serverless and connections mongodb atlas

1const mongoose = require('mongoose');
2mongoose.Promise = global.Promise;
3let isConnected;
4
5module.exports = connectToDatabase = () => {
6  if (isConnected) {
7    console.log('=> using existing database connection');
8    return Promise.resolve();
9  }
10
11  console.log('=> using new database connection');
12  return mongoose.connect(process.env.DB)
13    .then(db => { 
14      isConnected = db.connections[0].readyState;
15    });
16};