{
        mongo1: {type: 'PRIMARY', tag: 'america'},
        mongo2: {type: 'SECONDARY', tag: 'europe'},
        mongo3: {type: 'SECONDARY', tag: 'africa'}
}

/*
 cfg = rs.conf();
 cfg.members[0].tags.continent = 'america'; // primary    - host = mongo1
 cfg.members[1].tags.continent = 'europe';  // secondary  - host = mongo2
 cfg.members[2].tags.continent = 'africa';  // secondary  - host = mongo3
 rs.reconfig(cfg);
 */

const mongodb = require('mongodb'),
    async = require('async'),
    MongoClient = mongodb.MongoClient,
    ReadPreference = mongodb.ReadPreference;


const
    MAP = {
        mongo1: {type: 'PRIMARY', tag: 'america'},
        mongo2: {type: 'SECONDARY', tag: 'europe'},
        mongo3: {type: 'SECONDARY', tag: 'africa'}
    },
    CONNECT_URL = 'mongodb://localhost:27017/folder',
    CONNECT_OPTIONS_LEGACY = {
        replicaSet: 'rs',
        readPreference: 'secondary',
        readPreferenceTags: [
            {
                "continent": "europe"
            }
        ]
    },
    CONNECT_OPTIONS_NEW = {
        replicaSet: 'rs',
        readPreference: new ReadPreference('secondary', [{
            "continent": "europe"
        }])
    };


function initConnection(options, cb) {
    MongoClient.connect(CONNECT_URL, options, function (err, db) {
        cb(err, db);
    })
}

function find(db, cb) {
    var filesCollection = db.collection('files');
    async.times(10, function (index, next) {
        filesCollection.find().explain(function (err, result) {
            console.log(index + ' - ' + result.serverInfo.host + ' - ' + MAP[result.serverInfo.host].type + ' ' + MAP[result.serverInfo.host].tag);
            next();
        });
    }, function () {
        cb();
    });
}

console.log('Start test!')
async.waterfall([
        function testLegacyOptions(cb) {
            console.log();
            console.log('Test options with readPreferenceTags!')
            console.log('Read preference: secondary!')
            console.log('Read preference tags: continent-europe!')
            initConnection(CONNECT_OPTIONS_LEGACY, cb);
        },
        find,
        function testNewOptions(cb) {
            console.log();
            console.log('Test options with replicaSet instance!')
            console.log('Read preference: secondary!')
            console.log('Read preference tags: continent-europe!')
            initConnection(CONNECT_OPTIONS_NEW, cb);
        },
        find
    ],
    function (err) {
        console.log();
        console.log('Testing done!')
    })

Start test!

Test options with readPreferenceTags!
Read preference: secondary!
Read preference tags: continent-europe!
the options [readPreferenceTags] is not supported
1 - mongo2 - SECONDARY europe
0 - mongo2 - SECONDARY europe
4 - mongo2 - SECONDARY europe
2 - mongo2 - SECONDARY europe
3 - mongo2 - SECONDARY europe
8 - mongo2 - SECONDARY europe
7 - mongo2 - SECONDARY europe
5 - mongo2 - SECONDARY europe
6 - mongo2 - SECONDARY europe
9 - mongo2 - SECONDARY europe

Test options with replicaSet instance!
Read preference: secondary!
Read preference tags: continent-europe!
0 - mongo1 - PRIMARY america
1 - mongo1 - PRIMARY america
2 - mongo1 - PRIMARY america
4 - mongo1 - PRIMARY america
3 - mongo1 - PRIMARY america
5 - mongo1 - PRIMARY america
7 - mongo1 - PRIMARY america
8 - mongo1 - PRIMARY america
9 - mongo1 - PRIMARY america
6 - mongo1 - PRIMARY america

Testing done!