FlashList – make your lists faster now

Fořt describes FlatList performance problems on low-end Android devices, including low frame rates and large blank areas. RecyclerListView can be fast and flexible, but he says its broad API is harder to learn and dynamic item heights can cause gaps or overlap during the first render.

FlashList aims for high UI and JavaScript frame rates, fewer blank areas, and an API that is easy to adopt. Its API resembles FlatList, while its recycling pool reuses cells as users scroll instead of repeatedly creating new ones. Fořt says this can avoid creating new JavaScript objects and native views when only an item’s content changes.

Fořt explains that estimated item sizes can misplace items when their actual heights differ, leading to gaps or overlap. FlashList uses a native view to correct layout during the first render and supports dynamic heights. In a Moto G10 comparison, FlatList averaged 11.8 JavaScript FPS and 44 UI FPS, with nearly two seconds of JavaScript thread lock; FlashList averaged 49 and 58 FPS, with no such lock.

In a demo, Fořt replaces FlatList with FlashList and sets an estimated item size of 150 based on the sample data. He warns that a changing key on a top-level item component forces it to unmount and remount, defeating recycling; removing the key improves the benchmark results. The demo also shows a benchmark hook that reports frame rate and blank-area metrics.

Fořt says Shopify’s shop app changed from nearly unusable with FlatList to snappy with only minimal blank cells on a low-end Android device. He reports FlashList is used across Shopify, Mobile, Shop, Inbox, and POS, and says Shopify considers it production-ready based on testing and community feedback.