react native flatlist use index as key

1<FlatList 
2  data={[{name: 'a'}, {name: 'b'}]} 
3  renderItem={
4    ({item}) => <Text>{item.name}</Text>
5  } 
6  keyExtractor={(item, index) => index.toString()}
7/>
8

1 keyExtractor={(item, index) => index.toString()}