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React 中hooks之useSyncExternalStore使用总结

news 2025/7/2 13:55:50

1. 基本概念

useSyncExternalStore 是 React 18 引入的一个 Hook，用于订阅外部数据源，确保在并发渲染下数据的一致性。它主要用于：

订阅浏览器 API（如 window.width）
订阅第三方状态管理库
订阅任何外部数据源

1.1 基本语法

const state = useSyncExternalStore(subscribe,  // 订阅函数getSnapshot, // 获取当前状态的函数getServerSnapshot // 可选：服务端渲染时获取状态的函数
);

2. 基础示例

2.1 订阅窗口大小变化

getSnapshot 是一个函数，用于返回当前浏览器窗口的宽度和高度。window.innerWidth 和 window.innerHeight 分别获取浏览器窗口的宽度和高度。
该函数返回一个对象，包含 width 和 height 两个属性。
subscribe 函数接受一个回调函数 callback，并将其作为事件监听器绑定到 resize 事件上。
每当浏览器窗口的尺寸发生变化时，resize 事件会触发，进而调用 callback。
subscribe 函数还返回一个清理函数（return () => window.removeEventListener(‘resize’, callback)），用于在组件卸载时移除事件监听器，防止内存泄漏。
当callback回调触发的时候就会触发组件更新

function useWindowSize() {const getSnapshot = () => ({width: window.innerWidth,height: window.innerHeight});const subscribe = (callback) => {window.addEventListener('resize', callback);return () => window.removeEventListener('resize', callback);};return useSyncExternalStore(subscribe, getSnapshot);
}function WindowSizeComponent() {const { width, height } = useWindowSize();return (<div>Window size: {width} x {height}</div>);
}

2.2 订阅浏览器在线状态

function useOnlineStatus() {const getSnapshot = () => navigator.onLine;const subscribe = (callback) => {window.addEventListener('online', callback);window.addEventListener('offline', callback);return () => {window.removeEventListener('online', callback);window.removeEventListener('offline', callback);};};return useSyncExternalStore(subscribe, getSnapshot);
}function OnlineStatusComponent() {const isOnline = useOnlineStatus();return (<div>Status: {isOnline ? '在线' : '离线'}</div>);
}

3. 进阶用法

3.1 创建自定义存储

useTodoStore 是一个自定义 Hook，它使用了 useSyncExternalStore 来同步外部存储（即 todoStore）的状态。
todoStore.subscribe：订阅状态更新。每当 todoStore 中的状态变化时，useSyncExternalStore 会触发重新渲染。
todoStore.getSnapshot：获取当前的状态快照，在此返回的对象包含 todos 和 filter。

function createStore(initialState) {let state = initialState;const listeners = new Set();return {subscribe(listener) {listeners.add(listener);return () => listeners.delete(listener);},getSnapshot() {return state;},setState(newState) {state = newState;listeners.forEach(listener => listener());}};
}const todoStore = createStore({todos: [],filter: 'all'
});function useTodoStore() {return useSyncExternalStore(todoStore.subscribe,todoStore.getSnapshot);
}function TodoList() {const { todos, filter } = useTodoStore();return (<ul>{todos.filter(todo => filter === 'all' || todo.completed === (filter === 'completed')).map(todo => (<li key={todo.id}>{todo.text}</li>))}</ul>);
}

3.2 与服务端渲染集成

function useSharedState(initialState) {const store = useMemo(() => createStore(initialState), [initialState]);// 提供服务端快照const getServerSnapshot = () => initialState;return useSyncExternalStore(store.subscribe,store.getSnapshot,getServerSnapshot);
}

3.3 订阅 WebSocket 数据

function useWebSocketData(url) {const [store] = useState(() => {let data = null;const listeners = new Set();const ws = new WebSocket(url);ws.onmessage = (event) => {data = JSON.parse(event.data);listeners.forEach(listener => listener());};return {subscribe(listener) {listeners.add(listener);return () => {listeners.delete(listener);if (listeners.size === 0) {ws.close();}};},getSnapshot() {return data;}};});return useSyncExternalStore(store.subscribe, store.getSnapshot);
}function LiveDataComponent() {const data = useWebSocketData('wss://api.example.com/live');if (!data) return <div>Loading...</div>;return (<div><h2>实时数据</h2><pre>{JSON.stringify(data, null, 2)}</pre></div>);
}

4. 性能优化

4.1 选择性订阅

function useStoreSelector(selector) {const store = useContext(StoreContext);const getSnapshot = useCallback(() => {return selector(store.getSnapshot());}, [store, selector]);return useSyncExternalStore(store.subscribe,getSnapshot);
}// 使用示例
function TodoCounter() {const count = useStoreSelector(state => state.todos.length);return <div>Total todos: {count}</div>;
}

4.2 避免不必要的更新

function createStoreWithSelector(initialState) {let state = initialState;const listeners = new Map();return {subscribe(listener, selector) {const wrappedListener = () => {const newSelectedValue = selector(state);if (newSelectedValue !== selector(previousState)) {listener();}};listeners.set(listener, wrappedListener);return () => listeners.delete(listener);},getSnapshot() {return state;},setState(newState) {const previousState = state;state = newState;listeners.forEach(listener => listener());}};
}

5. 实际应用场景

5.1 主题切换系统

function createThemeStore() {let theme = 'light';const listeners = new Set();return {subscribe(listener) {listeners.add(listener);return () => listeners.delete(listener);},getSnapshot() {return theme;},toggleTheme() {theme = theme === 'light' ? 'dark' : 'light';listeners.forEach(listener => listener());}};
}const themeStore = createThemeStore();function useTheme() {return useSyncExternalStore(themeStore.subscribe,themeStore.getSnapshot);
}function ThemeToggle() {const theme = useTheme();return (<button onClick={() => themeStore.toggleTheme()}>Current theme: {theme}</button>);
}

5.2 表单状态管理

function createFormStore(initialValues) {let values = initialValues;const listeners = new Set();return {subscribe(listener) {listeners.add(listener);return () => listeners.delete(listener);},getSnapshot() {return values;},updateField(field, value) {values = { ...values, [field]: value };listeners.forEach(listener => listener());},reset() {values = initialValues;listeners.forEach(listener => listener());}};
}function useForm(initialValues) {const [store] = useState(() => createFormStore(initialValues));return useSyncExternalStore(store.subscribe,store.getSnapshot);
}function Form() {const formData = useForm({ name: '', email: '' });return (<form><inputvalue={formData.name}onChange={e => formStore.updateField('name', e.target.value)}/><inputvalue={formData.email}onChange={e => formStore.updateField('email', e.target.value)}/></form>);
}