Change template_directory to use a CDN path

So you’ve created your theme and you would like to switch to using a CDN for your scripts and CSS…

Add this to your functions.php and replace the YOUR-SITE with the urls of the website and the CDN.

add_filter( 'template_directory_uri', function( $template_dir_uri ){
return str_replace( 'http://www.YOUR-SITE.co.uk/', '//cdn.YOUR-SITE.co.uk/', $template_dir_uri );
});