loading javascript CDN with local fallback (not jQuery)

Question

I'm trying to modify this to register and enqueue a jQuery plugin from a CDN with local fallback.

However, when the URL fails (or if I give it a fake url) Firebug receives 2 aborted calls to the URL before loading the local fallback. With the jQuery fallback like the link, it only receives 1 aborted call.

It looks like it is trying to load the script twice before using the fallback.

function gavsiu_scripts() {
  if (is_single() && comments_open() && get_option('thread_comments') || is_page_template('page-contact.php')) {
    wp_register_script('jquery_validate', '//ajax.aspnetcdn.com/ajax/jquery.validate/1.11.0/jquery.validate.min.js', array('jquery'), null, false);
    add_filter('script_loader_src', 'gavsiu_jquery_validate_local_fallback', 10, 2);
    wp_enqueue_script('jquery_validate');
  }
}

add_action('wp_enqueue_scripts', 'gavsiu_scripts', 100);

function gavsiu_jquery_validate_local_fallback($src, $handle) {
  static $add_fallback = false;

  if ($add_fallback) {
    echo '<script>if(typeof $().validate == \'undefined\') document.write(\'<script src="' . get_template_directory_uri() . '/js/jquery.validate.min.js"><\/script>\')</script>' . "\n";
    $add_fallback = false;
  }

  if ($handle === 'jquery_validate') {
    $add_fallback = true;
  }

  return $src;
}

Answer 1

The order of your hooks will cause issues since your loading gavsiu_scripts via wp_enqueue_scripts and your using it to also load your fallback function using script_loader_src.

As far as I can tell the only good way to load a fallback script is to not use wp_enqueue_scripts and instead just load your js into wp_head or wp_footer, as per the example in your link.