reverting defaults

settings.js

var settings = Object.create({
  _defaults: {},
  _values: {},
  setDefault: function (key, value) {
    this._values[key] = this[key]
    this._defaults[key] = value
    Object.defineProperty(this, key, {
      get: function () {
        var undef = typeof this._values[key] === 'undefined'
        return undef ? this._defaults[key] : this._values[key]
      },
      set: function (value) {
        this._values[key] = value
      }
    });
  }
});

module.exports = {
  create: function () {
    return Object.create(settings)
  }
}

///

var obj = settings.create()
obj.hello // obj === undefined
obj.hello = 5 // obj === 5
obj.setDefault('hello', 1); // obj === 5
obj.hello = undefined // obj === 1
obj.hello = null // obj === null