update_db.js

var Twit = require('twit')
var twitter = new Twit({
    consumer_key: 'xxx',
    consumer_secret: 'xxx',
    access_token: 'xxx',
    access_token_secret: 'xxx',
    timeout_ms: 60 * 1000, // optional HTTP request timeout to apply to all requests.
    strictSSL: true, // optional - requires SSL certificates to be valid.
})

var GoogleSheets = require('google-drive-sheets');
var mySheet = new GoogleSheets('xxx');

const MongoClient = require('mongodb').MongoClient;
const uri = "mongodb+srv://xxx:xxx@edutwitter-1-jkgue.mongodb.net/test?retryWrites=true&w=majority";
const client = new MongoClient(uri, { useNewUrlParser: true });
  client.connect(err => {

    mySheet.getRows(1, function(err, rowData) {
        console.log('Pulled in ' + rowData.length + ' rows from Google Sheets');

        for (i = 0; i < rowData.length; i++) {
            let specialism = rowData[i].specialism
            let handle = rowData[i].twitterhandle

                  const collection = client.db("teachers_test").collection("teachers_test");
 
                      collection.findOne({screen_name: handle}, (err, data) => {
                      
                      if(data === null){
                            twitter.get('users/show', {screen_name: handle}, function(err, data, response) {

                            if (typeof data.screen_name === "undefined") {
                              console.log(handle + " - This user does not exist on twitter")
                            } else {

                            Object.assign(data, {specialism: specialism});
                                                         
                                 key = {'_id':data.id_str}

                                 collection.update(key, data, {upsert:true})
                                 console.log(handle + " added to the DB.")           
                             }
                        })
                      } else {
                        console.log("This user is already on the DB")
                      }
                    })
            }
        })

 })