NodeJS - MongoDB - creating new user with admin privileges

mongo-create-user.js

var MongoClient = require('mongodb').MongoClient

//
//  config
//

var mongoPort    = '27017'
var mongoHost    = 'localhost'

var dbName       = 'dbName'
var userName     = 'admin'
var userPassword = 'pass1'

//
//  start
//

MongoClient.connect('mongodb://'+mongoHost+':'+mongoPort+'/'+dbName,
  function(err, db) {

  if (err){
    return console.log('Error: could not connect to mongodb')
  }

  // Use the admin database for the operation
  var adminDb = db.admin()

  // Add the new user to the admin database
  adminDb.addUser(userName, userPassword, {
      roles:  [{
        role : "userAdmin",
        db   : dbName
        }]
    },
    function(err, result) {

    if (err){
      return console.log('Error: could not add new user')
    }

    // Authenticate using the newly added user
    adminDb.authenticate(userName, userPassword, function(err, result) {

      if (err){
        return console.log('Error: could authenticate with created user')
      }

      console.log('Ok')
      db.close()
    })
  })
})