Helper function for required parameters, from http://tinyurl.com/ychkf5oq

requiredParam.js

function requiredParam (param) {
  const requiredParamError = new Error(
   `Required parameter, "${param}" is missing.`
  )
  // preserve original stack trace
  if (typeof Error.captureStackTrace === ‘function’) {
    Error.captureStackTrace(
      requiredParamError, 
      requiredParam
    )
  }
  throw requiredParamError
}

/*
function findUsersByRole ({
  role = requiredParam('role'),
  withContactInfo, 
  includeInactive
} = {}) {...}
*/