(function($) {
    'use strict';
    
    wp.customize.bind('ready', function() {
        $('.sortable-posts-list').sortable({
            update: function(event, ui) {
                var $list = $(this);
                var postIds = [];
                $list.find('li').each(function() {
                    postIds.push($(this).data('post-id'));
                });
                var $input = $list.closest('.customize-control').find('input[type="hidden"]');
                $input.val(postIds.join(',')).trigger('change');
            }
        });
    });
})(jQuery);