next.js/examples/api-routes-rest/pages/api/user/[id].ts

import type { NextApiRequest, NextApiResponse } from "next";
import type { User } from "../../../interfaces";

export default function userHandler(
  req: NextApiRequest,
  res: NextApiResponse<User>,
) {
  const { query, method } = req;
  const id = parseInt(query.id as string, 10);
  const name = query.name as string;

  switch (method) {
    case "GET":
      // Get data from your database
      res.status(200).json({ id, name: `User ${id}` });
      break;
    case "PUT":
      // Update or create data in your database
      res.status(200).json({ id, name: name || `User ${id}` });
      break;
    default:
      res.setHeader("Allow", ["GET", "PUT"]);
      res.status(405).end(`Method ${method} Not Allowed`);
  }
}