js

const request = new PaymentRequest(methodData, details, options);
// Async update to details
request.onshippingaddresschange = (ev) => {
  ev.updateWith(checkShipping(request));
};
// Sync update to the total
request.onshippingoptionchange = (ev) => {
  const shippingOption = shippingOptions.find(
    (option) => option.id === request.id,
  );
  const newTotal = {
    currency: "USD",
    label: "Total due",
    value: calculateNewTotal(shippingOption),
  };
  ev.updateWith({ ...details, total: newTotal });
};
async function checkShipping(request) {
  try {
    const json = request.shippingAddress.toJSON();

    await ensureCanShipTo(json);
    const { shippingOptions, total } = await calculateShipping(json);

    return { ...details, shippingOptions, total };
  } catch (err) {
    return { ...details, error: `Sorry! we can't ship to your address.` };
  }
}