What is new feature of React version19

Actions

A common use case in React apps is to perform a data mutation and then update state in response. For example, when a user submits a form to change their name, you will make an API request, and then handle the response. In the past, you would need to handle pending states, errors, optimistic updates, and sequential requests manually.

For example, you could handle the pending and error state in 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>
  );
}

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

For example, you can use useTransition to handle the pending state for you:

// 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>
  );
}

The async transition will immediately set the isPending state to true, make the async request(s), and switch isPending to false after any transitions. This allows you to keep the current UI responsive and interactive while the data is changing.

Note

By convention, functions that use async transitions are called “Actions”.
Actions automatically manage submitting data for you:

Pending state: Actions provide a pending state that starts at the beginning of a request and automatically resets when the final state update is committed.
Optimistic updates: Actions support the new useOptimistic hook so you can show users instant feedback while the requests are submitting.
Error handling: Actions provide error handling so you can display Error Boundaries when a request fails, and revert optimistic updates to their original value automatically.
Forms: <form> elements now support passing functions to the action and formAction props. Passing functions to the action props use Actions by default and reset the form automatically after submission.

Building on top of Actions, React 19 introduces useOptimistic to manage optimistic updates, and a new hook React.useActionState to handle common cases for Actions. In react-dom we’re adding <form> Actions to manage forms automatically and useFormStatus to support the common cases for Actions in forms.

In React 19, the above example can be simplified to:

// Using <form> Actions and useActionState
function ChangeName({ name, setName }) {
  const [error, submitAction, isPending] = useActionState(
    async (previousState, formData) => {
      const error = await updateName(formData.get("name"));
      if (error) {
        return error;
      }
      redirect("/path");
      return null;
    },
    null,
  );

  return (
    <form action={submitAction}>
      <input type="text" name="name" />
      <button type="submit" disabled={isPending}>Update</button>
      {error && <p>{error}</p>}
    </form>
  );
}

In the next section, we’ll break down each of the new Action features in React 19.

New hook: useActionState

To make the common cases easier for Actions, we’ve added a new hook called 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,
);

useActionState accepts a function (the “Action”), and returns a wrapped Action to call. This works because Actions compose. When the wrapped Action is called, useActionState will return the last result of the Action as data, and the pending state of the Action as pending.

Note

React.useActionState was previously called ReactDOM.useFormState in the Canary releases, but we’ve renamed it and deprecated useFormState.

See #28491 for more info.
For more information, see the docs for useActionState.

React DOM: <form> Actions

Actions are also integrated with React 19’s new <form> features for react-dom. We’ve added support for passing functions as the action and formAction props of <form>, <input>, and <button> elements to automatically submit forms with Actions:

<form action={actionFunction}>

When a <form> Action succeeds, React will automatically reset the form for uncontrolled components. If you need to reset the <form> manually, you can call the new requestFormReset React DOM API.

For more information, see the react-dom docs for <form>, <input>, and <button>.

React DOM: New hook: useFormStatus

In design systems, it’s common to write design components that need access to information about the <form> they’re in, without drilling props down to the component. This can be done via Context, but to make the common case easier, we’ve added a new hook useFormStatus:

import {useFormStatus} from 'react-dom';

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

useFormStatus reads the status of the parent <form> as if the form was a Context provider.

For more information, see the react-dom docs for useFormStatus.

New hook: useOptimistic

Another common UI pattern when performing a data mutation is to show the final state optimistically while the async request is underway. In React 19, we’re adding a new hook called useOptimistic to make this easier:

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>
  );
}

The useOptimistic hook will immediately render the optimisticName while the updateName request is in progress. When the update finishes or errors, React will automatically switch back to the currentName value.

For more information, see the docs for useOptimistic.

New API: use

In React 19 we’re introducing a new API to read resources in render: use.

For example, you can read a promise with use, and React will Suspend until the promise resolves:

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>
  )
}

Note

use does not support promises created in render.
If you try to pass a promise created in render to use, React will warn:

Error
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.

To fix, you need to pass a promise from a suspense powered library or framework that supports caching for promises. In the future we plan to ship features to make it easier to cache promises in render.

You can also read context with use, allowing you to read Context conditionally such as after early returns:

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>
  );
}

The use API can only be called in render, similar to hooks. Unlike hooks, use can be called conditionally. In the future we plan to support more ways to consume resources in render with use.

For more information, see the docs for use.

New React DOM Static APIs

We’ve added two new APIs to react-dom/static for static site generation:

• prerender
• prerenderToNodeStream

These new APIs improve on renderToString by waiting for data to load for static HTML generation. They are designed to work with streaming environments like Node.js Streams and Web Streams. For example, in a Web Stream environment, you can prerender a React tree to static HTML with 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' },
  });
}

Prerender APIs will wait for all data to load before returning the static HTML stream. Streams can be converted to strings, or sent with a streaming response. They do not support streaming content as it loads, which is

React Server Components

Server Components

Server Components are a new option that allows rendering components ahead of time, before bundling, in an environment separate from your client application or SSR server. This separate environment is the “server” in React Server Components. Server Components can run once at build time on your CI server, or they can be run for each request using a web server.

React 19 includes all of the React Server Components features included from the Canary channel. This means libraries that ship with Server Components can now target React 19 as a peer dependency with a react-server export condition for use in frameworks that support the Full-stack React Architecture.