foreach($scripts_to_exclude as $exclude_script)
        {
            if(true == strpos($tag, $exclude_script ))
            return $tag;
        }
        return str_replace( ' src', ' defer async src', $tag );
    }
}
add_filter( 'script_loader_tag', 'js_async_attr', 10 );