How to pass email and address to checkout?

[julianCast]

 var client = ShopifyBuy.buildClient({
          domain: 'myshop.myshopify.com',
          storefrontAccessToken: '12345'
        })

As you can see below, client.checkout contains updateEmail and updateShippingAddress.

How can I get checkoutId so I can use those functions or there is an easier function to do this ? Thanks!

If I hardcoded use the checkout.id, no changes are shown in the checkout.

client.checkout.updateEmail(checkoutId, 'test@gmail.com').then(c => {
      console.log(c) // This is shown in the console but the email won't change
    })

[julianCast]

I think the library (buy-button.js) is not prepared to allow an update, so this is my workaround.

MY COMPONENT

const cart = UIShopify.components.cart[0]
 cart.updater.updateConfig({
          options: {
            email:email
            shippingAddress: shippingAddress 
          }
        })

buy-button.js BEFORE FIX

_proto.onCheckout = function onCheckout() {
      this._userEvent('openCheckout');

      this.props.tracker.track('Open cart checkout', {});
      this.checkout.open(this.model.webUrl);
    }

buy-button.js AFTER FIX

_proto.onCheckout = function onCheckout()
     {
       this._userEvent('openCheckout');

       this.props.tracker.track('Open cart checkout', {});

       let items = this.lineItemCache.map(i => { return { variantId: i.variant.id, quantity: i.quantity } });
       var input = {
         lineItems: items,
         shippingAddress: this.config.shippingAddress,
         email: this.config.email
       }

       var checkoutWindow = window.open('', 'checkout', this.checkout.params);

       this.props.client.checkout.create(input).then(function (checkout)
       {
         checkoutWindow.location = checkout.webUrl;
       });
     }