mongoDB, mongoose, cannot connect to DB - mongodb

Question

First time using mongoDB. Trying to connect to my cluster that i just created on atlas however i keep getting errors
keys.jss
module.exports = {
mongoURI: 'mongodb+srv://john:<********>#mern-shopping-i5abd.mongodb.net/testretryWrites=true&w=majority'
};
I might be following an outdated tutorial so certain things might be 'unnecessary'
const express = require('express');
const mongoose = require('mongoose');
const bodyParser = require('body-parser');
const app = express();
// Bodyparser Middleware
app.use(bodyParser.json());
// DB config
const db = require('./config/keys').mongoURI;
// Connect to Mongo
mongoose
.connect(db, {useNewUrlParser: true} )
.then(() => console.log('monogoDB Connected...'))
.catch(err => console.log(err));
const port = process.env.PORT || 5000;
app.listen(port, () => console.log('Server started on port ${port}'));
Rather than displaying port '5000' i would get an error (different each time)
message: '3rd parameter to mongoose.connect() or mongoose.createConnection() must be a function, got "object"',
name: 'MongooseError'

Answer 1

Here is how it would look with a function as a callback, instead of using promises. Notice that I also moved the app startup inside the callback function. This ensures that the app only starts up when we successfully connect to the DB.
I also moved the DB options (2nd parameter in the connect method), into a variable. This way, it's easy to find and can be modified in one place, if necessary. Ideally, you'd keep all your DB config in a single file, and reference it in other files as needed. Separate concerns :)
const mongoose = require('mongoose');
const bodyParser = require('body-parser');
const app = express();
// Bodyparser Middleware
app.use(bodyParser.json());
// DB config
const db = require('./config/keys').mongoURI;
const dbOptions = {useNewUrlParser: true, useUnifiedTopology: true};
// Connect to Mongo
mongoose
.connect(db, dbOptions, function(error) {
// we had an error of some kind
if (error) {
console.error(error);
// better yet, we don't want to app to run without our DB!
throw error;
}
// If we made it here, no errors came up
console.log('monogoDB Connected...');
// Start up the app!
const port = process.env.PORT || 5000;
app.listen(port, () => console.log(`Server started on port ${port}`));
});
Here is how it would look with the promise structure:
const express = require( "express" );
const mongoose = require( "mongoose" );
const bodyParser = require( "body-parser" );
const app = express();
// Bodyparser Middleware
app.use( bodyParser.json() );
// DB config
const db = require( "./config/keys" ).mongoURI;
const dbOptions = {useNewUrlParser: true, useUnifiedTopology: true};
// Connect to Mongo
mongoose
.connect( db, dbOptions )
.then( () => {
console.log( "monogoDB Connected..." );
// Start the application
const port = process.env.PORT || 5000;
app.listen( port, () => {
console.log( `Server started on port ${port}` );
} );
} )
.catch( err => {
console.log( err );
throw err;
} );