Wrap firebase-functions with specified region.

baseFunctions.ts

import * as f from 'firebase-functions'

const functions = (runtimeOptions: f.RuntimeOptions = {}) =>
  f.runWith(runtimeOptions).region('asia-northeast1')

export default functions

user.ts

import functions from '../util/baseFunctions'

export const onCreate = functions({ memory: '512MB' })
  .firestore.document('/users/{userID}')
  .onCreate(async (snapshot, context) => {
    //...
  })