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Turn a writeable and readable stream into a single streams2 duplex stream.

Similar to duplexer2 except it supports both streams2 and streams1 as input and it allows you to set the readable and writable part asynchronously using setReadable(stream) and setWritable(stream)

npm install duplexify

build status


Use duplexify(writable, readable, streamOptions) (or duplexify.obj(writable, readable) to create an object stream)

var duplexify = require('duplexify')

// turn writableStream and readableStream into a single duplex stream
var dup = duplexify(writableStream, readableStream)

dup.write('hello world') // will write to writableStream
dup.on('data', function(data) {
  // will read from readableStream

You can also set the readable and writable parts asynchronously

var dup = duplexify()

dup.write('hello world') // write will buffer until the writable
                         // part has been set

// wait a bit ...

// maybe wait some more?

If you call setReadable or setWritable multiple times it will unregister the previous readable/writable stream. To disable the readable or writable part call setReadable or setWritable with null.

If the readable or writable streams emits an error or close it will destroy both streams and bubble up the event. You can also explicitly destroy the streams by calling dup.destroy(). The destroy method optionally takes an error object as argument, in which case the error is emitted as part of the error event.

dup.on('error', function(err) {
  console.log('readable or writable emitted an error - close will follow')

dup.on('close', function() {
  console.log('the duplex stream is destroyed')

dup.destroy() // calls destroy on the readable and writable part (if present)

HTTP request example

Turn a node core http request into a duplex stream is as easy as

var duplexify = require('duplexify')
var http = require('http')

var request = function(opts) {
  var req = http.request(opts)
  var dup = duplexify(req)
  req.on('response', function(res) {
  return dup

var req = request({
  method: 'GET',
  host: 'www.google.com',
  port: 80




duplexify is part of the mississippi stream utility collection which includes more useful stream modules similar to this one.