mongo nodejs test

'use strict';

const connUri = 'mongodb://localhost:37017,localhost:37018,localhost:37019/test';
const connOpts = {
    db: {
        bufferMaxEntries: 0
    },
    server: {
        autoReconnect: true,
        socketOptions: {
            connectTimeoutMS: 1000 // for intial discovery of what is behind the connection string! all of the connection has to succeed so that the driver recognizes that the connection string isn't a mix of different topologies
        }
    },
    mongos: {
        poolSize: 1,
        socketOptions: {
            connectTimeoutMS: 1000
        }
    }
};
const queryTimeout = 1000;
const queryBackoff = 1000;

const MongoClient = require('mongodb').MongoClient;
const Logger = require('mongodb').Logger;

Logger.setLevel('debug'); // _

function startQuerying(db) {
    let now = Date.now();
    let timeout = setTimeout(function () {
        console.log(new Date().toISOString(), 'Query timed out, ms:', Date.now() - now);
        setTimeout(startQuerying, queryBackoff, db);
    }, queryTimeout);
    db.collection('test').findOne({}, function (err) {
        let elapsed = Date.now() - now;
        if (elapsed <= queryTimeout) { // don't handle timeout here
            if (err) {
                console.log(new Date().toISOString(), 'Query failed:', err, ', ms:', elapsed);
            } else {
                // if (elapsed > 10) {
                    console.log(new Date().toISOString(), 'Query successful in ms:', elapsed);
                // }
            }
            clearTimeout(timeout);
            setTimeout(startQuerying, queryBackoff, db);
        }
    });
}

MongoClient.connect(connUri, connOpts, function (err, db) {
    startQuerying(db);
});