required-env-vars.js

module.exports = (variables) => {
	if (!Array.isArray(variables)) {
		throw new Error('Variables must be an array')
	}
	const missing = variables
		.reduce((missing, current) => !process.env[variable] ? [...missing, current] : missing, [])

  if (missing.length > 0) {
	  const message = missing.length === 1 ?
		  `Missing environment variable ${missing[0]}`:
		  `Missing environment variables ${missing.join(', ')}`
	  throw new Error(message)
  }
}