const client = await MongoClient.connect('mongodb://user:pass@host/mydb', {
    useNewUrlParser: true
})

const db = await client.db('mydb')

const db = await client.db() // mydb is used

const url = require('url')
const { MongoClient } = require('mongodb')

const mongodbServerUrl = 'mongodb://user:pass@host/mydb'
const mongoPathName = url.parse(mongodbServerUrl).pathname
const dbName = mongoPathName.substring(mongoPathName.lastIndexOf('/') + 1)

const client = await MongoClient.connect(mongodbServerUrl, {
    useNewUrlParser: true
})

const db = await client.db(dbName)