Fix useColorScheme subscription lifecycle

packages/react-native-web/src/exports/useColorScheme/__tests__/index-test.js

@@ -0,0 +1,38 @@
+/**
+ * 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
+ */
+
+import * as React from 'react';
+import { render } from '@testing-library/react';
+import Appearance from '../../Appearance';
+import useColorScheme from '..';
+
+describe('useColorScheme', () => {
+  test('keeps its subscription active across rerenders', () => {
+    const remove = jest.fn();
+    const addChangeListener = jest
+      .spyOn(Appearance, 'addChangeListener')
+      .mockReturnValue({ remove });
+
+    function Component({ label }): React.Node {
+      const colorScheme = useColorScheme();
+      return <div>{`${label}:${colorScheme}`}</div>;
+    }
+
+    const { rerender, unmount } = render(<Component label="first" />);
+    expect(addChangeListener).toHaveBeenCalledTimes(1);
+    expect(remove).not.toHaveBeenCalled();
+
+    rerender(<Component label="second" />);
+    expect(addChangeListener).toHaveBeenCalledTimes(1);
+    expect(remove).not.toHaveBeenCalled();
+
+    unmount();
+    expect(remove).toHaveBeenCalledTimes(1);
+  });
+});

packages/react-native-web/src/exports/useColorScheme/index.js

@@ -25,7 +25,7 @@ export default function useColorScheme(): ColorSchemeName {
     }
     const { remove } = Appearance.addChangeListener(listener);
     return remove;
-  });
+  }, []);
 
   return colorScheme;
 }