code: function Iterator(db, options) {
    this.db = db;
    this.options = new IteratorOptions(options);
    this.iter = null;
    this.ended = false;
    this.total = 0;
    this.init();
  }
docs: Iterator
  @constructor
  @ignore
  @private
  @param {RBT} db
  @param {Object?} options