writable stream that concatenates strings or binary data and calls a callback with the result


Writable stream that concatenates strings or binary data and calls a callback with the result. Not a transform stream -- more of a stream sink.

var fs = require('fs')
var concat = require('concat-stream')
var readStream = fs.createReadStream('cat.png')
var concatStream = concat(gotPicture)
readStream.on('error', handleError)
function gotPicture(imageBuffer) {
  // imageBuffer is all of `cat.png` as a node.js Buffer 
function handleError(err) {
  // handle your error appropriately here, e.g.: 
  console.error(err) // print the error to STDERR 
  process.exit(1) // exit program with non-zero exit code 
var write = concat(function(data) {})
// data will be [1,2,3,4,5,6] in the above callback 
var write = concat(function(data) {})
var a = new Uint8Array(3)
a[0] = 97; a[1] = 98; a[2] = 99

See test/ for more examples


var concat = require('concat-stream')

Return a writable stream that will fire cb(data) with all of the data that was written to the stream. Data can be written to writable as strings, Buffers, arrays of byte integers, and Uint8Arrays.

By default concat-stream will give you back the same data type as the type of the first buffer written to the stream. Use opts.encoding to set what format data should be returned as, e.g. if you if you don't want to rely on the built-in type checking or for some other reason.

  • string - get a string
  • buffer - get back a Buffer
  • array - get an array of byte integers
  • uint8array, u8, uint8 - get back a Uint8Array
  • object, get back an array of Objects

If you don't specify an encoding, and the types can't be inferred (e.g. you write things that aren't int he list above), it will try to convert concat them into a Buffer.

error handling

concat-stream does not handle errors for you, so you must handle errors on whatever streams you pipe into concat-stream. This is a general rule when programming with node.js streams: always handle errors on each and every stream. Since concat-stream is not itself a stream it does not emit errors.