async and promises

seeds_async.js

require('./db');

var Person = require('./person');
var Story = require('./story');

async function seed() {

  await Person.remove({});
  await Story.remove({});
  let user = new Person({ name: 'Herman Melville' });
  const story = await Story.create({ title: 'Moby Dick', _creator: user});
  user.stories.push(story);
  await user.save();
  let person = await Person.findOne({}).populate('stories').exec();
  return `${person.name} wrote ${person.stories[0].title}.`;

}

seed()
  .then(console.log)
  .catch(console.log)
  .then(process.exit);

seeds_callbacks.js

require('./db');
var Person = require('./person');
var Story = require('./story');

Person.remove({}, function(err){
  if (err) {
    console.log(err);
    process.exit();
  }
  Story.remove({}, function(err){
    if (err) {
      console.log(err);
      process.exit();
    }
    var user = new Person({ title: 'Herman Melville' });
    user.save(function(err){
      if (err) {
        console.log(err);
        process.exit();
      }
      var story = new Story({ title: 'Moby Dick' });
      story._creator = user;
      story.save(function(err){
        if (err) {
          console.log(err);
          process.exit();
        }
        user.stories.push(story);
        user.save(function(err){
          if (err) {
            console.log(err)
            process.exit();
          }
          Person.findOne({}).populate('stories').exec(function(err, person){
            if (err) {
              console.log(err)
              process.exit();
            }
            console.log(`${person.name} wrote ${person.stories[0].title}.`);
            process.exit();
          });
        });
      });
    });
  });
});

seeds_promises.js

require('./db');

var Person = require('./person');
var Story = require('./story');

Promise.all([

  Person.remove({}), 
  Story.remove({})

])
.then(() => {

  var user = new Person({ name: 'Herman Melville' });
  var story = new Story({ title: 'Moby Dick', _creator: user });
  user.stories.push(story);

  return Promise.all([
    story.save(), 
    user.save() 
  ]);
})
.then(() => {

  return Person.findOne({}).populate('stories').exec() 

})
.then((person) => {

  console.log(`${person.name} wrote ${person.stories[0].title}.`);

})
.catch(console.log)
.then(process.exit);