Add example with side effect in render got triggered directly (#38830)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/38830

Changelog:
[Internal] - Add example with side effect in render got triggered directly

Reviewed By: rshest

Differential Revision: D48055836

fbshipit-source-id: 8bf596165741bde93cf44cd96b93fb2efaea1b13

packages/rn-tester/js/examples/Performance/performanceComparisonExamples/EffectInRenderExample.js

@@ -0,0 +1,131 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict-local
+ * @format
+ * @oncall react_native
+ */
+
+'use strict';
+
+import type {ItemDataType} from '../components/itemData';
+
+import * as React from 'react';
+import {useState, useEffect, useCallback, StrictMode} from 'react';
+import {Text} from 'react-native';
+import {generateRandomItems} from '../components/itemData';
+import ItemList from '../components/ItemList';
+
+const TIMEOUT = 500;
+const FETCH_COUNT = 250;
+const ItemListMemo = React.memo(ItemList);
+
+function ItemFetcherBadExample(props: {
+  onFetched: (items: ItemDataType[]) => void,
+  count: number,
+}): React.Node {
+  const {onFetched, count} = props;
+  const fetchMoreItems = async (
+    itemsCount: number,
+  ): Promise<ItemDataType[]> => {
+    return new Promise(resolve => {
+      setTimeout(() => {
+        resolve(generateRandomItems(itemsCount));
+      }, TIMEOUT);
+    });
+  };
+
+  fetchMoreItems(count).then((items: ItemDataType[]) => {
+    onFetched(items);
+  }, console.error);
+}
+
+function ItemFetcherGoodExample(props: {
+  onFetched: (items: ItemDataType[]) => void,
+  count: number,
+}): React.Node {
+  const {onFetched, count} = props;
+  useEffect(() => {
+    const fetchMoreItems = async (
+      itemsCount: number,
+    ): Promise<ItemDataType[]> => {
+      return new Promise(resolve => {
+        setTimeout(() => {
+          resolve(generateRandomItems(itemsCount));
+        }, TIMEOUT);
+      });
+    };
+
+    fetchMoreItems(count).then((items: ItemDataType[]) => {
+      onFetched(items);
+    }, console.error);
+  }, [onFetched, count]);
+}
+
+const ItemFetcherBadExampleMemo = React.memo(ItemFetcherBadExample);
+const ItemFetcherGoodExampleMemo = React.memo(ItemFetcherGoodExample);
+function EffectInRenderBadExample(): React.Node {
+  const [visibleItems, setVisibleItems] = useState<ItemDataType[]>([]);
+  const [fetchedItems, setFetchedItems] = useState<ItemDataType[]>([]);
+  const onMoreItemFetched = useCallback(
+    (items: ItemDataType[]) => {
+      setFetchedItems(items);
+    },
+    [setFetchedItems],
+  );
+
+  if (fetchedItems.length > 0) {
+    setVisibleItems(visibleItems.concat(fetchedItems));
+    setFetchedItems([]);
+  }
+
+  return (
+    <StrictMode>
+      <Text>{`Items count in list: ${visibleItems.length}`}</Text>
+      <ItemFetcherBadExampleMemo
+        onFetched={onMoreItemFetched}
+        count={FETCH_COUNT}
+      />
+      <ItemListMemo data={visibleItems} />
+    </StrictMode>
+  );
+}
+
+function EffectInRenderGoodExample(): React.Node {
+  const [visibleItems, setVisibleItems] = useState<ItemDataType[]>([]);
+  const [fetchedItems, setFetchedItems] = useState<ItemDataType[]>([]);
+  const onMoreItemFetched = useCallback(
+    (items: ItemDataType[]) => {
+      setFetchedItems(items);
+    },
+    [setFetchedItems],
+  );
+
+  if (fetchedItems.length > 0) {
+    setVisibleItems(visibleItems.concat(fetchedItems));
+    setFetchedItems([]);
+  }
+
+  return (
+    <StrictMode>
+      <Text>{`Items count in list: ${visibleItems.length}`}</Text>
+      <ItemFetcherGoodExampleMemo
+        onFetched={onMoreItemFetched}
+        count={FETCH_COUNT}
+      />
+      <ItemListMemo data={visibleItems} />
+    </StrictMode>
+  );
+}
+
+export default {
+  title:
+    'Directly trigger side effect in render may run multiple times and cause error state or re-renders',
+  description:
+    'Trigger a side effect in render method without using effect hook in <StrictMode>. This will force render component two times, and the side effect in bad example caused append items to the list two times unexpectedly.',
+  Bad: EffectInRenderBadExample,
+  Good: EffectInRenderGoodExample,
+};

packages/rn-tester/js/examples/Performance/performanceComparisonExamples/index.js

@@ -14,3 +14,4 @@ export {default as ReRenderWithObjectPropExample} from './ReRenderWithObjectProp
 export {default as SetStateInWrongEffectExample} from './SetStateInWrongEffectExample';
 export {default as RenderOffscreenContentExample} from './RenderOffscreenContentExample';
 export {default as NotMemoizeExpensiveTaskExample} from './NotMemoizeExpensiveTaskExample';
+export {default as EffectInRenderExample} from './EffectInRenderExample';