View file vtposter/assets/js/pages/ui/sortable-nestable.js

$(function () {
    $('.dd').nestable();

    $('.dd').on('change', function () {
        var $this = $(this);
        var serializedData = window.JSON.stringify($($this).nestable('serialize'));

        $this.parents('div.body').find('textarea').val(serializedData);
    });
});