conditionally load javascript & CSS for do_action() calls from plugin

And…. the answer was actually correct, if you are using the correct functions. As Milo pointed out, it’s wp_enqueue_script not scripts.

add_action('wp_footer', 'print_my_script');
function print_my_script() {
    if(did_action('my_custom_action')) {
        wp_enqueue_script('listings');
        wp_enqueue_script('isotope');
    } 
}

Hopefully this helps someone else in need!