An async version of through2-map -- async for streams

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201.1.08 years ago8 years agoMinified + gzip package size for through2-asyncmap in KB


An async-only version of through2-map
var map = require("through2-asyncmap")

var truncate = map(function (chunk, callback) {
  setImmediate(function () {
    callback(null, chunk.slice(0, 10))

// vs. with through2:
var truncate = through2(function (chunk, encoding, callback) {
  setImmediate(function () {
    this.push(chunk.slice(0, 10))
    return callback()

// Then use your map:

// Additionally accepts `wantStrings` argument to convert buffers into strings
var stripTags = map({wantStrings: true}, function (str, next) {
  // OMG don't actually use this
  setImmediate(function () {next(null, str.replace(/<.*?>/g, ""))}

// Works like `` meaning you can specify a function that
// takes up to two* arguments: fn(chunk, index)
var spaceout = map({wantStrings: true}, function (chunk, index, callback) {
  setImmediate(functio () {
    callback(null, (index % 2 == 0) ? chunk + "\n\n" : chunk)

// vs. with through2:
var spaceout = through2(function (chunk, encoding, callback) {
  if (this.index == undefined) {
    this.index = 0
  setImmediate(function () {
    var buf = (this.index++ % 2 == 0) ? Buffer.concat(chunk, new Buffer("\n\n")) : chunk
    return callback()

Differences from Cannot insert null elements into the stream without aborting. No third array callback argument. That would require realizing the entire stream, which is generally counter-productive to stream operations. doesn't modify the source Array, which is somewhat nonsensical when applied to streams.


require("through2-asyncmap")([options,] fn)

Create a stream.Transform instance that will call fn(chunk, [index,] callback) on each stream segment.
callback is expected to return two arguments: callback(error, replacementChunk) and will replace the provided chunk with replacementChunk
If error is true, it will emit that error on the stream.

var Tx = require("through2-asyncmap").ctor([options,] fn)

Create a reusable stream.Transform TYPE that can be called via new Tx or Tx() to create an instance.

require("through2-asyncmap").obj([options,] fn)

Create a through2-asyncmap instance that defaults to objectMode: true.

require("through2-asyncmap").objCtor([options,] fn)

Just like ctor, but with objectMode: true defaulting to true.


wantStrings: Automatically call chunk.toString() for the super lazy. all other through2 options