node_modules/mongoose/examples/promises/promise.js

// import async to make control flow simplier
var async = require('async');

// import the rest of the normal stuff
var mongoose = require('../../lib');

require('./person.js')();

var Person = mongoose.model('Person');

// define some dummy data
var data = [
  {
    name: 'bill',
    age: 25,
    birthday: new Date().setFullYear((new Date().getFullYear() - 25))
  },
  {
    name: 'mary',
    age: 30,
    birthday: new Date().setFullYear((new Date().getFullYear() - 30))
  },
  {
    name: 'bob',
    age: 21,
    birthday: new Date().setFullYear((new Date().getFullYear() - 21))
  },
  {
    name: 'lilly',
    age: 26,
    birthday: new Date().setFullYear((new Date().getFullYear() - 26))
  },
  {
    name: 'alucard',
    age: 1000,
    birthday: new Date().setFullYear((new Date().getFullYear() - 1000))
  }
];


mongoose.connect('mongodb://localhost/persons', function(err) {
  if (err) {
    throw err;
  }

  // create all of the dummy people
  async.each(data, function(item, cb) {
    Person.create(item, cb);
  }, function(err) {
    if (err) {
      // handle error
    }

    // create a promise (get one from the query builder)
    var prom = Person.find({age: {$lt: 1000}}).exec();

    // add a callback on the promise. This will be called on both error and
    // complete
    prom.addBack(function() {
      console.log('completed');
    });

    // add a callback that is only called on complete (success) events
    prom.addCallback(function() {
      console.log('Successful Completion!');
    });

    // add a callback that is only called on err (rejected) events
    prom.addErrback(function() {
      console.log('Fail Boat');
    });

    // you can chain things just like in the promise/A+ spec
    // note: each then() is returning a new promise, so the above methods
    // that we defined will all fire after the initial promise is fulfilled
    prom.then(function(people) {
      // just getting the stuff for the next query
      var ids = people.map(function(p) {
        return p._id;
      });

      // return the next promise
      return Person.find({_id: {$nin: ids}}).exec();
    }).then(function(oldest) {
      console.log('Oldest person is: %s', oldest);
    }).then(cleanup);
  });
});

function cleanup() {
  Person.remove(function() {
    mongoose.disconnect();
  });
}