| 1 | /** |
| 2 | * Copyright (c) Meta Platforms, Inc. and affiliates. |
| 3 | * |
| 4 | * This source code is licensed under the MIT license found in the |
| 5 | * LICENSE file in the root directory of this source tree. |
| 6 | * |
| 7 | * @flow |
| 8 | */ |
| 9 | |
| 10 | import {useSyncExternalStore} from 'use-sync-external-store/shim'; |
| 11 | |
| 12 | // Hook used for safely managing subscriptions in concurrent mode. |
| 13 | // |
| 14 | // In order to avoid removing and re-adding subscriptions each time this hook is called, |
| 15 | // the parameters passed to this hook should be memoized in some way– |
| 16 | // either by wrapping the entire params object with useMemo() |
| 17 | // or by wrapping the individual callbacks with useCallback(). |
| 18 | export function useSubscription<Value>({ |
| 19 | // (Synchronously) returns the current value of our subscription. |
| 20 | getCurrentValue, |
| 21 | |
| 22 | // This function is passed an event handler to attach to the subscription. |
| 23 | // It should return an unsubscribe function that removes the handler. |
| 24 | subscribe, |
| 25 | }: { |
| 26 | getCurrentValue: () => Value, |
| 27 | subscribe: (callback: Function) => () => void, |
| 28 | }): Value { |
| 29 | return useSyncExternalStore(subscribe, getCurrentValue); |
| 30 | } |