index.js

const functions = require("firebase-functions")
const cors = require("cors")

exports.iowa = functions.region("us-central1").https.onRequest((req, res) => {
  return cors()(req, res, () => {
    res.send("Hi from Iowa, USA")
  })
})

exports.london = functions
  .region("europe-west2")
  .https.onRequest((req, res) => {
    return cors()(req, res, () => {
      res.send("Hi from London, UK")
    })
  })

exports.hongkong = functions
  .region("asia-east2")
  .https.onRequest((req, res) => {
    return cors()(req, res, () => {
      res.send("Hi from Hongkong, Hongkong")
    })
  })

exports.seoul = functions
  .region("asia-northeast3")
  .https.onRequest((req, res) => {
    return cors()(req, res, () => {
      res.send("Hi from Seoul, Korea")
    })
  })