I tried this : http://themes.simplethemes.com/skeleton/tutorials/how-to-add-custom-css-and-javascript-using-a-child-theme/
And I added this in my functions.php inside my child theme directory :
function my_custom_javascript() {
wp_enqueue_style('additional', get_stylesheet_directory_uri().'/js/additional.js', array('jquery'), '1.0', 'screen, projection');
}
add_filter('child_add_javascripts','my_custom_javascript');
Of course I have created the file skeleton_childtheme/js/additional.js
but it doesn't do anything and my additional.js is not loaded. Any idea? :(