How to use add_action inside files included by theme's functions.php

Question

I've a functions.php inside my theme folder. The first line of functions.php is

require_once 'custom.php';

inside custom.php I have this simple code:

add_action('wp_print_scripts','add_js_vars');
function add_js_vars(){ 
    //some stuff here
}

The problem with the code above is that add_js_vars is not executed. If I move add_action('wp_print_scripts','add_js_vars'); inside themes functions.php everything works fine. I'm not able to understand what's the problem. Any ideas? Thanks for your help.

Answer 1

Just wrap you include(s) in a function and hook it to after_setup_theme hook.