How to use Moment.js with Mongoose's Virtuals

moment-mongoose-virtuals.js

var moment = require('moment')
  , dateMask = 'YYYY-MM-DD';

var MeetingSchema = new Schema({
   ...
});

MeetingSchema
  .virtual('startDate_yyyymmdd')
  .get(function () {
    return moment(this.startDate).format(dateMask);
  });