cors.js

const express = require('express')
const app = express()
const cors = require('cors')
const port = 3000

app.use(cors(
   {
    exposedHeaders: ['token'],
   }
))

app.get('/ping', (req, res) => {
  res.header("token", "test token")
  res.json('Pong!')
})

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`)
})