How to Fix “TypeError: $(….).chained is not function” error in WordPress custom page?

Solution:

This happens because the “Chained Selects” plugin source is not included:

function enqueue_stuff(){
wp_enqueue_script(‘chainedjs’, ‘https://raw.githubusercontent.com/tuupola/jquery_chained/master/jquery.chained.remote.min.js’, array(‘jquery’), false, true);
}
add_action(‘wp_enqueue_scripts’, ‘enqueue_stuff’);