mongoose connect

                                    //Import the mongoose module
var mongoose = require('mongoose');

//Set up default mongoose connection
var mongoDB = 'mongodb://127.0.0.1/my_database';
mongoose.connect(mongoDB, {useNewUrlParser: true, useUnifiedTopology: true});

//Get the default connection
var db = mongoose.connection;

//Bind connection to error event (to get notification of connection errors)
db.on('error', console.error.bind(console, 'MongoDB connection error:'));

                                    mongoose.connect('mongodb://localhost:27017/test', {
  useMongoClient: true,
  connectTimeoutMS: 1000
})

                                    const mongoose = require('mongoose');

const connectDB = async () => {
    mongoose
        .connect('mongodb://localhost:27017/playground', {
            useCreateIndex: true,
            useNewUrlParser: true,
            useUnifiedTopology: true,
            useFindAndModify: false
        })
        .then(() => console.log('Connected Successfully'))
        .catch((err) => console.error('Not Connected'));
}

module.exports = connectDB;

                                    mongoose.connect('mongodb://username:password@host:port/database?options...', {useNewUrlParser: true});

                                    mongoose.connect('mongodb://username:password@host:port/database?options...', {useNewUrlParser: true});