How to establish connection between MongoDB and your Node.js backend using environmental variables

app.js

const url = `mongodb+srv://${process.env.DB_USER}:${process.env.DB_PASSWORD}@cluster0-usg5d.mongodb.net`+
    `/${process.env.DB_NAME}?retryWrites=true&w=majority`;
mongoose
    .connect( url, { useNewUrlParser: true, useCreateIndex: true, useUnifiedTopology: true })
    .then(() =>{
        app.listen(5000);
    })
    .catch(err => console.log( err ));