React 19 features migration

React 19 Features Migration Guide: Complete Walkthrough

React 19 features migration guide covers everything you need to upgrade your applications from React 18. Therefore, understanding the new APIs like Actions, useOptimistic, and the React Compiler is essential for modern frontend development. In this guide, you will learn how to migrate incrementally without breaking your existing codebase.

React 19 Features Migration Guide: What Changed

React 19 introduces the most significant API changes since Hooks. As a result, moreover, the new React Compiler eliminates the need for manual memoization with useMemo, useCallback, and React.memo. Consequently, your code becomes simpler while performance improves automatically.

Additionally, Actions replace the pattern of managing pending states, errors, and optimistic updates manually. As a result, form handling and data mutations become dramatically simpler.

React 19 Features Migration Guide: Actions and useActionState

Actions are the headline feature of React 19. For this reason, specifically, they provide built-in handling for async transitions with pending states, error handling, and form support:

function UpdateProfile() {
  const [error, submitAction, isPending] = useActionState(
    async (prevState, formData) => {
      const result = await updateUser(formData);
      if (result.error) return result.error;
      redirect('/profile');
    },
    null
  );

  return (
    <form action={submitAction}>
      <input name="name" />
      <button disabled={isPending}>
        {isPending ? 'Saving...' : 'Save'}
      </button>
      {error && 
{error}
}
    </form>
  );
}

The use() Hook

The new use() hook reads resources like Promises and Context during render. Furthermore, it works with Suspense for async data fetching without useEffect:

function UserProfile({ userPromise }) {
  const user = use(userPromise); // Suspends until resolved
  return <h1>{user.name}</h1>;
}

Additionally, use() can read Context conditionally, which was impossible with useContext. As a result, you gain more flexibility in component composition.

React 19 Features Migration Guide: useOptimistic Hook

Optimistic UI updates make applications feel instant. On the other hand, moreover, React 19's useOptimistic hook provides a standardized pattern for this common requirement:

function TodoList({ todos }) {
  const [optimisticTodos, addOptimistic] = useOptimistic(
    todos,
    (state, newTodo) => [...state, { ...newTodo, pending: true }]
  );

  async function addTodo(formData) {
    const todo = { text: formData.get('text') };
    addOptimistic(todo);
    await saveTodo(todo);
  }
  return /* render optimisticTodos */;
}

React Compiler (React Forget)

The React Compiler automatically memoizes components and values. Therefore, you can remove most useMemo, useCallback, and React.memo calls from your codebase. Moreover, the compiler produces more granular memoization than manual approaches.

Migration Steps

–

Update to React 19: npm install react@19 react-dom@19

–

Run the codemod: npx @react-codemod/v19 ./src

–

Replace forwardRef with direct ref props

–

Migrate useEffect data fetching to use() + Suspense

–

Enable the React Compiler in your bundler config

For related frontend guides, see Next.js 15 Server Components and TypeScript 5.6 Features. In addition, additionally, the official React 19 blog post details every change.

Further Resources

For deeper understanding, check: MDN Web Docs, web.dev

React 19 New Features: Complete Migration Guide from React 18