output.txt

Opened mongoose connection
Successfully created and inserted new records
---------
Black 2016 BMW 135is
Silver 2016 BMW 335is
Red 2016 BMW 535is
Alpine White 2016 BMW M6
---------
UPDATED:
Japan Red 2016 BMW M6
---------
All done!
Closed mongoose connection

to-hell-with-callback-hell.js

'use strict';

var mongoose = require('mongoose');
mongoose.Promise = global.Promise;
var db = require('./db');
var Car = require('./car');

mongoose.connect('mongodb://localhost/cars');

function quit () {
  mongoose.disconnect();
  console.log('All done!');
}

// helper methods for our promises to call

const separator = () => {
  console.log('---------');
};

const createCars = () => {
  // `cars` here comes from our seed data
  return Car.create(cars);
};

const successMessage = res => {
  console.log('Successfully created and inserted new records');
  separator();
  return res;
};

const handleErrors = err => {
  console.log('ERROR: ', err);
  separator();
  return err;
};

// our seed data

let cars = [
  {make: 'BMW', model: '135is', year: 2016, color: 'Black'},
  {make: 'BMW', model: '335is', year: 2016, color: 'Silver'},
  {make: 'BMW', model: '535is', year: 2016, color: 'Red'},
  {make: 'BMW', model: 'M6', year: 2016, color: 'Alpine White'},
];

// we need to bulk insert the records for all of these cars

Car.remove({})                    // remove all previous records in the Cars collection
  .then(createCars)               // run our function for creating cars
  .then(successMessage)           // handle the success message?
  .then((res) => {                // iterate over our result set and print out the details
    res.map(car => car.print());
  })
  .then(() => {                   // start an anonymous function for handling the update
    let updates = { color: 'Japan Red' };
    let options = { new: true };

    // find a record and edit it, then return that record
    return Car.findOneAndUpdate({model: 'M6'}, updates, options);
  })
  .then((res) => {                // we are accepting the return of the last `then`
    separator();                  // this just prints out `---------` between actions

    console.log('UPDATED: ');     // more notifications about what happened
    res.print();                  // print details of edited record

    separator();                  // some more lines

    return res;                   // return the result of all of this
  })
  .catch(handleErrors);           // handle any errors that might have happened

setTimeout(function () {
  quit();
}, 2000);

I don't think you'd normally do something like this, at least not with a web app-- insertions, edits, and deletes would be handled in separate controller actions and whatnot. But its still a neat exercise in passing around promises and return values.

Very nice!