code: function ReadableSerialOrdered(list, iterator, sortMethod, callback)
  {
    if (!(this instanceof ReadableSerialOrdered))
    {
      return new ReadableSerialOrdered(list, iterator, sortMethod, callback);
    }
  
    // turn on object mode
    ReadableSerialOrdered.super_.call(this, {objectMode: true});
  
    this._start(serialOrdered, list, iterator, sortMethod, callback);
  }
docs: Streaming wrapper to `asynckit.serialOrdered`
  
  @param   {array|object} list - array or object (named list) to iterate over
  @param   {function} iterator - iterator to run
  @param   {function} sortMethod - custom sort function
  @param   {function} callback - invoked when all elements processed
  @returns {stream.Readable#}