EV
Elena Vasquez
April 22, 2026 · 10 min read
Why Functions exist
Functions let you customize discounts, shipping, and payment logic with server-side code that runs inside Shopify's checkout — replacing the checkout-script apps that Checkout Extensibility retired.
They're fast, versioned, and predictable, which makes them a far safer foundation than the app stack they replace.
A concrete example
A tiered wholesale discount that used to require a checkout-script app becomes a small, testable Function you own in your repo.
Because Functions run within Shopify's limits, you get consistent behavior without adding checkout latency.
Topics
shopify functionscheckout customizationshopify plus
