docs: Add JS/TS code switchers to Middleware (#54726)

In case a user needs a `js` code

docs/02-app/01-building-your-application/01-routing/11-middleware.mdx

@@ -15,7 +15,7 @@ Use the file `middleware.ts` (or `.js`) in the root of your project to define Mi
 
 ## Example
 
-```ts filename="middleware.ts"
+```ts filename="middleware.ts" switcher
 import { NextResponse } from 'next/server'
 import type { NextRequest } from 'next/server'
 
@@ -30,6 +30,20 @@ export const config = {
 }
 ```
 
+```js filename="middleware.js" switcher
+import { NextResponse } from 'next/server'
+
+// This function can be marked `async` if using `await` inside
+export function middleware(request) {
+  return NextResponse.redirect(new URL('/home', request.url))
+}
+
+// See "Matching Paths" below to learn more
+export const config = {
+  matcher: '/about/:path*',
+}
+```
+
 ## Matching Paths
 
 Middleware will be invoked for **every route in your project**. The following is the execution order:
@@ -98,7 +112,7 @@ Read more details on [path-to-regexp](https://github.com/pillarjs/path-to-regexp
 
 ### Conditional Statements
 
-```ts filename="middleware.ts"
+```ts filename="middleware.ts" switcher
 import { NextResponse } from 'next/server'
 import type { NextRequest } from 'next/server'
 
@@ -113,6 +127,20 @@ export function middleware(request: NextRequest) {
 }
 ```
 
+```js filename="middleware.js" switcher
+import { NextResponse } from 'next/server'
+
+export function middleware(request) {
+  if (request.nextUrl.pathname.startsWith('/about')) {
+    return NextResponse.rewrite(new URL('/about-2', request.url))
+  }
+
+  if (request.nextUrl.pathname.startsWith('/dashboard')) {
+    return NextResponse.rewrite(new URL('/dashboard/user', request.url))
+  }
+}
+```
+
 ## NextResponse
 
 The `NextResponse` API allows you to: