useSyncExternalStoreShared-test.js

/**
 * 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.
 *
 * @emails react-core
 */

'use strict';

let useSyncExternalStore;
let useSyncExternalStoreWithSelector;
let React;
let ReactDOM;
let ReactDOMClient;
let Scheduler;
let act;
let useState;
let useEffect;
let useLayoutEffect;
let assertLog;
let originalError;

// This tests shared behavior between the built-in and shim implementations of
// of useSyncExternalStore.
describe('Shared useSyncExternalStore behavior (shim and built-in)', () => {
  beforeEach(() => {
    jest.resetModules();
    if (gate(flags => flags.enableUseSyncExternalStoreShim)) {
      // Test the shim against React 17.
      jest.mock('react', () => {
        return jest.requireActual(
          __DEV__
            ? 'react-17/umd/react.development.js'
            : 'react-17/umd/react.production.min.js',
        );
      });
      jest.mock('react-dom', () =>
        jest.requireActual(
          __DEV__
            ? 'react-dom-17/umd/react-dom.development.js'
            : 'react-dom-17/umd/react-dom.production.min.js',
        ),
      );
      // Because React 17 prints extra logs we need to ignore them.
      originalError = console.error;
      console.error = jest.fn();
    }
    React = require('react');
    ReactDOM = require('react-dom');
    ReactDOMClient = require('react-dom/client');
    Scheduler = require('scheduler');
    useState = React.useState;
    useEffect = React.useEffect;
    useLayoutEffect = React.useLayoutEffect;
    const InternalTestUtils = require('internal-test-utils');
    assertLog = InternalTestUtils.assertLog;
    const internalAct = require('internal-test-utils').act;

    // The internal act implementation doesn't batch updates by default, since
    // it's mostly used to test concurrent mode. But since these tests run
    // in both concurrent and legacy mode, I'm adding batching here.
    act = cb => internalAct(() => ReactDOM.unstable_batchedUpdates(cb));
    if (gate(flags => flags.source)) {
      // The `shim/with-selector` module composes the main
      // `use-sync-external-store` entrypoint. In the compiled artifacts, this
      // is resolved to the `shim` implementation by our build config, but when
      // running the tests against the source files, we need to tell Jest how to
      // resolve it. Because this is a source module, this mock has no affect on
      // the build tests.
      jest.mock('use-sync-external-store/src/useSyncExternalStore', () =>
        jest.requireActual('use-sync-external-store/shim'),
      );
    }
    useSyncExternalStore =
      require('use-sync-external-store/shim').useSyncExternalStore;
    useSyncExternalStoreWithSelector =
      require('use-sync-external-store/shim/with-selector').useSyncExternalStoreWithSelector;
  });
  afterEach(() => {
    if (gate(flags => flags.enableUseSyncExternalStoreShim)) {
      console.error = originalError;
    }
  });
  function Text({text}) {
    Scheduler.log(text);
    return text;
  }
  function createRoot(container) {
    // This wrapper function exists so we can test both legacy roots and
    // concurrent roots.
    if (gate(flags => !flags.enableUseSyncExternalStoreShim)) {
      // The native implementation only exists in 18+, so we test using
      // concurrent mode. To test the legacy root behavior in the native
      // implementation (which is supported in the sense that it needs to have
      // the correct behavior, despite the fact that the legacy root API
      // triggers a warning in 18), write a test that uses
      // createLegacyRoot directly.
      return ReactDOMClient.createRoot(container);
    } else {
      // This ReactDOM.render is from the React 17 npm module.
      ReactDOM.render(null, container);
      return {
        render(children) {
          ReactDOM.render(children, container);
        },
      };
    }
  }
  function createExternalStore(initialState) {
    const listeners = new Set();
    let currentState = initialState;
    return {
      set(text) {
        currentState = text;
        ReactDOM.unstable_batchedUpdates(() => {
          listeners.forEach(listener => listener());
        });
      },
      subscribe(listener) {
        listeners.add(listener);
        return () => listeners.delete(listener);
      },
      getState() {
        return currentState;
      },
      getSubscriberCount() {
        return listeners.size;
      },
    };
  }
  it('basic usage', async () => {
    const store = createExternalStore('Initial');
    function App() {
      const text = useSyncExternalStore(store.subscribe, store.getState);
      return React.createElement(Text, {
        text: text,
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog(['Initial']);
    expect(container.textContent).toEqual('Initial');
    await act(() => {
      store.set('Updated');
    });
    assertLog(['Updated']);
    expect(container.textContent).toEqual('Updated');
  });
  it('skips re-rendering if nothing changes', async () => {
    const store = createExternalStore('Initial');
    function App() {
      const text = useSyncExternalStore(store.subscribe, store.getState);
      return React.createElement(Text, {
        text: text,
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog(['Initial']);
    expect(container.textContent).toEqual('Initial');

