如何使用bigcommerce的checkout-sdk-js在结账中添加新的自定义字段？

import { createCheckoutButton } from '@bigcommerce/checkout-sdk';

const buttonContainer = document.getElementById('checkout-button-container');

createCheckoutButton(buttonContainer, {
  containerId: 'checkout-button',
});

import { getCheckout } from '@bigcommerce/checkout-sdk';

const buttonContainer = document.getElementById('checkout-button-container');

createCheckoutButton(buttonContainer, {
  containerId: 'checkout-button',
  onReady: async (state) => {
    const checkout = await getCheckout(state.data.getCheckoutUrl);

    // 在这里可以对checkout对象进行操作，添加自定义字段等
  },
});

checkout.updateBillingAddress({
  customFields: [
    {
      name: 'custom_field_name',
      value: 'custom_field_value',
    },
  ],
});