Example showing need for FlatList extraData prop is misleading

Basically https://github.com/react/react-native-website/issues/1529 from 2019 which was closed due to inactivity.

Related: https://github.com/react/react-native-website/pull/2634 which attempted to address this but unfortunately received no attention.

Description

The second example at https://reactnative.dev/docs/flatlist#example is introduced with

By passing extraData={selectedId} to FlatList we make sure FlatList itself will re-render when the state changes. Without setting this prop, FlatList would not know it needs to re-render any items because it is a PureComponent and the prop comparison will not show any changes.

But if you delete the extraData prop everything works fine. Since renderItem closes over selectedId, it is recreated whenever selectedId changes (or on every single render if the react compiler is disabled), hence FlatList receives a new prop and re-renders properly as you'd expect.

Which makes me wonder: is there ever a need for extraData? Was it once necessary (perhaps in class component days, or old react native architecture) and is no longer needed?

I'm struggling to think of a scenario in which it's needed, other than an escape hatch for syncing with something outside react, or to opt back in to reactivity after making manual memoizations.

Currently the docs suggest it's necessary to make basic reactivity work, which is confusing.

Documentation version

0.87

Inizia dal secondo esempio all’indirizzo reactnative.dev/docs/flatlist#example, poi leggi l’issue 1529 e la pull request 2634 collegate per esaminare il contesto precedente. Confronta il comportamento dell’esempio con e senza extraData e verifica le indicazioni attuali su FlatList prima di modificare la documentazione. Il lavoro è completato quando l’esempio e la spiegazione descrivono accuratamente quando è necessario extraData.