* fix internal type
* allow `void` to be returned from Middleware
* mark deprecated APIs in JSDoc
* fix typo
* add missing error page
* remove unused import
This PR moves the internal logic associated with `req.ua` into an explicit method the user should to call to have the same behavior.
**before**
```typescript
// middleware.ts
import { NextRequest, NextResponse } from 'next/server'
export function middleware(request: NextRequest) {
const url = request.nextUrl
const viewport = request.ua.device.type === 'mobile' ? 'mobile' : 'desktop'
url.searchParams.set('viewport', viewport)
return NextResponse.rewrites(url)
}
```
**after**
```typescript
// middleware.ts
import { NextRequest, NextResponse, userAgent } from 'next/server'
export function middleware(request: NextRequest) {
const url = request.nextUrl
const { device } = userAgent(request)
const viewport = device.type === 'mobile' ? 'mobile' : 'desktop'
url.searchParams.set('viewport', viewport)
return NextResponse.rewrites(url)
}
```
This potentially will save the extra 17 kB related to the size of `ua-parser-js`
