Trying to understand how to create a Mongo document, in a nodeJS environment with upsert and $set in the same flow

append_to_set.js

  var MongoClient = require('mongodb').MongoClient;

MongoClient.connect('mongodb://127.0.0.1:27017/inbox', function(err, db) {
    if (err) throw err;
    var collection = db.collection('test_insert');
    var sample1 = { 'messages.82513': { body: '123\r\n456\r\n789\r\n', db_msg_id: '82513' } };
    var sample2 = { 'messages.12': { body: '123\r\n456\r\n789\r\n', db_msg_id: '12'} };
    var base_doc = { conv_hash: '711_34401',  messages: {} };

    //## FAILS ##
    collection.update({conv_hash: '711_34401'}, base_doc, {upsert: true }, function() {
          collection.update({conv_hash: '711_34401'}, {$set: sample1}, function(){
            collection.update({conv_hash: '711_34401'}, base_doc, {upsert: true }, function() {
                collection.update({conv_hash: '711_34401'}, {$set: sample2}, function(){
                  db.close();
               });
            });
         });
      });
    //### WORKS: ##
    //   collection.update({conv_hash: '711_34401'}, base_doc, {upsert: true }, function() {
    //     collection.update({conv_hash: '711_34401'}, {$set: sample1}, function(){
    //         collection.update({conv_hash: '711_34401'}, {$set: sample2}, function(){
    //           db.close();
    //        });
    //    });
    // });
});