# Async Patterns

In Next.js 15+, `params`, `searchParams`, `cookies()`, and `headers()` are asynchronous.

## Async Params and SearchParams

Always type them as `Promise<...>` and await them.

### Pages and Layouts

```tsx
type Props = { params: Promise<{ slug: string }> };

export default async function Page({ params }: Props) {
  const { slug } = await params;
}
```

### Route Handlers

```tsx
export async function GET(request: Request, { params }: { params: Promise<{ id: string }> }) {
  const { id } = await params;
}
```

### SearchParams

```tsx
type Props = {
  params: Promise<{ slug: string }>;
  searchParams: Promise<{ query?: string }>;
};

export default async function Page({ params, searchParams }: Props) {
  const { slug } = await params;
  const { query } = await searchParams;
}
```

### Synchronous Components

Use `React.use()` for non-async components:

```tsx
import { use } from "react";

type Props = { params: Promise<{ slug: string }> };

export default function Page({ params }: Props) {
  const { slug } = use(params);
}
```

### generateMetadata

```tsx
type Props = { params: Promise<{ slug: string }> };

export async function generateMetadata({ params }: Props): Promise<Metadata> {
  const { slug } = await params;
  return { title: slug };
}
```

## Async Cookies and Headers

```tsx
import { cookies, headers } from "next/headers";

export default async function Page() {
  const cookieStore = await cookies();
  const headersList = await headers();

  const theme = cookieStore.get("theme");
  const userAgent = headersList.get("user-agent");
}
```

## Migration Codemod

```bash
npx @next/codemod@latest next-async-request-api .
```
