React 19 稳定版 All In One

React 19 稳定版 All In One

React 19 新功能

Actions

In React 19, we’re adding support for using async functions in transitions to handle pending states, errors, forms, and optimistic updates automatically.

useTransition

// Using pending state from Actions
function UpdateName({}) {
  const [name, setName] = useState("");
  const [error, setError] = useState(null);
  const [isPending, startTransition] = useTransition();

  const handleSubmit = () => {
    startTransition(async () => {
      const error = await updateName(name);
      if (error) {
        setError(error);
        return;
      } 
      redirect("/path");
    })
  };

  return (
    <div>
      <input value={name} onChange={(event) => setName(event.target.value)} />
      <button onClick={handleSubmit} disabled={isPending}>
        Update
      </button>
      {error && <p>{error}</p>}
    </div>
  );
}

old version useState

// Before Actions
function UpdateName({}) {
  const [name, setName] = useState("");
  const [error, setError] = useState(null);
  const [isPending, setIsPending] = useState(false);

  const handleSubmit = async () => {
    setIsPending(true);
    const error = await updateName(name);
    setIsPending(false);
    if (error) {
      setError(error);
      return;
    } 
    redirect("/path");
  };

  return (
    <div>
      <input value={name} onChange={(event) => setName(event.target.value)} />
      <button onClick={handleSubmit} disabled={isPending}>
        Update
      </button>
      {error && <p>{error}</p>}
    </div>
  );
}

New hook: useActionState

const [error, submitAction, isPending] = useActionState(
  async (previousState, newName) => {
    const error = await updateName(newName);
    if (error) {
      // You can return any result of the action.
      // Here, we return only the error.
      return error;
    }

    // handle success
    return null;
  },
  null,
);

https://react.dev/reference/react/useActionState

https://react.dev/blog/2024/12/05/react-19#new-hook-useactionstate

React DOM: <form> Actions

<form action={actionFunction}>

https://react.dev/reference/react-dom/components/form
https://react.dev/reference/react-dom/components/input

React DOM: New hook: useFormStatus

import {useFormStatus} from 'react-dom';

function DesignButton() {
  const {pending} = useFormStatus();
  return <button type="submit" disabled={pending} />
}

https://react.dev/reference/react-dom/hooks/useFormStatus

New hook: useOptimistic

function ChangeName({currentName, onUpdateName}) {
  const [optimisticName, setOptimisticName] = useOptimistic(currentName);

  const submitAction = async formData => {
    const newName = formData.get("name");
    setOptimisticName(newName);
    const updatedName = await updateName(newName);
    onUpdateName(updatedName);
  };

  return (
    <form action={submitAction}>
      <p>Your name is: {optimisticName}</p>
      <p>
        <label>Change Name:</label>
        <input
          type="text"
          name="name"
          disabled={currentName !== optimisticName}
        />
      </p>
    </form>
  );
}

https://react.dev/reference/react/useOptimistic

New API: use

import {use} from 'react';

function Comments({commentsPromise}) {
  // `use` will suspend until the promise resolves.
  const comments = use(commentsPromise);
  return comments.map(comment => <p key={comment.id}>{comment}</p>);
}

function Page({commentsPromise}) {
  // When `use` suspends in Comments,
  // this Suspense boundary will be shown.
  return (
    <Suspense fallback={<div>Loading...</div>}>
      <Comments commentsPromise={commentsPromise} />
    </Suspense>
  )
}

use does not support promises created in render.

❌ A component was suspended by an uncached promise. Creating promises inside a Client Component or hook is not yet supported, except via a Suspense-compatible library or framework.

import {use} from 'react';
import ThemeContext from './ThemeContext'

function Heading({children}) {
  if (children == null) {
    return null;
  }
  
  // This would not work with useContext
  // because of the early return.
  const theme = use(ThemeContext);
  return (
    <h1 style={{color: theme.color}}>
      {children}
    </h1>
  );
}

New React DOM Static APIs

https://react.dev/reference/react-dom/static

prerender

import { prerender } from 'react-dom/static';

async function handler(request) {
  const {prelude} = await prerender(<App />, {
    bootstrapScripts: ['/main.js']
  });
  return new Response(prelude, {
    headers: { 'content-type': 'text/html' },
  });
}

https://react.dev/reference/react-dom/static/prerender

prerenderToNodeStream

https://react.dev/reference/react-dom/static/prerenderToNodeStream

React Server Components

https://react.dev/reference/react-dom/server

https://react.dev/learn/start-a-new-react-project#which-features-make-up-the-react-teams-full-stack-architecture-vision

