Adding onViewableItemsChanged to SectionList changes the items passed to each section's keyExtractor

[bhandanyan-nomad]

Description

We wrote a SectionList component where each section defines it's own keyExtractor. One of the sections uses a key from a nested object in each item in the section. It broke when we wanted to add visibility tracking to the section list, and it seems like the section objects are being run through the keyExtractor but only when onViewableItemsChanged prop is provided.

I expect that only items within each section should be run through the section's keyExtractor function, and that the behavior is consistent regardless of what props are provided.

Steps to reproduce

1. Open expo snack linked below
2. Run it on android or iOS device and observe it works
3. Uncomment the onViewableItemsChanged line from the SectionList and observe the break

React Native Version

0.75.3

Affected Platforms

Runtime - Android, Runtime - iOS

Output of npx react-native info

See expo snack for reproduction

Stacktrace or Logs

Cannot read property 'id' of undefined

Reproducer

https://snack.expo.dev/V1Ad0VTld860Zdt8n-qb7

Screenshots and Videos

[softgenicsShubham]

@bhandanyan-nomad, I tried your reproducer, it needs slight modification.

import React from 'react';
import { View, Text, SafeAreaView, StyleSheet, SectionList, SectionListData } from 'react-native';

interface Item {
  id: string;
  title: string;
  nested?: {
    id: string;
  };
}

interface SectionData extends SectionListData<Item> {
  title: string;
  data: Item[];
}

const sections: SectionData[] = [
  {
    title: 'Active',
    data: [
      { id: '1', title: 'hello', nested: { id: '2' } },
      { id: '2', title: 'hello 2', nested: { id: '1' } },
    ],
  },
  {
    title: 'Closed',
    data: [
      { id: '4', title: 'hello', nested: { id: '3' } },
      { id: '3', title: 'hello 2', nested: { id: '4' } },
    ],
  },
];

interface ViewableItemsChangedProps {
  viewableItems: Array<{
    item: Item;
    key: string;
    isViewable: boolean;
    index: number | null;
    section?: SectionListData<Item>;
  }>;
}

const onViewableItemsChanged = ({ viewableItems }: ViewableItemsChangedProps) => {
  viewableItems.forEach(({ item }) => {
    // console.log({ item });
  });
};

export default function App() {
  return (
    <SafeAreaView style={styles.container}>
      <SectionList
        sections={sections}
        keyExtractor={(item) => {
          console.log('item', item)
          return item.nested?.id || item.id
        }}
        renderSectionHeader={({ section }) => (
          <View style={{ paddingVertical: 16 }}>
            <Text>{section.title}</Text>
          </View>
        )}
        renderItem={({ item }) => (
          <Text>Title: {item.title} NestedId: {item.nested?.id ?? 'No Nested ID'}</Text>
        )}
        onViewableItemsChanged={onViewableItemsChanged}
      />
    </SafeAreaView>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    backgroundColor: '#ecf0f1',
    padding: 8,
  },
});

[bhandanyan-nomad]

@softgenicsShubham your code works but it doesn't really get at the root of the issue, which is that my code which runs fine without onViewableItemsChanged suddenly crashes as soon as it is provided. I'd like to figure out what's expected here and why. If it is expected that the sections are sent through the keyExtractor, I think the typescript types need to be updated to reflect that