    // Update to the same value
    await act(() => {
      store.set('Initial');
    });
    // Should not re-render
    assertLog([]);
    expect(container.textContent).toEqual('Initial');
  });
  it('switch to a different store', async () => {
    const storeA = createExternalStore(0);
    const storeB = createExternalStore(0);
    let setStore;
    function App() {
      const [store, _setStore] = useState(storeA);
      setStore = _setStore;
      const value = useSyncExternalStore(store.subscribe, store.getState);
      return React.createElement(Text, {
        text: value,
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog([0]);
    expect(container.textContent).toEqual('0');
    await act(() => {
      storeA.set(1);
    });
    assertLog([1]);
    expect(container.textContent).toEqual('1');

    // Switch stores and update in the same batch
    await act(() => {
      ReactDOM.flushSync(() => {
        // This update will be disregarded
        storeA.set(2);
        setStore(storeB);
      });
    });
    // Now reading from B instead of A
    assertLog([0]);
    expect(container.textContent).toEqual('0');

    // Update A
    await act(() => {
      storeA.set(3);
    });
    // Nothing happened, because we're no longer subscribed to A
    assertLog([]);
    expect(container.textContent).toEqual('0');

    // Update B
    await act(() => {
      storeB.set(1);
    });
    assertLog([1]);
    expect(container.textContent).toEqual('1');
  });
  it('selecting a specific value inside getSnapshot', async () => {
    const store = createExternalStore({
      a: 0,
      b: 0,
    });
    function A() {
      const a = useSyncExternalStore(store.subscribe, () => store.getState().a);
      return React.createElement(Text, {
        text: 'A' + a,
      });
    }
    function B() {
      const b = useSyncExternalStore(store.subscribe, () => store.getState().b);
      return React.createElement(Text, {
        text: 'B' + b,
      });
    }
    function App() {
      return React.createElement(
        React.Fragment,
        null,
        React.createElement(A, null),
        React.createElement(B, null),
      );
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog(['A0', 'B0']);
    expect(container.textContent).toEqual('A0B0');

    // Update b but not a
    await act(() => {
      store.set({
        a: 0,
        b: 1,
      });
    });
    // Only b re-renders
    assertLog(['B1']);
    expect(container.textContent).toEqual('A0B1');

    // Update a but not b
    await act(() => {
      store.set({
        a: 1,
        b: 1,
      });
    });
    // Only a re-renders
    assertLog(['A1']);
    expect(container.textContent).toEqual('A1B1');
  });

  // In React 18, you can't observe in between a sync render and its
  // passive effects, so this is only relevant to legacy roots
  // @gate enableUseSyncExternalStoreShim
  it(
    "compares to current state before bailing out, even when there's a " +
      'mutation in between the sync and passive effects',
    async () => {
      const store = createExternalStore(0);
      function App() {
        const value = useSyncExternalStore(store.subscribe, store.getState);
        useEffect(() => {
          Scheduler.log('Passive effect: ' + value);
        }, [value]);
        return React.createElement(Text, {
          text: value,
        });
      }
      const container = document.createElement('div');
      const root = createRoot(container);
      await act(() => root.render(React.createElement(App, null)));
      assertLog([0, 'Passive effect: 0']);

