New Features in React 19

What's New in REACT 19?

1. REACT COMPILER

What New?

• React automatically optimizes rerenders without manual intervention.

• No more need for: useMemo(), useCallBack(), React.memo

Why React Compiler?

• Manual Optimization was tedious for developers.

• React now handles state changes and rerendering logic automatically.

Benefits

• React decides what to re-render and when.

• Reduces developer effort.

• cleaner, simpler codebase.

• currently powering instagram in production.

2. SERVER COMPONENTS

What New?

• components that run on the server not the client.

• Previously pioneered by Next.js (default in V13).

• In React 19, server components are integrated natively.

Benefits

• SEO Friendly: Enhances Search Engine Optimization.

• Performance Boost: Faster initial pages loads.

• Server Side Execution: Efficiently handles tasks like API calls.

How to use Server Components ?

1. Client-Side (default): All React components run on the client side.

2. Server-Side: Add 'use Server' as the first line of your component:
   

'use server';

export default async function requestUsername(formData) {
  const username = formData.get('username');
  return canRequest(username) ? 'successful' : 'failed';
}

Key Notes

• Server Components do not run on the client.

• Combined with Actions, they streamline tasks like form handling and API requests.

• Next.js users can already leverage server components; React 19 brings this directly to React.

3. ACTIONS

• Before React19: Manual Handling of Async states.

function handleSubmit() {
  setloading (true);
  try {
      const result = await saveData();
      setData(result);
      } 
  catch (err) 
     {
     setError(err);
     }
  finally
     {
     setloading(failse);
     } 
}

• After React19: Using useActionsState for clean async handling.

const [state, formAction] = useActionState(async (prevState, formData) => {
   const result = await saveData(formData);
   return result;
   }, null);

• Automatically Handles Loading, Errors and State updates.

4. NEW HOOKS

USEACTIONSTATE: FORM HANDLING

Automatically manages submission state and form validation.

• BEFORE REACT19:

const [isSubmitting, setIsSubmitting] = useState(false);

async function handleSubmit() {
  setIsSubmitting(true);
  try {
      await submitForm();
      }
  finally 
      {
      setIsSubmitting(false);
      }
}

• AFTER REACT19:

useActionState simplifies form submission.

const [state, formAction] = useActionState(async (prevState, formData) => {
    return await submitForm(formData);
});

USEFORMSTATUS: TRACK FORM STATUS

Access form states like pending, success or error.

const status = useFormStatus();

<button type = "submit" disabled = { status.pending }>
  { status.pending ? "Submitting..." : "Submit" } 
</button>

USEOPTIMISTIC: OPTIMISTIC UI UPDATES

Simplifies optimistic updates for better UX.

• BEFORE REACT19:

You updated UI optmistically, they handled reverts.

'use server';

export default async function requestUsername(formData) {
  const username = formData.get('username');
  return canRequest(username) ? 'successful' : 'failed';
}

• AFTER REACT19:

useOptimistic makes it declarative.

function handleSubmit() {
  setloading (true);
  try {
      const result = await saveData();
      setData(result);
      } 
  catch (err) 
     {
     setError(err);
     }
  finally
     {
     setloading(failse);
     } 
}

5. THE USE() HOOK

What is use()?

The use() hook simplifies async data fetching and context consumption by handling promises directly.

• BEFORE REACT19: USING USEEFFECT

Manual handling of async states.

const [state, formAction] = useActionState(async (prevState, formData) => {
   const result = await saveData(formData);
   return result;
   }, null);

• AFTER REACT19: THE USE() HOOK

Directly fetch async data and resolve promises

const [isSubmitting, setIsSubmitting] = useState(false);

async function handleSubmit() {
  setIsSubmitting(true);
  try {
      await submitForm();
      }
  finally 
      {
      setIsSubmitting(false);
      }
}

Advantages:

• No need for useEffect or useState.
• Cleaner and more declarative code.
• Handles promisis seamlessly.

6. SERVER COMPONENTS

What are Server Components?

Server Components render on the server and send lightweight results to the client, improving performance.

• BEFORE REACT19: TRADITIONAL CLIENT - SIDE RENDERING

You had to use useEffect for data fetching and SSR required complex tools.

const [state, formAction] = useActionState(async (prevState, formData) => {
    return await submitForm(formData);
});

• AFTER REACT19: SERVER - SIDE RENDERING

React Server Components integrate seamlessly.

const status = useFormStatus();

<button type = "submit" disabled = { status.pending }>
  { status.pending ? "Submitting..." : "Submit" } 
</button>

Advantages:

• Faster page loads (no heavy client-side JS).
• Improved SEO and reduced bundle size.

7. ENHANCED ASSET LOADING

React19 improves how assets like images and scritps load in the background.

• BEFORE REACT19:

You needed manual configurations.

function handleClick() {
 setItems([...items, newItem]);
 saveItem(newItem).catch(() => setItems(items)); // Revert on error
}

• AFTER REACT19: NATIVE LAZY LOADIING

Assets now load effeciently without intervention.

const [optimisticItems, addOptimisticItem] = useOptimistic(items);

function handleClick() {
 addOptimisticItem(newItem);
}

Advantages:

• Faster load times.
• Better user experience with reduced delays.

CONCLUSION

React 19 brings:

• Simplified async state management with Actions.
• New hooks like useActionState,
• useFormStatus and UseOptimistic.
• use() hook for easy async data handling.
• Seamless Server Components for better performance.
• Cleaner ref management and enhanced asset loading.

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