whyCleanupRunAfterRerender.js

function Detail() {
  const [x, addOneToX] = React.useReducer(x=>x+1,0);
  const [, forceUpdate] = React.useReducer(x=>x+1,0);
  console.log('render: ', x);
  React.useEffect(() => {
    console.log('effect: ', x);
    return function() {
      console.log('cleanup: ', x);
    }
  }, [x]);
  return (
    <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
      <Text>Detail!</Text>
      <Button title="x" onPress={addOneToX} />
      <Button title="forceupdate" onPress={forceUpdate} />
    </View>
  );
}