      // Schedule an update. We'll intentionally not use `act` so that we can
      // insert a mutation before React subscribes to the store in a
      // passive effect.
      store.set(1);
      assertLog([
        1,
        // Passive effect hasn't fired yet
      ]);
      expect(container.textContent).toEqual('1');

      // Flip the store state back to the previous value.
      store.set(0);
      assertLog([
        'Passive effect: 1',
        // Re-render. If the current state were tracked by updating a ref in a
        // passive effect, then this would break because the previous render's
        // passive effect hasn't fired yet, so we'd incorrectly think that
        // the state hasn't changed.
        0,
      ]);
      // Should flip back to 0
      expect(container.textContent).toEqual('0');
    },
  );
  it('mutating the store in between render and commit when getSnapshot has changed', async () => {
    const store = createExternalStore({
      a: 1,
      b: 1,
    });
    const getSnapshotA = () => store.getState().a;
    const getSnapshotB = () => store.getState().b;
    function Child1({step}) {
      const value = useSyncExternalStore(store.subscribe, store.getState);
      useLayoutEffect(() => {
        if (step === 1) {
          // Update B in a layout effect. This happens in the same commit
          // that changed the getSnapshot in Child2. Child2's effects haven't
          // fired yet, so it doesn't have access to the latest getSnapshot. So
          // it can't use the getSnapshot to bail out.
          Scheduler.log('Update B in commit phase');
          store.set({
            a: value.a,
            b: 2,
          });
        }
      }, [step]);
      return null;
    }
    function Child2({step}) {
      const label = step === 0 ? 'A' : 'B';
      const getSnapshot = step === 0 ? getSnapshotA : getSnapshotB;
      const value = useSyncExternalStore(store.subscribe, getSnapshot);
      return React.createElement(Text, {
        text: label + value,
      });
    }
    let setStep;
    function App() {
      const [step, _setStep] = useState(0);
      setStep = _setStep;
      return React.createElement(
        React.Fragment,
        null,
        React.createElement(Child1, {
          step: step,
        }),
        React.createElement(Child2, {
          step: step,
        }),
      );
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog(['A1']);
    expect(container.textContent).toEqual('A1');
    await act(() => {
      // Change getSnapshot and update the store in the same batch
      setStep(1);
    });
    assertLog([
      'B1',
      'Update B in commit phase',
      // If Child2 had used the old getSnapshot to bail out, then it would have
      // incorrectly bailed out here instead of re-rendering.
      'B2',
    ]);
    expect(container.textContent).toEqual('B2');
  });
  it('mutating the store in between render and commit when getSnapshot has _not_ changed', async () => {
    // Same as previous test, but `getSnapshot` does not change
    const store = createExternalStore({
      a: 1,
      b: 1,
    });
    const getSnapshotA = () => store.getState().a;
    function Child1({step}) {
      const value = useSyncExternalStore(store.subscribe, store.getState);
      useLayoutEffect(() => {
        if (step === 1) {
          // Update B in a layout effect. This happens in the same commit
          // that changed the getSnapshot in Child2. Child2's effects haven't
          // fired yet, so it doesn't have access to the latest getSnapshot. So
          // it can't use the getSnapshot to bail out.
          Scheduler.log('Update B in commit phase');
          store.set({
            a: value.a,
            b: 2,
          });
        }
      }, [step]);
      return null;
    }
    function Child2({step}) {
      const value = useSyncExternalStore(store.subscribe, getSnapshotA);
      return React.createElement(Text, {
        text: 'A' + value,
      });
    }
    let setStep;
    function App() {
      const [step, _setStep] = useState(0);
      setStep = _setStep;
      return React.createElement(
        React.Fragment,
        null,
        React.createElement(Child1, {
          step: step,
        }),
        React.createElement(Child2, {
          step: step,
        }),
      );
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog(['A1']);
    expect(container.textContent).toEqual('A1');

