| 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 * as React from 'react'; |
| 11 | |
| 12 | const {useState, useEffect, useSyncExternalStore} = React; |
| 13 | |
| 14 | // Create a simple external store for demonstratio |
| 15 | function createStore<T>(initialValue: T): { |
| 16 | subscribe: (cb: () => void) => () => any, |
| 17 | getSnapshot: () => T, |
| 18 | setValue: (newValue: T) => void, |
| 19 | } { |
| 20 | let value = initialValue; |
| 21 | const subscribers = new Set<() => void>(); |
| 22 | |
| 23 | return { |
| 24 | subscribe(callback) { |
| 25 | subscribers.add(callback); |
| 26 | return () => subscribers.delete(callback); |
| 27 | }, |
| 28 | getSnapshot() { |
| 29 | return value; |
| 30 | }, |
| 31 | setValue(newValue) { |
| 32 | value = newValue; |
| 33 | subscribers.forEach(callback => callback()); |
| 34 | }, |
| 35 | }; |
| 36 | } |
| 37 | |
| 38 | const counterStore = createStore(0); |
| 39 | const themeStore = createStore('light'); |
| 40 | |
| 41 | export default function UseSyncExternalStore(): React.Node { |
| 42 | return ( |
| 43 | <> |
| 44 | <h2>useSyncExternalStore()</h2> |
| 45 | <SingleHookCase /> |
| 46 | <HookTreeCase /> |
| 47 | <MultipleStoresCase /> |
| 48 | </> |
| 49 | ); |
| 50 | } |
| 51 | |
| 52 | function SingleHookCase(): React.Node { |
| 53 | const count = useSyncExternalStore( |
| 54 | counterStore.subscribe, |
| 55 | counterStore.getSnapshot, |
| 56 | ); |
| 57 | |
| 58 | return ( |
| 59 | <div> |
| 60 | <h3>Single hook case</h3> |
| 61 | <p>Count: {count}</p> |
| 62 | <button onClick={() => counterStore.setValue(count + 1)}> |
| 63 | Increment |
| 64 | </button> |
| 65 | <button onClick={() => counterStore.setValue(count - 1)}> |
| 66 | Decrement |
| 67 | </button> |
| 68 | </div> |
| 69 | ); |
| 70 | } |
| 71 | |
| 72 | function useCounter() { |
| 73 | const count = useSyncExternalStore( |
| 74 | counterStore.subscribe, |
| 75 | counterStore.getSnapshot, |
| 76 | ); |
| 77 | const [localState, setLocalState] = useState(0); |
| 78 | |
| 79 | useEffect(() => { |
| 80 | // Some effect |
| 81 | }, [count]); |
| 82 | |
| 83 | return {count, localState, setLocalState}; |
| 84 | } |
| 85 | |
| 86 | function HookTreeCase(): React.Node { |
| 87 | const {count, localState, setLocalState} = useCounter(); |
| 88 | |
| 89 | return ( |
| 90 | <div> |
| 91 | <h3>Hook tree case</h3> |
| 92 | <p>External count: {count}</p> |
| 93 | <p>Local state: {localState}</p> |
| 94 | <button onClick={() => counterStore.setValue(count + 1)}> |
| 95 | Increment External |
| 96 | </button> |
| 97 | <button onClick={() => setLocalState(localState + 1)}> |
| 98 | Increment Local |
| 99 | </button> |
| 100 | </div> |
| 101 | ); |
| 102 | } |
| 103 | |
| 104 | function useTheme() { |
| 105 | const theme = useSyncExternalStore( |
| 106 | themeStore.subscribe, |
| 107 | themeStore.getSnapshot, |
| 108 | ); |
| 109 | |
| 110 | return theme; |
| 111 | } |
| 112 | |
| 113 | function MultipleStoresCase() { |
| 114 | const count = useSyncExternalStore( |
| 115 | counterStore.subscribe, |
| 116 | counterStore.getSnapshot, |
| 117 | ); |
| 118 | const theme = useTheme(); |
| 119 | |
| 120 | return ( |
| 121 | <div style={{background: theme === 'dark' ? '#333' : '#fff'}}> |
| 122 | <h3>Multiple stores case</h3> |
| 123 | <p>Count: {count}</p> |
| 124 | <p>Theme: {theme}</p> |
| 125 | <button |
| 126 | onClick={() => |
| 127 | themeStore.setValue(theme === 'light' ? 'dark' : 'light') |
| 128 | }> |
| 129 | Toggle Theme |
| 130 | </button> |
| 131 | </div> |
| 132 | ); |
| 133 | } |