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function footer_enqueue_scripts() {
 remove_action('wp_head', 'wp_print_scripts');
 remove_action('wp_head', 'wp_print_head_scripts', 9);
 remove_action('wp_head', 'wp_enqueue_scripts', 1);
 add_action('wp_footer', 'wp_print_scripts', 5);
 add_action('wp_footer', 'wp_enqueue_scripts', 5);
 add_action('wp_footer', 'wp_print_head_scripts', 5);
}
add_action('after_setup_theme', 'footer_enqueue_scripts');

function add_async_attribute($tag, $handle) {
   // agregar los handles de los scripts en el array
   $scripts_to_async = array('script-name', 'script-name2');

   foreach($scripts_to_async as $async_script) {
      if ($async_script === $handle) {
         return str_replace(' src', ' async defer src', $tag);
      }
   }
   return $tag;
}
add_filter('script_loader_tag', 'add_async_attribute', 10, 2);