Traits for AngularJS controllers

cowModule.js

angular.module('cowModule').factory('cowTrait', function() {
  
  // Private function (not available to controller using this trait)
  function getSound() {
    return 'Moo';
  }
  
  // Public properties & methods for use as a trait
  return {
    cows: 0,
    
    addCow: function() {
      this.cows++;
    }
    
    // Methods have full access to controller object as `this` (including bindings like `color`)
    getHorseSounds: function() {
      return this.cows + ' cows say ' + getSound() + ' in the ' + this.color + ' barn.';
    }
  };
});

farmModule.js

angular.module('farmModule', ['cowModule', 'horseModule']); // require modules whose traits we want to use

angular.module('farmModule').component('barn', {
  bindings: {color: '<'},
  // Declare controller and import traits (via service injection)
  controller: function($scope, cowTrait, horseTrait) {
    
    // This adds all properties of cowTrait & horseTrait to the controller object
    // (ctrl === this, it's just a local reference; handy for use within functions with a different `this` binding)
    var ctrl = angular.extend(this, cowTrait, horseTrait);
    
    // Private function is not available to the traits
    function countAnimals() {
      return ctrl.cows + ctrl.horses;
    }
    
    this.$onInit = function() {
      this.addCow();
      this.addHorse();
      alert(countAnimals() + ' animals in the ' + ctrl.color + ' barn.');
    }
  }
});

horseModule.js

angular.module('horseModule').factory('horseTrait', function() {
  
  // Private function (not available to controller using this trait)
  function getSound() {
    return 'Neigh';
  }
  
  // Public properties & methods for use as a trait
  return {
    horses: 0,
    
    addHorse: function() {
      this.horses++;
    }
    
    // Methods have full access to controller object as `this` (including bindings like `color`)
    getHorseSounds: function() {
      return this.horses + ' horses say ' + getSound() + ' in the ' + this.color + ' barn.';
    }
  };
});