private members using Function.prototype.bind

gistfile1.js

function create(behaviors, context) {
  return Object.getOwnPropertyNames(behaviors).reduce(function(obj, name) {
    obj[name] = behaviors[name].bind(context);
    return obj;
  }, {});
}

var Gadget = {
  getName: function () {
    return this.name;
  },
  getColor: function () {
    return this.color;
  }
};

var toy = create(Gadget, {name: 'iPod', color: 'black'});

console.log(toy.name);        // undefined;
console.log(toy.color);       // undefined;
console.log(toy.getName());   // iPod
console.log(toy.getColor());  // black
var getName = toy.getName;
console.log(getName());       // iPod