    // This will cause a layout effect, and in the layout effect we'll update
    // the store
    await act(() => {
      setStep(1);
    });
    assertLog([
      'A1',
      // This updates B, but since Child2 doesn't subscribe to B, it doesn't
      // need to re-render.
      'Update B in commit phase',
      // No re-render
    ]);
    expect(container.textContent).toEqual('A1');
  });
  it("does not bail out if the previous update hasn't finished yet", async () => {
    const store = createExternalStore(0);
    function Child1() {
      const value = useSyncExternalStore(store.subscribe, store.getState);
      useLayoutEffect(() => {
        if (value === 1) {
          Scheduler.log('Reset back to 0');
          store.set(0);
        }
      }, [value]);
      return React.createElement(Text, {
        text: value,
      });
    }
    function Child2() {
      const value = useSyncExternalStore(store.subscribe, store.getState);
      return React.createElement(Text, {
        text: value,
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() =>
      root.render(
        React.createElement(
          React.Fragment,
          null,
          React.createElement(Child1, null),
          React.createElement(Child2, null),
        ),
      ),
    );
    assertLog([0, 0]);
    expect(container.textContent).toEqual('00');
    await act(() => {
      store.set(1);
    });
    assertLog([1, 1, 'Reset back to 0', 0, 0]);
    expect(container.textContent).toEqual('00');
  });
  it('uses the latest getSnapshot, even if it changed in the same batch as a store update', async () => {
    const store = createExternalStore({
      a: 0,
      b: 0,
    });
    const getSnapshotA = () => store.getState().a;
    const getSnapshotB = () => store.getState().b;
    let setGetSnapshot;
    function App() {
      const [getSnapshot, _setGetSnapshot] = useState(() => getSnapshotA);
      setGetSnapshot = _setGetSnapshot;
      const text = useSyncExternalStore(store.subscribe, getSnapshot);
      return React.createElement(Text, {
        text: text,
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog([0]);

    // Update the store and getSnapshot at the same time
    await act(() => {
      ReactDOM.flushSync(() => {
        setGetSnapshot(() => getSnapshotB);
        store.set({
          a: 1,
          b: 2,
        });
      });
    });
    // It should read from B instead of A
    assertLog([2]);
    expect(container.textContent).toEqual('2');
  });
  it('handles errors thrown by getSnapshot', async () => {
    class ErrorBoundary extends React.Component {
      state = {
        error: null,
      };
      static getDerivedStateFromError(error) {
        return {
          error,
        };
      }
      render() {
        if (this.state.error) {
          return React.createElement(Text, {
            text: this.state.error.message,
          });
        }
        return this.props.children;
      }
    }
    const store = createExternalStore({
      value: 0,
      throwInGetSnapshot: false,
      throwInIsEqual: false,
    });
    function App() {
      const {value} = useSyncExternalStore(store.subscribe, () => {
        const state = store.getState();
        if (state.throwInGetSnapshot) {
          throw new Error('Error in getSnapshot');
        }
        return state;
      });
      return React.createElement(Text, {
        text: value,
      });
    }
    const errorBoundary = React.createRef(null);
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() =>
      root.render(
        React.createElement(
          ErrorBoundary,
          {
            ref: errorBoundary,
          },
          React.createElement(App, null),
        ),
      ),
    );
    assertLog([0]);
    expect(container.textContent).toEqual('0');

