through2-map

through2-map
============


This is a super thin wrapper around through2 that works like Array.prototype.map but for streams.

For when through2 is just too verbose :wink:

Note you will NOT be able to skip chunks. This is intended for modification only. If you want filter the stream content, use either through2 or through2-filter. This transform also does not have a flush function.

IMPORTANT: If you return null from your function, the stream will end there.

``js

var map = require("through2-map")

var truncate = map(function (chunk) {
return chunk.slice(0, 10)
})

// vs. with through2:
var truncate = through2(function (chunk, encoding, callback) {
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) {
// OMG don't actually use this
return 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) {
return (index % 2 == 0) ? chunk + "\n\n" : chunk
})

// vs. with through2:
var spaceout = through2(function (chunk, encoding, callback) {
if (this.index == undefined) this.index = 0
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-map")([options,] fn)
`

Create a stream.Transform instance that will call fn(chunk, index) on each stream segment.

- - -

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

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

- - -

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

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

- - -

`
require("through2-map").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