I have created a mongodb native connection and saved it and then using findOne to query a document.

const Promise = require("bluebird");
const MongoClient = require('mongodb').MongoClient;
let mongoDB = undefined;

const getCollection = (collName) => {
    if (mongoDB) {
        return Promise.resolve(mongoDB.collection(collName));
    } else {
        return MongoClient.connect(EXT_CONFS.MONGODB_URL)
            .then(db => {
                mongoDB = db;
                return Promise.resolve(mongoDB.collection(collName));
            }).catch(e => {
               console.error('Error in MongoDb connection');
            });
    }
};

const findOne = (collName, filter, options) => {
    return getCollection(collName)
        .then(collection => {
            return collection.findOne(filter, options);
        })
        .then(doc => {
            return Promise.resolve(doc);
        }).catch(e => {
            console.error(e);
            return Promise.reject(e);
        });
};

Now this all works fine, but if Mongo ShutsDown / Fails after db client is cached, There is no way to handle error. Error never goes to any catch handler :

console.error('Error in MongoDb connection');

or

console.error(e);

I even tried events :

 mongoDB.on('connecting', function () {
     console.log('connecting');
 });
 mongoDB.on('timeout', function (error) {
     console.log('timeout!');
 });
 mongoDB.on('close', function (error) {
     console.log('close!');
 });
 mongoDB.on('error', function (error) {
     console.error('Error in MongoDb connection: ' + error);
 });
 mongoDB.on('connected', function () {
     console.log('connected!');
 });
 mongoDB.on('connection', function () {
     console.log('connected!');
 });
 mongoDB.on('connect', function () {
     console.log('connected!');
 });
 mongoDB.once('open', function () {
     console.log('connection open');
 });
 mongoDB.on('reconnected', function () {
     console.log('reconnected');
 });
 mongoDB.on('disconnected', function () {
     console.log('disconnected');
 });

but no success still. Using NodeJS 4.5.0, MongoDB-Native driver 2.2.24