How to use the ms-rest-azure.AzureEnvironment.AzureUSGovernment function in ms-rest-azure

module.exports.getEnvironment = function(environmentName) {
  var azureEnv;
  switch(environmentName) {
    case 'AzureCloud':
        azureEnv = AzureEnvironment.Azure;
        break;
    case 'AzureChinaCloud':
        azureEnv = AzureEnvironment.AzureChina;
        break;
    case 'AzureGermanCloud':
        azureEnv = AzureEnvironment.AzureGermanCloud;
        break;
    case 'AzureUSGovernment':
        azureEnv = AzureEnvironment.AzureUSGovernment;
        break;
    default:
        throw new Error(util.format('Environment %s is not supported', environmentName));
  }

  var len = azureEnv.resourceManagerEndpointUrl.length;
  if (azureEnv.resourceManagerEndpointUrl[len - 1] != '/') {
    azureEnv.resourceManagerEndpointUrl = azureEnv.resourceManagerEndpointUrl + '/' ;
  }
  return azureEnv;
};