深入了解最新功能和改進

React 19：深入探討最新功能和改進

介紹

React 19 為流行的前端庫帶來了多項突破性的功能和改進。在這份綜合指南中，我們將探討主要變更以及它們如何增強您的 React 應用程式。

1. 行動和使用樂觀狀態

行動

操作提供了一種處理表單提交和資料突變的新方法：

import { useAction } from 'react';

function TodoForm() {
  const addTodo = useAction(async (formData: FormData) => {
    const title = formData.get('title');
    await saveTodoToDatabase({ title });
  });

  return (
    

Add Todo

); }

樂觀的更新

新的樂觀狀態功能可以透過即時回饋提供更好的使用者體驗：

import { useOptimistic, useAction } from 'react';

function TodoList() {
  const [todos, setTodos] = useState([]);
  const [optimisticTodos, addOptimisticTodo] = useOptimistic(
    todos,
    (state, newTodo) => [...state, newTodo]
  );

  const addTodo = useAction(async (formData: FormData) => {
    const title = formData.get('title');
    const newTodo = { id: Date.now(), title };

    addOptimisticTodo(newTodo);
    await saveTodoToDatabase(newTodo);
  });

  return (
    <div>
      <form action="%7BaddTodo%7D">
        <input name="title">
        <button type="submit">Add</button>
      </form>
      <ul>
        {optimisticTodos.map(todo => (
          <li key="{todo.id}">{todo.title}</li>
        ))}
      </ul>
    </div>
  );
}

2. 文檔元數據

新元標籤 API

React 19 引進了一種管理文件元資料的新方法：

import { Meta, Title } from 'react-meta';

function BlogPost({ post }) {
  return (
    
      <title>{post.title} | My Blog</title>
      <meta name="description" content="{post.excerpt}">
      <meta property="og:title" content="{post.title}">
      <meta property="og:description" content="{post.excerpt}">

      <article>
        <h1>{post.title}</h1>
        <p>{post.content}</p>
      </article>
    >
  );
}

3. 增強的伺服器元件

充滿懸念的直播

透過更好的 Suspense 整合改進了串流功能：

import { Suspense } from 'react';

function AsyncUserProfile({ userId }) {
  return (
    <suspense fallback="{<LoadingSpinner"></suspense>}>
      <userdata userid="{userId}"></userdata>
      <suspense fallback="{<PostsPlaceholder"></suspense>}>
        <userposts userid="{userId}"></userposts>
      
      <suspense fallback="{<ActivityPlaceholder"></suspense>}>
        <useractivity userid="{userId}"></useractivity>
      
    
  );
}

async function UserData({ userId }) {
  const user = await fetchUser(userId);
  return (
    <div classname="profile">
      <h2>{user.name}</h2>
      <p>{user.bio}</p>
    </div>
  );
}

4. 資源加載優化

資源預先載入

用於最佳化資源載入的新 API：

import { preloadImage, preloadFont } from 'react';

function App() {
  // Preload critical images
  preloadImage('/hero-image.jpg');

  // Preload fonts
  preloadFont('/fonts/OpenSans-Regular.woff2', {
    as: 'font',
    type: 'font/woff2',
    crossOrigin: 'anonymous',
  });

  return (
    <div>
      <img src="/hero-image.jpg" alt="深入了解最新功能和改進">
      <p classname="open-sans">Welcome to our site!</p>
    </div>
  );
}

5. 增強的鉤子

useFormState 鉤子

用於管理表單狀態的新掛鉤：

import { useFormState } from 'react';

function LoginForm() {
  const [state, formAction] = useFormState(async (prevState, formData) => {
    const email = formData.get('email');
    const password = formData.get('password');

    try {
      await loginUser(email, password);
      return { success: true };
    } catch (error) {
      return { error: error.message };
    }
  }, { error: null, success: false });

  return (
    

{state.error &&

{state.error}

} {state.success &&

Login successful!

} Login

); }

useTransition 改進

增強的過渡管理：

import { useTransition, startTransition } from 'react';

function TabPanel({ tabs }) {
  const [isPending, startTransition] = useTransition();
  const [activeTab, setActiveTab] = useState(0);

  const changeTab = (index) => {
    startTransition(() => {
      setActiveTab(index);
    });
  };

  return (
    <div>
      <div classname="tabs">
        {tabs.map((tab, index) => (
          <button key="{index}" onclick="{()"> changeTab(index)}
            className={activeTab === index ? 'active' : ''}
          >
            {tab.label}
          </button>
        ))}
      </div>

      <div classname="content">
        {isPending ? (
          <loadingspinner></loadingspinner>
        ) : (
          <tabcontent data="{tabs[activeTab].content}"></tabcontent>
        )}
      </div>
    </div>
  );
}

6. 性能改進

自動配料

增強狀態更新的自動批次：

function UserDashboard() {
  const [profile, setProfile] = useState(null);
  const [posts, setPosts] = useState([]);
  const [notifications, setNotifications] = useState([]);

  const refreshData = async () => {
    // React 19 automatically batches these updates
    // even in async functions
    setProfile(await fetchProfile());
    setPosts(await fetchPosts());
    setNotifications(await fetchNotifications());
  };

  return (
    <div>
      <profile data="{profile}"></profile>
      <posts data="{posts}"></posts>
      <notifications data="{notifications}"></notifications>
    </div>
  );
}

7. 錯誤處理

增強的誤差邊界

改進的錯誤邊界功能：

import { Component, ErrorBoundary } from 'react';

function ErrorFallback({ error, resetError }) {
  return (
    <div classname="error-container">
      <h2>Something went wrong</h2>
      <pre class="brush:php;toolbar:false">{error.message}

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