Creating a user in another db

Hello. I am trying to create a new user to access a new DB. I connect using a root user to the admin db and then I try to create a new user on a new db…

MongoClient.connect( process.env.JEST_MONGODB_URL, function( err, client ) {
    if ( err ) return console.error( err );
    const admin = new Admin( client.db( process.env.MONGODB_DATABASE ) );
        process.env.MONGODB_PASSWORD, {
            roles: [
                    role: 'readWrite',
                    db: process.env.MONGODB_DATABASE
        function( err, result ) {
            if ( err ) return console.error( err );
            console.log( result );

Im using here client.db() and passing that to new Admin() because I thought that would create the user in that db, but its creating it in the admin db instead.

In the code above, JEST_MONGODB_URL is a url like : mongodb://root:password123@mongodb-primary,mongodb-secondary:27017/admin?replicaSet=myset

amd MONGODB_DATABASE is a brand new db name like fubar

When I use the mongo shell I can use fubar and then create the new user and that works fine. How can I do this with mongodb native driver for node?