mongo-singleton.js

const MongoClient = require('mongodb').MongoClient
const url = `mongodb://root:mo1542653!@localhost:27017/?authMechanism=SCRAM-SHA-1&authSource=admin`

var _connInstance

const getInstance = async () => {
    if (!_connInstance) {
        _connInstance = await getConnection()
    }
    return _connInstance
}

const getConnection = async () => {
    return await MongoClient.connect(url, { useNewUrlParser: true, poolSize: 5 })
}

exports.getInstance = getInstance