code: function Iterator(options, fn) {
    if (typeof options === 'function') {
      fn = options;
      options = {};
    }
    if (typeof fn !== 'function') {
      throw new TypeError('Iterator expects `fn` to be a function.');
    }
    this.options = options || {};
    this.fn = fn;
  }
docs: Create a new instance of `Iterator`
  
  ```js
  var iterator = new Iterator();
  ```
  @api public