Example of how to connect to a mongodb 3.4 replica set from nodejs

mongodb-replicaset.js

const MongoClient = require('mongodb')

// here we create the url connection string that the driver needs
const getMongoURL = (options) => {
  const url = options.servers
    .reduce((prev, cur) => prev + `${cur.ip}:${cur.port},`, 'mongodb://')

  return `${url.substr(0, url.length - 1)}/${options.db}`
}

// mongoDB function to connect, open and authenticate
const connect = (options, mediator) => {
  mediator.once('boot.ready', () => {
    MongoClient.connect( getMongoURL(options), {
        db: options.dbParameters(),
        server: options.serverParameters(),
        replset: options.replsetParameters(options.repl)
      }, (err, db) => {
        if (err) {
          mediator.emit('db.error', err)
        }

        db.admin().authenticate(options.user, options.pass, (err, result) => {
          if (err) {
            mediator.emit('db.error', err)
          }
          mediator.emit('db.ready', db)
        })
      })
  })
}

module.exports = Object.assign({}, {connect})