How to establish an connecting with mongoDB with Promise and .catch()

MongoDB Connection with Promise

//
// Use this template to establish connection to MongoDB with Promise to handle error
// See documentation at https://mongoosejs.com/docs/connections.html
// If initial connection fails, it will not attempt to reconnect.
// It will attempt to reconnect if there's error AFTER the initial successful connection.

mongoose.connect(process.env.DB_URI, {useNewUrlParser: true})
        .then(() => {
            console.log("MongoDB database initial connection established successfully.");
        })
        .catch((err) => {
            console.log("ERROR! Could not connect to Database!");
            console.log(err);
        });

//
// Use this to watch error events 
// See documentation at https://mongoosejs.com/docs/connections.html#error-handling
// i.e. mongoose.connection.on(EVENT_TYPE, ()=>{HANDLE_EVENTS_HERE});

const connection = mongoose.connection;
connection.on('disconnected',()=> {console.log('lost connection!')});
connection.on('reconnected',()=> {console.log('reconnected to db again!')});