connect_to_collection.js

//DB and authentication
mongo.connect(process.env.DATABASE_URL, (err, cluster) => {

   if(err) {
     console.log('Database error: ' + err);
   } else {

     // 1- connecting to the cluster
     console.log('Successful database connection');


     // 2- connetcing to the database
     const db = cluster.db(DATABASE_NAME);


     // 3- conneting to the collection
     const coll = db.collection(COLLECTION_NAME);


     //do your stuff on the collection here.

  }

});