through2-asyncmap

through2-asyncmap
============


An async-only version of through2-map

``js

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:
source.pipe(truncate).pipe(sink)

// 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 Array.prototype.map 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
this.push(buf)
return callback()
})
})

`

*Differences from Array.prototype.map:
* 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.
* Array.prototype.map doesn't modify the source Array, which is somewhat nonsensical when applied to streams.

API
---

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.

Options
-------

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

LICENSE
=======

MIT