packages/use-sync-external-store/src/useSyncExternalStoreShimServer.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

export function useSyncExternalStore<T>(
  subscribe: (() => void) => () => void,
  getSnapshot: () => T,
  getServerSnapshot?: () => T,
): T {
  // Note: The shim does not use getServerSnapshot, because pre-18 versions of
  // React do not expose a way to check if we're hydrating. So users of the shim
  // will need to track that themselves and return the correct value
  // from `getSnapshot`.
  return getSnapshot();
}