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

reactnative.dev/docs/flatlist#example の 2 つ目の例から始め、関連付けられた issue 1529 と pull request 2634 を読んで、これまでの経緯を確認してください。extraData がある場合とない場合の例の動作を比較し、ドキュメントを変更する前に現在の FlatList に関するガイダンスを確認してください。完了の条件は、extraData が必要になる場合を例と説明で正確に示せていることです。