api.ts

import Cors from 'cors'
import { NextApiHandler, NextApiRequest, NextApiResponse } from 'next'

const cors = Cors({
  methods: ['POST'],
})

function runMiddleware(req, res, fn) {
  return new Promise((resolve, reject) => {
    fn(req, res, result => {
      if (result instanceof Error) {
        return reject(result)
      }

      return resolve(result)
    })
  })
}

export default async (req: NextApiRequest, res: NextApiResponse) => {
  await runMiddleware(req, res, cors)
  res.status(200).json(['some', 'stuff'])
}