To create your own writable stream, you have three possibilities.

Create your own class

For this you'll need 1) to extend the Writable class 2) to call the Writable constructor in your own constructor 3) define a _write() method in the prototype of your stream object.

Here's an example :

var stream = require('stream');var util = require('util');function EchoStream () { // step 2  stream.Writable.call(this);};util.inherits(EchoStream, stream.Writable); // step 1EchoStream.prototype._write = function (chunk, encoding, done) { // step 3  console.log(chunk.toString());  done();}var myStream = new EchoStream(); // instanciate your brand new streamprocess.stdin.pipe(myStream);

Extend an empty Writable object

Instead of defining a new object type, you can instanciate an empty Writable object and implement the _write() method:

var stream = require('stream');var echoStream = new stream.Writable();echoStream._write = function (chunk, encoding, done) {  console.log(chunk.toString());  done();};process.stdin.pipe(echoStream);

Use the Simplified Constructor API

If you're using io.js, you can use the simplified constructor API:

var writable = new stream.Writable({  write: function(chunk, encoding, next) {    console.log(chunk.toString());    next();  }});

Use an ES6 class in Node 4+

class EchoStream extends stream.Writable {  _write(chunk, enc, next) {    console.log(chunk.toString());    next();  }}

Actually to create a writeable stream is quite simple.Here's is the example:

var fs = require('fs');var Stream = require('stream');var ws = new Stream;ws.writable = true;ws.bytes = 0;ws.write = function(buf) {   ws.bytes += buf.length;}ws.end = function(buf) {   if(arguments.length) ws.write(buf);   ws.writable = false;   console.log('bytes length: ' + ws.bytes);}fs.createReadStream('file path').pipe(ws);

Also if you want to create your own class, @Paul give a good answer.