    // Update that throws in a getSnapshot. We can catch it with an error boundary.
    if (__DEV__ && gate(flags => flags.enableUseSyncExternalStoreShim)) {
      // In 17, the error is re-thrown in DEV.
      await expect(async () => {
        await act(() => {
          store.set({
            value: 1,
            throwInGetSnapshot: true,
            throwInIsEqual: false,
          });
        });
      }).rejects.toThrow('Error in getSnapshot');
    } else {
      await act(() => {
        store.set({
          value: 1,
          throwInGetSnapshot: true,
          throwInIsEqual: false,
        });
      });
    }
    assertLog(
      gate(flags => flags.enableUseSyncExternalStoreShim)
        ? ['Error in getSnapshot']
        : [
            'Error in getSnapshot',
            // In a concurrent root, React renders a second time to attempt to
            // recover from the error.
            'Error in getSnapshot',
          ],
    );
    expect(container.textContent).toEqual('Error in getSnapshot');
  });
  it('Infinite loop if getSnapshot keeps returning new reference', async () => {
    const store = createExternalStore({});
    function App() {
      const text = useSyncExternalStore(store.subscribe, () => ({}));
      return React.createElement(Text, {
        text: JSON.stringify(text),
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await expect(async () => {
      await expect(async () => {
        await act(() => {
          ReactDOM.flushSync(async () =>
            root.render(React.createElement(App, null)),
          );
        });
      }).rejects.toThrow(
        'Maximum update depth exceeded. This can happen when a component repeatedly ' +
          'calls setState inside componentWillUpdate or componentDidUpdate. React limits ' +
          'the number of nested updates to prevent infinite loops.',
      );
    }).toErrorDev(
      gate(flags => flags.enableUseSyncExternalStoreShim)
        ? [
            'Maximum update depth exceeded. ',
            'The result of getSnapshot should be cached to avoid an infinite loop',
            'The above error occurred in the',
          ]
        : [
            'The result of getSnapshot should be cached to avoid an infinite loop',
          ],
      {
        withoutStack: gate(flags => {
          if (flags.enableUseSyncExternalStoreShim) {
            // Stacks don't work when mixing the source and the npm package.
            return flags.source ? 1 : 0;
          }
          return false;
        }),
      },
    );
  });
  it('getSnapshot can return NaN without infinite loop warning', async () => {
    const store = createExternalStore('not a number');
    function App() {
      const value = useSyncExternalStore(store.subscribe, () =>
        parseInt(store.getState(), 10),
      );
      return React.createElement(Text, {
        text: value,
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);

    // Initial render that reads a snapshot of NaN. This is OK because we use
    // Object.is algorithm to compare values.
    await act(() => root.render(React.createElement(App, null)));
    expect(container.textContent).toEqual('NaN');
    assertLog([NaN]);

    // Update to real number
    await act(() => store.set(123));
    expect(container.textContent).toEqual('123');
    assertLog([123]);

    // Update back to NaN
    await act(() => store.set('not a number'));
    expect(container.textContent).toEqual('NaN');
    assertLog([NaN]);
  });
  describe('extra features implemented in user-space', () => {
    it('memoized selectors are only called once per update', async () => {
      const store = createExternalStore({
        a: 0,
        b: 0,
      });
      function selector(state) {
        Scheduler.log('Selector');
        return state.a;
      }
      function App() {
        Scheduler.log('App');
        const a = useSyncExternalStoreWithSelector(
          store.subscribe,
          store.getState,
          null,
          selector,
        );
        return React.createElement(Text, {
          text: 'A' + a,
        });
      }
      const container = document.createElement('div');
      const root = createRoot(container);
      await act(() => root.render(React.createElement(App, null)));
      assertLog(['App', 'Selector', 'A0']);
      expect(container.textContent).toEqual('A0');

      // Update the store
      await act(() => {
        store.set({
          a: 1,
          b: 0,
        });
      });
      assertLog([
        // The selector runs before React starts rendering
        'Selector',
        'App',
        // And because the selector didn't change during render, we can reuse
        // the previous result without running the selector again
        'A1',
      ]);
      expect(container.textContent).toEqual('A1');
    });
    it('Using isEqual to bailout', async () => {
      const store = createExternalStore({
        a: 0,
        b: 0,
      });
      function A() {
        const {a} = useSyncExternalStoreWithSelector(
          store.subscribe,
          store.getState,
          null,
          state => ({
            a: state.a,
          }),
          (state1, state2) => state1.a === state2.a,
        );
        return React.createElement(Text, {
          text: 'A' + a,
        });
      }
      function B() {
        const {b} = useSyncExternalStoreWithSelector(
          store.subscribe,
          store.getState,
          null,
          state => {
            return {
              b: state.b,
            };
          },
          (state1, state2) => state1.b === state2.b,
        );
        return React.createElement(Text, {
          text: 'B' + b,
        });
      }
      function App() {
        return React.createElement(
          React.Fragment,
          null,
          React.createElement(A, null),
          React.createElement(B, null),
        );
      }
      const container = document.createElement('div');
      const root = createRoot(container);
      await act(() => root.render(React.createElement(App, null)));
      assertLog(['A0', 'B0']);
      expect(container.textContent).toEqual('A0B0');

