How to use the readable-stream/passthrough.call function in readable-stream

function Writable(fn, options) {
  if (!(this instanceof Writable))
    return new Writable(fn, options);

  PassThrough.call(this, options);

  beforeFirstCall(this, '_write', function() {
    var destination = fn.call(this, options);
    var emit = this.emit.bind(this, 'error');
    destination.on('error', emit);
    this.pipe(destination);
  });

  this.emit('writable');
}

function Writable(fn, options) {
  if (!(this instanceof Writable))
    return new Writable(fn, options);

  PassThrough.call(this, options);

  beforeFirstCall(this, '_write', function() {
    var destination = fn.call(this, options);
    var emit = this.emit.bind(this, 'error');
    destination.on('error', emit);
    this.pipe(destination);
  });

  this.emit('writable');
}

function Readable(fn, options) {
  if (!(this instanceof Readable))
    return new Readable(fn, options);

  PassThrough.call(this, options);

  beforeFirstCall(this, '_read', function() {
    var source = fn.call(this, options);
    var emit = this.emit.bind(this, 'error');
    source.on('error', emit);
    source.pipe(this);
  });

  this.emit('readable');
}

function Readable(fn, options) {
  if (!(this instanceof Readable))
    return new Readable(fn, options);

  PassThrough.call(this, options);

  beforeFirstCall(this, '_read', function() {
    var source = fn.call(this, options);
    var emit = this.emit.bind(this, 'error');
    source.on('error', emit);
    source.pipe(this);
  });

  this.emit('readable');
}

function PullStream(opts) {
  var self = this;
  this.opts = opts || {};
  PassThrough.call(this, opts);
  this.once('finish', function() {
    self._writesFinished = true;
    if (self._flushed) {
      self._finish();
    }
  });
  this.on('readable', function() {
    self._process();
  });
}
inherits(PullStream, PassThrough);

function Entry () {
  PassThrough.call(this);
  this.props = {};
}