nextjs-handler-allowed-methods.ts

import type { NextApiRequest, NextApiResponse } from 'next';

type User = { userId: string };

const allowedMethods = ['GET'];

const handler = (req: NextApiRequest, res: NextApiResponse<User>) => {
  // If the req.method isn't included in the list of allowed methods we return a 405
  if (!allowedMethods.includes(req.method!) || req.method == 'OPTIONS') {
    return res.status(405).send({ message: 'Method not allowed.' });
  }

  return res.status(200).json({ userId: 'abc123' });
};
  
export default handler;