# React 19 Deep Dive: What Changed and Why React 19 brings significant improvements to how we build applications. After upgrading several projects, I've compiled a comprehensive guide to the most impactful changes. --- ## New React Hooks ### `useActionState` Simplify form handling with the new `useActionState` hook: ```typescript import { useActionState } from 'react'; function LoginForm() { const [state, action, isPending] = useActionState(async (prev, form) => { const result = await login(form.get('username'), form.get('password')); return result; }, null); return ( ); } ``` ### `useFormStatus` Get form submission status without prop drilling: ```typescript import { useFormStatus } from 'react-dom'; function SubmitButton() { const { pending } = useFormStatus(); return ( ); } ``` --- ## Server Components Improvements ### Async Components Server components now support async operations naturally: ```typescript async function UserProfile({ userId }: { userId: string }) { const user = await db.query.users.findOne({ id: userId }); const posts = await db.query.posts.findMany({ userId }); return (

{user.name}

{post.title}

); } ``` --- ## Performance Enhancements ### Automatic Batching React 19 automatically batches all state updates, even in async operations: ```typescript function Counter() { const [count, setCount] = useState(0); const handleClick = async () => { // Both updates are batched into a single render setCount(c => c + 1); setCount(c => c + 1); await someAsyncOperation(); // These are also batched setCount(c => c + 1); setCount(c => c + 1); }; return ; } ``` --- ## Migration Path ### Step 1: Update Dependencies ```bash npm install react@19 react-dom@19 ``` ### Step 2: Update Type Definitions ```bash npm install --save-dev @types/react@19 @types/react-dom@19 ``` ### Step 3: Migrate Form Handling Replace form submission handlers with Server Actions and `useActionState`. --- ## Breaking Changes - **Automatic ref forwarding** is now the default - **Context as providers** syntax has changed slightly - **Some legacy APIs** have been deprecated --- ## Conclusion React 19 is a substantial upgrade that makes building complex applications easier and more efficient. The improvements to forms, server components, and performance are worth the migration effort. Have you upgraded to React 19 yet? Share your experience!

React 19 Deep Dive: What Changed and Why

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