generator.es5

function generator() {
  var i = 0;
  return {
    next: function() {
      i++;
      if (i >= 3) {
        return {done: true};
      } else {
        return {
          value: i,
          done: false
        };
      }
    }
  };
}

function fn() {
  var iterator = generator();
  iterator.next();
  iterator.next();
  return iterator.next().done;
}

assertEqual(fn(), true);
test(fn);