React 19 Cheat Sheet
# React 19 Cheat Sheet
## Hooks
```jsx
const [state, setState] = useState(init);
const ref = useRef(initial);
useEffect(() => {}, [deps]);
useMemo(() => value, [deps]);
useCallback(fn, [deps]);
useContext(Ctx);
useTransition(); // [isPending, startTransition]
useDeferredValue(value);
useOptimistic(state, fn);
useActionState(action, init);
```
## Server Components (RSC)
```jsx
// Default: Server Component
async function Page() {
const data = await fetch(...);
return <ClientComp data={data} />;
}
```
## Client Components
```jsx
'use client';
import { useState } from 'react';
```
## Server Actions
```jsx
async function addItem(formData) {
'use server';
await db.insert(...);
revalidatePath('/list');
}
<form action={addItem}>
```
## Metadata
```tsx
export const metadata = {
title: 'Page',
description: '...',
openGraph: { title: '...' },
};
```
## Route Handlers
```ts
export async function GET(req) { ... }
export async function POST(req) { ... }
```