Simple Mongoose Schema

schema.js

var mongoose = require('mongoose');
mongoose.connect('mongodb://localhost/schematest');

var animalSchema = new mongoose.Schema({
  type: {type: String, required: true},
  age: Number,
  lastInspected: {type: Date, default: Date.now},
  name: {type: String, required: false}
});

animalSchema.methods.makeNoise = function(callback){
  var noise = "Some animals make noise";
  if (this.type == "Giraffe"){
    if (this.age < 2){
      noise = "Young giraffes can make a honking kind of sound.";
    } else {
      noise = "Elder giraffes do not make noise.";
    }
  }
  callback(noise);
};

animalSchema.statics.findBabies = function(callback){
  this.find({age: {$lt: 2}}, callback);
};

var Animal = mongoose.model('Animal', animalSchema);

var babyGiraffe = new Animal({ type: "Giraffe", age: 0});

babyGiraffe.save(function(err, baby){
  if (err) {
    console.log("Error: ",err);
  } else {
    console.log(baby);
    Animal.findBabies(console.log);
    baby.makeNoise(console.log);
  }
});