Making a Shopify storefront widget feel instant

A storefront widget is a guest in someone else’s house. It has to be fast, it has to not move the page around, and it has to fail quietly.

The biggest win was rendering server-side and shipping a tiny hydration script instead of a framework. The widget is ~6KB and reserves its space before any data arrives, so CLS stays at zero.

The second win was caching at the edge. Chart and feed data rarely change, so a stale-while-revalidate policy keeps the CDN hit rate near 98% and the origin almost idle.

Performance isn’t a feature you add at the end — it’s a budget you defend from the first commit.