Mongoose Connection

The safest way to do this, it to "listen for the connect event". This way you don't care how long it takes for the DB to give you a connection.

Once that is done - you should start the server. Also.. config.MONGOOSE is exposed across your app, so you only have one DB connection.

If you want to use mongoose's connection, simply require config in your module, and call config.Mongoose. Hope this helps out someone!

Here's the code.

var mongoURI; mongoose.connection.on("open", function(ref) { console.log("Connected to mongo server."); return start_up(); }); mongoose.connection.on("error", function(err) { console.log("Could not connect to mongo server!"); return console.log(err); }); mongoURI = "mongodb://localhost/dbanme"; config.MONGOOSE = mongoose.connect(mongoURI); 

Mongoose connection using Singleton Pattern

Mongoose Connection File - db.js

//Import the mongoose module const mongoose = require('mongoose'); class Database { // Singleton connection = mongoose.connection; constructor() { try { this.connection .on('open', console.info.bind(console, 'Database connection: open')) .on('close', console.info.bind(console, 'Database connection: close')) .on('disconnected', console.info.bind(console, 'Database connection: disconnecting')) .on('disconnected', console.info.bind(console, 'Database connection: disconnected')) .on('reconnected', console.info.bind(console, 'Database connection: reconnected')) .on('fullsetup', console.info.bind(console, 'Database connection: fullsetup')) .on('all', console.info.bind(console, 'Database connection: all')) .on('error', console.error.bind(console, 'MongoDB connection: error:')); } catch (error) { console.error(error); } } async connect(username, password, dbname) { try { await mongoose.connect( `mongodb+srv://${username}:${password}@cluster0.2a7nn.mongodb.net/${dbname}?retryWrites=true&w=majority`, { useNewUrlParser: true, useUnifiedTopology: true } ); } catch (error) { console.error(error); } } async close() { try { await this.connection.close(); } catch (error) { console.error(error); } } } module.exports = new Database(); 

call the connection from app.js

const express = require("express"); // Express Server Framework const Database = require("./utils/db"); const app = express(); Database.connect("username", "password", "dbname"); module.exports = app; 

I had the same error popping up. Then I found out that I didn't have a mongod running and listening for connections. To do that you just need to open another command prompt (cmd) and run mongod

Mongoose's default connection logic is deprecated as of 4.11.0. It is recommended to use the new connection logic:

• useMongoClient option
• native promise library

Here is the example from npm module: mongoose-connect-db

// Connection options const defaultOptions = { // Use native promises (in driver) promiseLibrary: global.Promise, useMongoClient: true, // Write concern (Journal Acknowledged) w: 1, j: true }; function connect (mongoose, dbURI, options = {}) { // Merge options with defaults const driverOptions = Object.assign(defaultOptions, options); // Use Promise from options (mongoose) mongoose.Promise = driverOptions.promiseLibrary; // Connect mongoose.connect(dbURI, driverOptions); // If the Node process ends, close the Mongoose connection process.on('SIGINT', () => { mongoose.connection.close(() => { process.exit(0); }); }); return mongoose.connection; } 

A simple way i make a connection:

const mongoose = require('mongoose')

mongoose.connect(<connection string>); mongoose.Promise = global.Promise; mongoose.connection.on("error", error => { console.log('Problem connection to the database'+error); });