virtualStream in node js

virtualStream

var fs = require('fs');
var stream = require('stream');
var util = require('util');


function virtualStream() {
  stream.Transform.call(this);
  this._readableState.objectMode = false;
  this._writableState.objectMode = true;
}
util.inherits(virtualStream, stream.Transform);
//
virtualStream.prototype._transform = function (obj, encoding, cb) {
  this.push(new Buffer(obj.toString().replace('replace this', 'replaced to that')));
//  this.push(JSON.stringify(obj));
  cb();
};


var rrs = fs.createReadStream(__dirname + '/shm.txt');
var ws = fs.createWriteStream(__dirname + '/s.txt');



rrs.pipe(new virtualStream()).pipe(ws);