      // Update b but not a
      await act(() => {
        store.set({
          a: 0,
          b: 1,
        });
      });
      // Only b re-renders
      assertLog(['B1']);
      expect(container.textContent).toEqual('A0B1');

      // Update a but not b
      await act(() => {
        store.set({
          a: 1,
          b: 1,
        });
      });
      // Only a re-renders
      assertLog(['A1']);
      expect(container.textContent).toEqual('A1B1');
    });
    it('basic server hydration', async () => {
      const store = createExternalStore('client');
      const ref = React.createRef();
      function App() {
        const text = useSyncExternalStore(
          store.subscribe,
          store.getState,
          () => 'server',
        );
        useEffect(() => {
          Scheduler.log('Passive effect: ' + text);
        }, [text]);
        return React.createElement(
          'div',
          {
            ref: ref,
          },
          React.createElement(Text, {
            text: text,
          }),
        );
      }
      const container = document.createElement('div');
      container.innerHTML = '<div>server</div>';
      const serverRenderedDiv = container.getElementsByTagName('div')[0];
      if (gate(flags => !flags.enableUseSyncExternalStoreShim)) {
        await act(() => {
          ReactDOMClient.hydrateRoot(container, React.createElement(App, null));
        });
        assertLog([
          // First it hydrates the server rendered HTML
          'server',
          'Passive effect: server',
          // Then in a second paint, it re-renders with the client state
          'client',
          'Passive effect: client',
        ]);
      } else {
        // In the userspace shim, there's no mechanism to detect whether we're
        // currently hydrating, so `getServerSnapshot` is not called on the
        // client. To avoid this server mismatch warning, user must account for
        // this themselves and return the correct value inside `getSnapshot`.
        await act(() => {
          expect(() =>
            ReactDOM.hydrate(React.createElement(App, null), container),
          ).toErrorDev('Text content did not match');
        });
        assertLog(['client', 'Passive effect: client']);
      }
      expect(container.textContent).toEqual('client');
      expect(ref.current).toEqual(serverRenderedDiv);
    });
  });
  it('regression test for #23150', async () => {
    const store = createExternalStore('Initial');
    function App() {
      const text = useSyncExternalStore(store.subscribe, store.getState);
      const [derivedText, setDerivedText] = useState(text);
      useEffect(() => {}, []);
      if (derivedText !== text.toUpperCase()) {
        setDerivedText(text.toUpperCase());
      }
      return React.createElement(Text, {
        text: derivedText,
      });
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => root.render(React.createElement(App, null)));
    assertLog(['INITIAL']);
    expect(container.textContent).toEqual('INITIAL');
    await act(() => {
      store.set('Updated');
    });
    assertLog(['UPDATED']);
    expect(container.textContent).toEqual('UPDATED');
  });
  it('compares selection to rendered selection even if selector changes', async () => {
    const store = createExternalStore({
      items: ['A', 'B'],
    });
    const shallowEqualArray = (a, b) => {
      if (a.length !== b.length) {
        return false;
      }
      for (let i = 0; i < a.length; i++) {
        if (a[i] !== b[i]) {
          return false;
        }
      }
      return true;
    };
    const List = React.memo(({items}) => {
      return React.createElement(
        'ul',
        null,
        items.map(text =>
          React.createElement(
            'li',
            {
              key: text,
            },
            React.createElement(Text, {
              key: text,
              text: text,
            }),
          ),
        ),
      );
    });
    function App({step}) {
      const inlineSelector = state => {
        Scheduler.log('Inline selector');
        return [...state.items, 'C'];
      };
      const items = useSyncExternalStoreWithSelector(
        store.subscribe,
        store.getState,
        null,
        inlineSelector,
        shallowEqualArray,
      );
      return React.createElement(
        React.Fragment,
        null,
        React.createElement(List, {
          items: items,
        }),
        React.createElement(Text, {
          text: 'Sibling: ' + step,
        }),
      );
    }
    const container = document.createElement('div');
    const root = createRoot(container);
    await act(() => {
      root.render(
        React.createElement(App, {
          step: 0,
        }),
      );
    });
    assertLog(['Inline selector', 'A', 'B', 'C', 'Sibling: 0']);
    await act(() => {
      root.render(
        React.createElement(App, {
          step: 1,
        }),
      );
    });
    assertLog([
      // We had to call the selector again because it's not memoized
      'Inline selector',
      // But because the result was the same (according to isEqual) we can
      // bail out of rendering the memoized list. These are skipped:
      // 'A',
      // 'B',
      // 'C',

