BigCommerce Checkout Customization

Before writing code

Fetch live docs:

1. Fetch https://developer.bigcommerce.com/docs/storefront/cart-checkout/checkout-sdk for Checkout SDK
2. Web-search site:developer.bigcommerce.com checkout api for Checkout API reference
3. Web-search bigcommerce embedded checkout headless for embedded checkout patterns

Checkout Architecture

Three Approaches

Checkout SDK

What It Is

A JavaScript SDK for customizing the native BigCommerce checkout:

• Renders checkout UI in a target DOM element
• Provides methods to interact with checkout state
• Fires events for checkout lifecycle
• Available as @bigcommerce/checkout-sdk npm package

Installation

npm install @bigcommerce/checkout-sdk

Core Methods

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

const service = createCheckoutService();

// Load checkout
await service.loadCheckout(checkoutId);

// Get current state
const state = service.getState();
const checkout = state.data.getCheckout();

// Update shipping address
await service.updateShippingAddress(address);

// Select shipping option
await service.selectShippingOption(optionId);

// Apply coupon
await service.applyCoupon(code);

// Submit order
await service.submitOrder(orderPayload);

State Selectors

The state object provides selectors:

• getCheckout() — full checkout data
• getCart() — cart items and totals
• getCustomer() — customer info
• getShippingAddress() — shipping address
• getBillingAddress() — billing address
• getShippingOptions() — available shipping methods
• getPaymentMethods() — available payment methods
• getOrder() — completed order

Checkout Events

Subscribe to state changes:

service.subscribe(state => {
  const checkout = state.data.getCheckout();
  // React to checkout state changes
});

Embedded Checkout

How It Works

Embed BigCommerce's checkout in an external site via iframe:

1. Create a cart via the Server-to-Server Cart API
2. Generate a checkout URL (from the cart's redirect_urls.checkout_url)
3. Embed the URL in an iframe on your site
4. Listen for postMessage events from the iframe

Setup

Include the Embedded Checkout script:

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

embedCheckout({
  url: checkoutUrl,
  containerId: 'checkout-container',
  onComplete: () => { /* order placed */ },
  onError: (error) => { /* handle error */ },
  onFrameLoad: () => { /* checkout loaded */ },
});

Requirements

• HTTPS on your domain
• Configure "Trusted Domains" in BigCommerce admin
• Set X-Frame-Options and CSP headers to allow embedding

Server-Side Checkout API

Cart to Checkout Flow

1. Create Cart: POST /v3/carts with line items
2. Add Billing Address: POST /v3/checkouts/{id}/billing-address
3. Add Consignment (Shipping): POST /v3/checkouts/{id}/consignments
4. Select Shipping Option: PUT /v3/checkouts/{id}/consignments/{consignmentId}
5. Create Order: POST /v3/checkouts/{id}/orders
6. Process Payment: POST /v3/payments (via Payments API)

Key Endpoints

Checkout Customization in Stencil

Theme Template

Checkout uses templates/pages/checkout.html with special handling:

• Uses the empty layout (minimal wrapper)
• Checkout UI is primarily JavaScript-rendered
• Limited template customization compared to other pages

Checkout JS Customization

Override checkout JavaScript for UI modifications:

• Fork the open-source checkout: github.com/bigcommerce/checkout-js
• Build custom React checkout components
• Deploy as a custom checkout script

Best Practices

• Use Embedded Checkout for headless — avoids PCI scope expansion
• Use the Checkout SDK for programmatic control
• Always use HTTPS for checkout flows
• Handle payment failures gracefully with clear error messages
• Test the full checkout flow with real payment sandbox credentials
• Support guest checkout and registered customer checkout
• Validate all addresses server-side
• Handle coupon edge cases (expired, minimum spend, etc.)

Fetch the Checkout SDK docs and BigCommerce Checkout API reference for exact method signatures, state structure, and configuration options before implementing.