singleton mongo connector

mongoConnector.js

var MongoClient = require('mongodb').MongoClient
var db;

module.exports = {
    connect: connect
};

async function connect(url) {
    if (db) return db;
    const client = await MongoClient.connect("mongodb://localhost:27017/", { useUnifiedTopology: true });
    db = client.db("estudio");
    return db;
}

/**
* to use
*/
mongo.connect().then(client => client.collection("apellido").find({}, { projection: { _id: 0 } }).toArray()
                     .then(data => res.status(200).json(data)));