How to use the asynciterator.TransformIterator.call function in asynciterator

function TurtleFragmentIterator(source, fragmentUrl) {
  if (!(this instanceof TurtleFragmentIterator))
    return new TurtleFragmentIterator(source, fragmentUrl);
  TransformIterator.call(this, source);
  this._fragmentUrl = fragmentUrl;

  // Expose an additional metadata stream
  this.metadataStream = new BufferedIterator();
  if (source && source.ended) return this.metadataStream._push(null);
  // When a metadata listener is added, drain the source to read metadata
  var self = this;
  this.metadataStream.on('newListener', function metadataListenerAdded(event) {
    if (event === 'data' || event === 'end') {
      this.removeListener('newListener', metadataListenerAdded);
      self.maxBufferSize = Infinity;
    }
  });

  // Convert Turtle into triples using the N3 parser
  this._parser = new N3.Parser({ documentURI: fragmentUrl });

function SortIterator(source, sort, options) {
  if (!(this instanceof SortIterator))
    return new SortIterator(source, sort, options);
  // Shift arguments if `sort` is omitted
  if (typeof sort !== 'function')
    options = sort, sort = null;
  TransformIterator.call(this, source, options);

  // The `window` parameter indicates the length of the sliding window to apply sorting
  var window = options && options.window;
  this._windowLength = isFinite(window) && window > 0 ? ~~window : Infinity;
  this._sort = sort || defaultSort;
  this._sorted = [];
}
TransformIterator.subclass(SortIterator);

function SparqlResultWriter(source) {
  TransformIterator.call(this, source);
  this._empty = true;
  this._variables = source.getProperty('variables') || [];
}
TransformIterator.subclass(SparqlResultWriter);