深入了解最新功能和改进

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react 19：深入探讨最新功能和改进

介绍

react 19 为流行的前端库带来了多项突破性的功能和改进。在这份综合指南中，我们将探讨主要变化以及它们如何增强您的 react 应用程序。

1. 行动和使用乐观状态

行动

操作提供了一种处理表单提交和数据突变的新方法：

import { useaction } from 'react';

function todoform() {
  const addtodo = useaction(async (formdata: formdata) => {
    const title = formdata.get('title');
    await savetodotodatabase({ title });
  });

  return (
    <form action={addtodo}>
      &lt;input name=&quot;title&quot; type=&quot;text&quot; /&gt;
      <button type="submit">add todo</button>
    </form>
  );
}

乐观的更新

新的乐观状态功能可以通过即时反馈提供更好的用户体验：

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={addtodo}>
        &lt;input name=&quot;title&quot; /&gt;
        <button type="submit">add</button>
      </form>
      <ul>
        {optimistictodos.map(todo => (
          <li key={todo.id}>{todo.title}</li>
        ))}
      </ul>
    </div>
  );
}

2. 文档元数据

新元标签 api

react 19 引入了一种管理文档元数据的新方法：

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. 增强的服务器组件

充满悬念的直播

通过更好的 suspense 集成改进了流媒体功能：

import { suspense } from 'react';

function asyncuserprofile({ userid }) {
  return (
    <suspense fallback={<loadingspinner />}>
      <userdata userid={userid} />
      <suspense fallback={<postsplaceholder />}>
        <userposts userid={userid} />
      </suspense>
      <suspense fallback={<activityplaceholder />}>
        <useractivity userid={userid} />
      </suspense>
    </suspense>
  );
}

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

4. 资源加载优化

资源预加载

用于优化资源加载的新 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="hero" />
      <p classname="open-sans">welcome to our site!</p>
    </div>
  );
}

5. 增强的钩子

useformstate 钩子

用于管理表单状态的新挂钩：

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 (
    <form action={formaction}>
      {state.error && <p classname="error">{state.error}</p>}
      {state.success && <p classname="success">login successful!</p>}

      &lt;input name=&quot;email&quot; type=&quot;email&quot; required /&gt;
      &lt;input name=&quot;password&quot; type=&quot;password&quot; required /&gt;
      <button type="submit">login</button>
    </form>
  );
}

usetransition 改进

增强的过渡管理：

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 />
        ) : (
          <tabcontent data={tabs[activetab].content} />
        )}
      </div>
    </div>
  );
}

6. 性能改进

自动配料

增强状态更新的自动批处理：

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} />
      <posts data={posts} />
      <notifications data={notifications} />
    </div>
  );
}

7. 错误处理

增强的误差边界

改进的错误边界功能：

import { Component, ErrorBoundary } from 'react';

function ErrorFallback({ error, resetError }) {
  return (
    <div className="error-container">
      <h2>Something went wrong</h2>
      <pre>{error.message}