NodeJS Mongoose handle database connection failed exception

I'm building a restful web service api using NodeJS.It uses Mongoose as ODM and using MongoDB for backend. Below i will explain my scenario

I started nodejs server After that i shutdown the MongoDB database. Then call the GET api call,it doest catch any errors and api call get hang.

database config in main.js file

var mongoose = require('mongoose');
var uri = 'mongodb://localhost/mydb';
mongoose.Promise = global.Promise;
var options = { server: {socketOptions: { keepAlive: 300000, connectTimeoutMS: 10000 } } } ;
mongoose.connect(uri,options);
var db = mongoose.connection;
db.on('error',console.log.bind(console,'connection refused !!!!!'));
db.once('open', console.log.bind(console,'connection success !!!!!'));

this is my basic GET call

 var express = require('express');
    var router = express.Router();
    var mongoose = require('mongoose');
    var rootRes = require('../model/rootresources.js');

    router.get('/', function(req, res, next) {
      rootRes.find({},function (err, rootResource) {
    if (err){
     console.log('Error occurd !!!') }
    res.json(rootResource);
});
});

Even database connection failed, the code does not goes to error block. So didn't capture the database refuse when database connection is failed in the API call.

I want to capture that error and send internal server error (code:500) to client. I tried to find the solution but still could not find it Any solutions or do i made a mistake ?

Thank you Amila

via Amila