1190.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var assert = require('assert')

console.log('\n===========');
console.log('    mongoose version: %s', mongoose.version);
console.log('========\n\n');

var dbname = 'testing_1190';
console.log('dbname: %s', dbname);
mongoose.connect('localhost', dbname);
mongoose.connection.on('error', function () {
  console.error('connection error', arguments);
});

var schema = new Schema({
    name: String
  , names: [{ name: String }]
});

var A = mongoose.model('A', schema);

mongoose.connection.on('open', function () {
  mongoose.set('debug', true);

  var a = new A({ name: '1190', names: [{ name: 'palm' }] });

  a.save(function (err, a) {
    if (err) return done(err);

    var newName = { _id: a.names[0]._id, name: 'evergreen' };
    A.update({ _id: a.id, 'names._id': a.names[0]._id }, { $set: { 'names.$': newName }}, function (err) {
      if (err) return done(err);

      console.log('update', arguments);

      A.findById(a, function (err, doc) {
        console.error('found', doc);
        done(err);
      });
    });
  })
});

function done (err) {
  if (err) console.error(err.stack);
  mongoose.connection.db.dropDatabase(function () {
    mongoose.connection.close();
  });
}