a.js

export let MY_SERVER = ''
export let DEV_SERVER = ''

export let API_ROOT = (process.env.NODE_ENV === 'production')
  ? MY_SERVER
  : DEV_SERVER

import {MY_SERVER, DEV_SERVER} from 'a.js'

MY_SERVER = '192.168.1.1'

DEV_SERVER = '192.168.1.2'

Module build failed: SyntaxError: "MY_SERVER" is read-only

如何修改MY_SERVER，DEV_SERVER 的值？

b.js

export var MY_SERVER = ''
export var DEV_SERVER = ''

export var API_ROOT = (process.env.NODE_ENV === 'production')
  ? MY_SERVER
  : DEV_SERVER

import {MY_SERVER, DEV_SERVER} from 'b.js'

MY_SERVER = '192.168.1.1'

DEV_SERVER = '192.168.1.2'

Module build failed: SyntaxError: "MY_SERVER" is read-only

如何修改MY_SERVER，DEV_SERVER 的值？