How to use MongoDB with promises in Node.js?

You can also do async/await

async function main(){
 let client, db;
 try{
    client = await MongoClient.connect(mongoUrl, {useNewUrlParser: true});
    db = client.db(dbName);
    let dCollection = db.collection('collectionName');
    let result = await dCollection.find();   
    // let result = await dCollection.countDocuments();
    // your other codes ....
    return result.toArray();
 }
 catch(err){ console.error(err); } // catch any mongo error here
 finally{ client.close(); } // make sure to close your connection after
}

Your approach is almost correct, just a tiny mistake in your argument

var MongoClient = require('mongodb').MongoClient
var url = 'mongodb://localhost:27017/example'
MongoClient.connect(url)
  .then(function (db) { // <- db as first argument
    console.log(db)
  })
  .catch(function (err) {})