Traits in JavaScript with CommonJS Modules

birds.js

var rolesComposition = require('./trait');

function Duck(swimMessage, flyMessage){
  this.swimMessage = swimMessage;
  this.flyMessage = flyMessage;
}

Duck.prototype = rolesComposition(require('./swimming'), require('./flying'));

function Penguin(swimMessage){
  this.swimMessage = swimMessage;
}

Penguin.prototype = rolesComposition(require('./swimming'));

flying.js

exports.flyMessage = 'default fly message';

exports.fly = function(){
  console.log(this.flyMessage);
};

swimming.js

exports.swim = function(){
  console.log(this.swimMessage);
};

trait.js

function mixin(target, source){
  Object.keys(source).forEach(function(key){
    target[key] = source[key];
  });
  
  return target;
}

function array(object){
  return Array.from ? Array.from(object) : Array.prototype.slice.call(object);
}

function rolesComposition(){
  return array(arguments).reduce(mixin, {});
}

module.exports = rolesComposition;