Server Components

https://react.dev/reference/rsc/server-components

Server Actions

https://react.dev/reference/rsc/server-actions

React 19 中的改进

ref as a prop

function MyInput({placeholder, ref}) {
  return <input placeholder={placeholder} ref={ref} />
}

//...
<MyInput ref={ref} />

Diffs for hydration errors

<Context> as a provider

In React 19, you can render <Context> as a provider instead of <Context.Provider>:

const ThemeContext = createContext('');

function App({children}) {
  return (
    <ThemeContext value="dark">
      {children}
    </ThemeContext>
  );  
}

Cleanup functions for refs

<input
  ref={(ref) => {
    // ref created

    // NEW: return a cleanup function to reset the ref when element is removed from DOM.
    return () => {
      // ref cleanup
    };
  }}
/>

TypeScript

- <div ref={current => (instance = current)} />
+ <div ref={current => {instance = current}} />

https://github.com/eps1lon/types-react-codemod/#no-implicit-ref-callback-return

useDeferredValue initial value

function Search({deferredValue}) {
  // On initial render the value is ''.
  // Then a re-render is scheduled with the deferredValue.
  const value = useDeferredValue(deferredValue, '');
  
  return (
    <Results query={value} />
  );
}

https://react.dev/reference/react/useDeferredValue

Support for Document Metadata

In React 19, we’re adding support for rendering document metadata tags in components natively:

function BlogPost({post}) {
  return (
    <article>
      <h1>{post.title}</h1>
      <title>{post.title}</title>
      <meta name="author" content="Josh" />
      <link rel="author" href="https://twitter.com/joshcstory/" />
      <meta name="keywords" content={post.keywords} />
      <p>
        Eee equals em-see-squared...
      </p>
    </article>
  );
}

https://react.dev/reference/react-dom/components/meta

https://react.dev/reference/react-dom/components/title

https://react.dev/reference/react-dom/components/link

Support for stylesheets

function ComponentOne() {
  return (
    <Suspense fallback="loading...">
      <link rel="stylesheet" href="foo" precedence="default" />
      <link rel="stylesheet" href="bar" precedence="high" />
      <article class="foo-class bar-class">
        {...}
      </article>
    </Suspense>
  )
}

function ComponentTwo() {
  return (
    <div>
      <p>{...}</p>
      <link rel="stylesheet" href="baz" precedence="default" />  <-- will be inserted between foo & bar
    </div>
  )
}

function App() {
  return <>
    <ComponentOne />
    ...
    <ComponentOne /> // won't lead to a duplicate stylesheet link in the DOM
  </>
}

https://react.dev/reference/react-dom/components/style

Support for async scripts

function MyComponent() {
  return (
    <div>
      <script async={true} src="..." />
      Hello World
    </div>
  )
}

function App() {
  <html>
    <body>
      <MyComponent>
      ...
      <MyComponent> // won't lead to duplicate script in the DOM
    </body>
  </html>
}

https://react.dev/reference/react-dom/components/script

Support for preloading resources

import { prefetchDNS, preconnect, preload, preinit } from 'react-dom'
function MyComponent() {
  preinit('https://.../path/to/some/script.js', {as: 'script' }) // loads and executes this script eagerly
  preload('https://.../path/to/font.woff', { as: 'font' }) // preloads this font
  preload('https://.../path/to/stylesheet.css', { as: 'style' }) // preloads this stylesheet
  prefetchDNS('https://...') // when you may not actually request anything from this host
  preconnect('https://...') // when you will request something but aren't sure what
}

<!-- the above would result in the following DOM/HTML -->
<html>
  <head>
    <!-- links/scripts are prioritized by their utility to early loading, not call order -->
    <link rel="prefetch-dns" href="https://...">
    <link rel="preconnect" href="https://...">
    <link rel="preload" as="font" href="https://.../path/to/font.woff">
    <link rel="preload" as="style" href="https://.../path/to/stylesheet.css">
    <script async="" src="https://.../path/to/some/script.js"></script>
  </head>
  <body>
    ...
  </body>
</html>

https://react.dev/reference/react-dom#resource-preloading-apis

Compatibility with third-party scripts and extensions

Better error reporting

https://react.dev/reference/react-dom/client/createRoot

https://react.dev/reference/react-dom/client/hydrateRoot

Support for Custom Elements

https://custom-elements-everywhere.com/

demos

React 19 Upgrade Guide

https://react.dev/blog/2024/04/25/react-19-upgrade-guide

refs

https://react.dev/blog/2024/12/05/react-19

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