EventStream is like functional programming meets IO
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Streams are nodes best and most misunderstood idea, and EventStream is a toolkit to make creating and working with streams easy.

Normally, streams are only used of IO,
but in event stream we send all kinds of objects down the pipe.
If your application's input and output are streams,
shouldn't the throughput be a stream too?

The EventStream functions resemble the array functions,
because Streams are like Arrays, but laid out in time, rather than in memory.

All the event-stream functions return instances of Stream.

Stream API docs:

NOTE: I shall use the term "through stream" to refer to a stream that is writable and readable.

###simple example:


if(!module.parent) {
  var es = require('event-stream')
  es.pipeline(                         //connect streams together with `pipe`
    process.openStdin(),              //open stdin
    es.split(),                       //split stream to break on newlines (data, callback) {//turn this async function into a stream
        , inspect(JSON.parse(data)))  //render it nicely
    process.stdout                    // pipe it to stdout !

run it ...

curl -sS | node pretty.js

node Stream documentation

through (write?, end?)

Reemits data synchronously. Easy way to create syncronous through streams. Pass in an optional write and end methods. They will be called in the context of the stream. Use this.pause() and this.resume() to manage flow. Check this.paused to see current flow state. (write always returns !this.paused)

this function is the basis for most of the syncronous streams in event-stream.

es.through(function write(data) {
    this.emit('data', data)
  function end () { //optional

##map (asyncFunction)

Create a through stream from an asyncronous function.

var es = require('event-stream') (data, callback) {
  //transform data
  // ...
  callback(null, data)

Each map MUST call the callback. It may callback with data, with an error or with no arguments,

  • callback() drop this data.
    this makes the map work like filter,
    note:callback(null,null) is not the same, and will emit null

  • callback(null, newData) turn data into newData

  • callback(error) emit an error for this item.

Note: if a callback is not called, map will think that it is still being processed,
every call must be answered or the stream will not know when to end.

Also, if the callback is called more than once, every call but the first will be ignored.

mapSync (syncFunction)

Same as map, but the callback is called synchronously. Based on es.through

split (matcher)

Break up a stream and reassemble it so that each line is a chunk. matcher may be a String, or a RegExp

Example, read every line in a file ...

    fs.createReadStream(file, {flags: 'r'}),
    es.split(), (line, cb) {
       //do something with the line 
       cb(null, line)

split takes the same arguments as string.split except it defaults to '\n' instead of ',', and the optional limit paremeter is ignored. String#split

join (seperator)

create a through stream that emits seperator between each chunk, just like Array#join.

(for legacy reasons, if you pass a callback instead of a string, join is a synonym for es.wait)

replace (from, to)

Replace all occurences of from with to. from may be a String or a RegExp.
Works just like string.split(from).join(to), but streaming.


Convienience function for parsing JSON chunks. For newline seperated JSON, use with es.split

  .pipe(es.split()) //defaults to lines.


convert javascript objects into lines of text. The text will have whitespace escaped and have a \n appended, so it will be compatible with es.parse


##readable (asyncFunction)

create a readable stream (that respects pause) from an async function.
while the stream is not paused,
the function will be polled with (count, callback),
and this will be the readable stream.

es.readable(function (count, callback) {
    return this.emit('end')
  this.emit('data', data) //use this way to emit multiple chunks per call.
  callback() // you MUST always call the callback eventually.
             // the function will not be called again until you do this.

you can also pass the data and the error to the callback.
you may only call the callback once.
calling the same callback more than once will have no effect.

##readArray (array)

Create a readable stream from an Array.

Just emit each item as a data event, respecting pause and resume.

  var es = require('event-stream')
    , reader = es.readArray([1,2,3])


writeArray (callback)

create a writeable stream from a callback,
all data events are stored in an array, which is passed to the callback when the stream ends.

  var es = require('event-stream')
    , reader = es.readArray([1, 2, 3])
    , writer = es.writeArray(function (err, array){
      //array deepEqual [1, 2, 3]


pipeline (stream1,...,streamN)

Turn a pipeline into a single stream. pipeline returns a stream that writes to the first stream and reads from the last stream.

Listening for 'error' will recieve errors from all streams inside the pipe.

connect is an alias for pipeline.

  es.pipeline(                         //connect streams together with `pipe`
    process.openStdin(),              //open stdin
    es.split(),                       //split stream to break on newlines (data, callback) {//turn this async function into a stream
        , inspect(JSON.parse(data)))  //render it nicely
    process.stdout                    // pipe it to stdout !

gate (isShut=true)

If the gate is shut, buffer the stream.
All calls to write will return false (pause upstream),
and end will not be sent downstream.

If the gate is open, let the stream through.

Named shut instead of close, because close is already kinda meaningful with streams.

Gate is useful for holding off processing a stream until some resource (i.e. a database, or network connection) is ready.

  var gate = es.gate() //allow the gate to stream
  gate.close() //buffer the stream, also do not allow 'end' 

duplex (writeStream, readStream)

Takes a writable stream and a readable stream and makes them appear as a readable writable stream.

It is assumed that the two streams are connected to each other in some way.

(This is used by pipeline and child.)

  var grep = cp.exec('grep Stream')

  es.duplex(grep.stdin, grep.stdout)

child (child_process)

Create a through stream from a child process ...

  var cp = require('child_process')

  es.child(cp.exec('grep Stream')) // a through stream

wait (callback)

waits for stream to emit 'end'. joins chunks of a stream into a single string. takes an optional callback, which will be passed the complete string when it receives the 'end' event.

also, emits a simgle 'data' event.

readStream.pipe(es.join(function (err, text) {
  // have complete text here.

pipeable (streamCreatorFunction,...)

The arguments to pipable must be functions that return
instances of Stream or async functions.
(If a function is returned, it will be turned into a Stream

Here is the first example rewritten to use pipeable.

var inspect = require('util').inspect

  require('event-stream').pipeable(function () {
    return function (data, callback) {
      try {
        data = JSON.parse(data)
      } catch (err) {}              //pass non JSON straight through!
      callback(null, inspect(data))
curl -sS | node pipeable_pretty.js

## or, turn the pipe into a server!

node pipeable_pretty.js --port 4646

curl -sS | curl -sSNT- localhost:4646

compatible modules:

almost compatible modules: (1+ these issues)