gistfile1.js

var ajax = {
    success: function (data) {
        if (!data) {
            alert('Ошибка, сервера.');
            return;
        }

        if (data.status == 'success') {

            var shippingMethods = 'shipping_methods',
                paymentMethods  = 'payment_methods',
                $shippingStep   = $('#checkout-step-shipping_method'),
                $paymentStep    = $('#checkout-step-payment'),
                $reviewTable    = $('#checkout-review-load'),
                $couponBlock    = $('#couponBlock');

            if (data.content == undefined) {
                alert('Контент не пришел');
                return;
            }

            if (data.content[shippingMethods]) {
                $shippingStep.html(data.content[shippingMethods]);
                checkoutObj.initShippingForm();
            }

            if (data.content[paymentMethods]) {
                $paymentStep.html(data.content[paymentMethods]);
                checkoutObj.initPaymentMethods();
            }

            if (data.content.cart) {
                $reviewTable.html(data.content.cart);
            }

            if (data.content.coupon) {
                $couponBlock.replaceWith(data.content.coupon);
                coupon.init(checkoutObj);
            }


        } else if ((data.status === 'error') && data.message) {
            $info.html(data.message).addClass('error');
        }
    }
};