mongoose error in connecting to mongodb after adding user authentication to mongodb

Question

I am using mongodb on ubuntu 14.04 and I ran a command to add a user to a database and set readWrite permissions to it by the following command -

mongo

and then use utthan-dev and then do

db.createUser(
    {
      user: "hladdha",
      pwd: "Hladdha@31",
      roles: [
         { role: "readWrite", db: "utthaan-dev" }
      ]
    }
)

Now, I am connecting in my express app by the following connection string -

mongoose.connect('mongodb://hladdha:Hladdha@Demo@localhost/utthaan-dev');
mongoose.connection.on('error', function(err) {
    console.error('MongoDB connection error: ' + err);
    process.exit(-1);
    }
);

And now I am getting the following error in node console -

MongoDB connection error: MongoError: getaddrinfo ENOTFOUND

How should I connect the mongoose to mongodb correctly no ?