"Wealthfront-style" Option Monad using ES6 Iterators

option.js

/*
 * A Wealthfront-style Option implementation in Javascript implementing ES6 iterables
 * Reference:
 *  http://eng.wealthfront.com/2010/05/better-option-for-java.html
 * 
 * This only runs in current versions of Firefox.
 * It's recommended you use the FF Scratchpad with the web console open to see logging results:
 *  https://developer.mozilla.org/en-US/docs/Tools/Scratchpad
 */

function Option(v) {
  this.v = v;
}
Option.prototype.__iterator__ = function(){
  return new OptionIterator(this);
};
Option.of = function (v) {
  return new Option(v);
}

function OptionIterator(option) {
  this.option = option;
  this.accessed = false;
}
OptionIterator.prototype.next = function() {
  if (this.accessed || this.option.v === null) {
    throw StopIteration;
  }
  this.accessed = true;
  return this.option.v;
}

var maybeThereButIsnt = Option.of(null);
var maybeThereAndIs = Option.of(20);

for(var value in maybeThereButIsnt) {
  console.log("I'm not here! " + value);
}

for(var value in maybeThereAndIs) {
  console.log("I'm here! " + value);
}

/*
 * Console Output:
 *
 * > "I'm here! 20"
 *
 */