Javascript singleton in ES6

.log

TCL: -------------------------------------
TCL: main -> db1 === db2 true
TCL: main -> db1 === db3 true
TCL: -------------------------------------

main.js

import { resetCollection, getDatabase } from './mongo'

import { test } from './test'

async function main() {
    const db1 = await getDatabase()
    const db2 = await getDatabase()
    const db3 = await test()

    console.log('TCL: -------------------------------------');
    console.log('TCL: main -> db1 === db2', db1 === db2);
    console.log('TCL: main -> db1 === db3', db1 === db3);
    console.log('TCL: -------------------------------------');
}

main()

mongo.js

import { MongoClient } from 'mongodb'

const databaseName = 'foo'

let _singletonClient = null

export async function getDatabase() {
  const client = await getClient()
  const mongoDb = client.db(databaseName)
  return mongoDb
}

export async function getClient() {
  if (!_singletonClient) { _singletonClient = await connectClient() }
  return _singletonClient
}

export async function resetCollection(collectionName: string) {
  const db = await getDatabase()
  await db.createCollection(collectionName)
  const collection = db.collection(collectionName)
  await collection.drop()
  return collection
}

async function connectClient() {
  console.log('-------------------------- Initiating MongoDB connection')
  const uri = 'mongodb://localhost:27017'
  const mongoClient = await MongoClient.connect(uri, { useNewUrlParser: true })
  return mongoClient
}

test.js

import { resetCollection, getDatabase } from './mongo'

export async function test() {
  const db = await getDatabase()
  return db
}