Emulating ES.next private names in spidermonkey

private-names.js

/*jshint asi:true */
!(function(getOwnNames, getKeys, nil) {
  function ignore() {}
  function nonPrivate(name) { return name[0] !== '\\' }

  Object.defineProperties(Object, {
    getOwnPropertyNames: { value: (function(object) {
      return getOwnNames(object).filter(nonPrivate)
    }).bind(null) },
    keys: { value: (function(object) {
      return getKeys(object).filter(nonPrivate)
    }).bind(null) }
  })

  Object.defineProperty(Object.prototype, '__iterator__', {
    value: function iterator(names) {
      let iteratee = Object.create(this, { '__iterator__': { value: nil } })
      for (let name in iteratee) {
        if (nonPrivate(name))
          yield names ? name : iteratee[name]
      }
    }
  })

})(Object.getOwnPropertyNames, Object.keys)

function Name() {
  return Object.create(Name.prototype, {
    toString: {
      value: String.bind(null, '\\' + Math.round(Math.random() * 1000000000000))
    }
  })
}

function props(object) {
  var result = []
  for (let key in object) result.push(key)
  return result
}

var bar = new Name()
var a = { foo: 'foo!' }
a[bar] = 'bar'

Object.keys(a)
Object.getOwnPropertyNames(a)
props(a)

var b = Object.create(a)
Object.keys(b)
Object.getOwnPropertyNames(b)
props(b)

Only issue with this approach is that if one creates Object.create(yourObject, { __iterator__: { value: undefined } }) he will be able to gain access to all private names and properties.