example.js

var kreditData = {
    code: 'AzNjE5NzA',
    items: [
        {
            title: "Apple iPhone 6+ 128Gb space gray",
            qty: 1,
            price: "37400.00"
        }
    ]
};
(function ($) {
    $(document).ready(function () {
        $('.link_kredit > img').on('click', function () {
            kVK.openWidget(kreditData);
        });
        $('#quantity').on('change', function () {
            kreditData.items[0]['qty'] = parseInt($(this).val());
        });
    });
})(jQuery);