env.js

const envConfig =  {
	development: {
		SITE_URL: 'http://localhost:3000',
		API_URL: 'http://localhost:3000/api'
	},
	testing: {
		SITE_URL: 'https://test.site.com',
		API_URL: 'https://api.test.site.com'
	},
	production: {
		SITE_URL: 'https://site.com',
		API_URL: 'https://api.site.com'
	}
}

const currentEnv = process.env.NODE_ENV
export default envConfig[currentEnv]

/*
 ---- USE IN COMPONENETS JS ----
 import env from './env'
 console.log(env.SITE_URL)
*/

/*
 ---- RUN SCRIPTS (package.json) ----
 ...
  "scripts": {
    "dev": "NODE_ENV=development ...",
    "testing": "NODE_ENV=testing ...",
    "build": "NODE_ENV=production ...",
  },
  ...
*/