How do I get query string params in NextJS middleware

nextUrl object already includes searchParams which is a valid URLSearchParams instance.

E.G. usage

export function middleware(req: NextRequest) {
    if(req.nextUrl.searchParams.get('flag')) {
        return NextResponse.rewrite('/feature');
    }
}

As @j-cue said above but I also discovered you can get search from nextUrl.

e.g.

export const middleware = (request) => {
  const { nextUrl: { search } } = request;
  const urlSearchParams = new URLSearchParams(search);
  const params = Object.fromEntries(urlSearchParams.entries());
};

As of Next.js 13.4 you can get search params like this from the url:

export const GET = async (request, { params }) => {
   try{
        
        // Path Params are received from {params} variable
        //You can receive search params as below:
        // UrlPath = `/api/prompt/${post._id.toString()}?type=DELETE`
        //The search params [type, method] for above url

        const {type, method} = Object.fromEntries(request.nextUrl.searchParams);
        console.log(type, method);
        if(type === "DELETE" && method === "GET"){
            //Perform an action
        }

        return new Response("Action performed", {status: 200});
   }
   catch(err){
    console.log(err);
   }
}

Try this one :

export async function GET(req: Request, route: { params: { id: 
string } }) {
const id: number = Number(route.params.id);
return new Response(JSON.stringify({ id }), { status: 200 });
}