iterator.js

function Words(str) {
  this._str = str;
}

Words.prototype[Symbol.iterator] = function() {
  var re = /\S+/g;
  var str = this._str;

  return {
    next: function() {
      var match = re.exec(str);
      if (match) {
        return {value: match[0], done: false};
      }
      return {value: undefined, done: true};
    }
  }
};