      'Sibling: 1',
    ]);
  });
  describe('selector and isEqual error handling in extra', () => {
    let ErrorBoundary;
    beforeEach(() => {
      ErrorBoundary = class extends React.Component {
        state = {
          error: null,
        };
        static getDerivedStateFromError(error) {
          return {
            error,
          };
        }
        render() {
          if (this.state.error) {
            return React.createElement(Text, {
              text: this.state.error.message,
            });
          }
          return this.props.children;
        }
      };
    });
    it('selector can throw on update', async () => {
      const store = createExternalStore({
        a: 'a',
      });
      const selector = state => {
        if (typeof state.a !== 'string') {
          throw new TypeError('Malformed state');
        }
        return state.a.toUpperCase();
      };
      function App() {
        const a = useSyncExternalStoreWithSelector(
          store.subscribe,
          store.getState,
          null,
          selector,
        );
        return React.createElement(Text, {
          text: a,
        });
      }
      const container = document.createElement('div');
      const root = createRoot(container);
      await act(() =>
        root.render(
          React.createElement(
            ErrorBoundary,
            null,
            React.createElement(App, null),
          ),
        ),
      );
      assertLog(['A']);
      expect(container.textContent).toEqual('A');
      if (__DEV__ && gate(flags => flags.enableUseSyncExternalStoreShim)) {
        // In 17, the error is re-thrown in DEV.
        await expect(async () => {
          await act(() => {
            store.set({});
          });
        }).rejects.toThrow('Malformed state');
      } else {
        await act(() => {
          store.set({});
        });
      }
      expect(container.textContent).toEqual('Malformed state');
    });
    it('isEqual can throw on update', async () => {
      const store = createExternalStore({
        a: 'A',
      });
      const selector = state => state.a;
      const isEqual = (left, right) => {
        if (typeof left.a !== 'string' || typeof right.a !== 'string') {
          throw new TypeError('Malformed state');
        }
        return left.a.trim() === right.a.trim();
      };
      function App() {
        const a = useSyncExternalStoreWithSelector(
          store.subscribe,
          store.getState,
          null,
          selector,
          isEqual,
        );
        return React.createElement(Text, {
          text: a,
        });
      }
      const container = document.createElement('div');
      const root = createRoot(container);
      await act(() =>
        root.render(
          React.createElement(
            ErrorBoundary,
            null,
            React.createElement(App, null),
          ),
        ),
      );
      assertLog(['A']);
      expect(container.textContent).toEqual('A');
      if (__DEV__ && gate(flags => flags.enableUseSyncExternalStoreShim)) {
        // In 17, the error is re-thrown in DEV.
        await expect(async () => {
          await act(() => {
            store.set({});
          });
        }).rejects.toThrow('Malformed state');
      } else {
        await act(() => {
          store.set({});
        });
      }
      expect(container.textContent).toEqual('Malformed state');
    });
  });
});