Devlog

checkout-extensions.md — VIEW

$ cat ~/devlog/checkout-extensions.md

Checkout & theme extensions without breaking the store

5 min readCheckout UIFunctionsTheme
fig.3 — the most expensive page you own
fig.3 — the most expensive page you own

Checkout is the one page you cannot afford to slow down. Extensions let you add to it without touching Liquid or forking the theme.

Pick the right surface

  • Checkout UI extensions — blocks inside checkout and thank-you pages.
  • Shopify Functions — backend logic: discounts, delivery and payment customisation.
  • Theme app extensions — app blocks merchants drag into any theme.

Functions run as WebAssembly

Your code compiles to wasm and runs inside Shopify's infrastructure, next to the cart. No servers, no cold starts, but a strict execution budget — keep the logic lean.

extensions/upsell-block/shopify.extension.toml
api_version = "2026-07"

[[extensions]]
type = "ui_extension"
name = "upsell-block"
handle = "upsell-block"

[[extensions.targeting]]
target = "purchase.thank-you.block.render"
module = "./src/ThankYou.jsx"

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