# Functions

Next.js function APIs.

Reference: https://nextjs.org/docs/app/api-reference/functions

## Navigation Hooks (Client)

| Hook                        | Purpose                                                        | Reference                                                                                |
| --------------------------- | -------------------------------------------------------------- | ---------------------------------------------------------------------------------------- |
| `useRouter`                 | Programmatic navigation (`push`, `replace`, `back`, `refresh`) | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-router)                   |
| `usePathname`               | Get current pathname                                           | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-pathname)                 |
| `useSearchParams`           | Read URL search parameters                                     | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-search-params)            |
| `useParams`                 | Access dynamic route parameters                                | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-params)                   |
| `useSelectedLayoutSegment`  | Active child segment (one level)                               | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-selected-layout-segment)  |
| `useSelectedLayoutSegments` | All active segments below layout                               | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-selected-layout-segments) |
| `useLinkStatus`             | Check link prefetch status                                     | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-link-status)              |
| `useReportWebVitals`        | Report Core Web Vitals metrics                                 | [Docs](https://nextjs.org/docs/app/api-reference/functions/use-report-web-vitals)        |

## Server Functions

| Function     | Purpose                                      | Reference                                                              |
| ------------ | -------------------------------------------- | ---------------------------------------------------------------------- |
| `cookies`    | Read/write cookies                           | [Docs](https://nextjs.org/docs/app/api-reference/functions/cookies)    |
| `headers`    | Read request headers                         | [Docs](https://nextjs.org/docs/app/api-reference/functions/headers)    |
| `draftMode`  | Enable preview of unpublished CMS content    | [Docs](https://nextjs.org/docs/app/api-reference/functions/draft-mode) |
| `after`      | Run code after response finishes streaming   | [Docs](https://nextjs.org/docs/app/api-reference/functions/after)      |
| `connection` | Wait for connection before dynamic rendering | [Docs](https://nextjs.org/docs/app/api-reference/functions/connection) |
| `userAgent`  | Parse User-Agent header                      | [Docs](https://nextjs.org/docs/app/api-reference/functions/userAgent)  |

## Generate Functions

| Function                | Purpose                                 | Reference                                                                           |
| ----------------------- | --------------------------------------- | ----------------------------------------------------------------------------------- |
| `generateStaticParams`  | Pre-render dynamic routes at build time | [Docs](https://nextjs.org/docs/app/api-reference/functions/generate-static-params)  |
| `generateMetadata`      | Dynamic metadata                        | [Docs](https://nextjs.org/docs/app/api-reference/functions/generate-metadata)       |
| `generateViewport`      | Dynamic viewport config                 | [Docs](https://nextjs.org/docs/app/api-reference/functions/generate-viewport)       |
| `generateSitemaps`      | Multiple sitemaps for large sites       | [Docs](https://nextjs.org/docs/app/api-reference/functions/generate-sitemaps)       |
| `generateImageMetadata` | Multiple OG images per route            | [Docs](https://nextjs.org/docs/app/api-reference/functions/generate-image-metadata) |

## Request/Response

| Function        | Purpose                        | Reference                                                                  |
| --------------- | ------------------------------ | -------------------------------------------------------------------------- |
| `NextRequest`   | Extended Request with helpers  | [Docs](https://nextjs.org/docs/app/api-reference/functions/next-request)   |
| `NextResponse`  | Extended Response with helpers | [Docs](https://nextjs.org/docs/app/api-reference/functions/next-response)  |
| `ImageResponse` | Generate OG images             | [Docs](https://nextjs.org/docs/app/api-reference/functions/image-response) |

## Common Examples

### Navigation

Use `next/link` for internal navigation instead of `<a>` tags.

```tsx
// Bad: Plain anchor tag
<a href="/about">About</a>;

// Good: Next.js Link
import Link from "next/link";

<Link href="/about">About</Link>;
```

Active link styling:

```tsx
"use client";

import Link from "next/link";
import { usePathname } from "next/navigation";

export function NavLink({ href, children }) {
  const pathname = usePathname();

  return (
    <Link href={href} className={pathname === href ? "active" : ""}>
      {children}
    </Link>
  );
}
```

### Static Generation

```tsx
// app/blog/[slug]/page.tsx
export async function generateStaticParams() {
  const posts = await getPosts();
  return posts.map(post => ({ slug: post.slug }));
}
```

### After Response

```tsx
import { after } from "next/server";

export async function POST(request: Request) {
  const data = await processRequest(request);

  after(async () => {
    await logAnalytics(data);
  });

  return Response.json({ success: true });
}
```
