Try to code something as below
var addItemToCart = function (form, addToCartButton) {
var $form = $(form),
$qty = $form.find('input[name="Quantity"]');
if ($qty.length === 0 || isNaN($qty.val()) || parseInt($qty.val(), 10) === 0) {
$qty.val('1');
}
var data = $form.serialize();
var bundleDataCtr = '';
data += '&' + User.CSRFTokenName + '=' + User.CSRFTokenValue;
if (addToCartButton !== null && addToCartButton !== '') {
bundleDataCtr = addToCartButton.closest('.bundle-data-container');
if (bundleDataCtr.attr('data-bundle-child-pids') !== undefined) {
data += '&' + 'childPids' + '=' + bundleDataCtr.attr('data-bundle-child-pids');
}
}
return TPromise.resolve($.ajax({
type: 'POST',
url: util.ajaxUrl(Urls.addProduct),
data: data
}));
};