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.

1
2var map = require("through2-map")
3
4var truncate = map(function (chunk) {
5  return chunk.slice(0, 10)
6})
7
8// vs. with through2:
9var truncate = through2(function (chunk, encoding, callback) {
10  this.push(chunk.slice(0, 10))
11  return callback()
12})
13
14// Then use your map:
15source.pipe(truncate).pipe(sink)
16
17// Additionally accepts `wantStrings` argument to convert buffers into strings
18var stripTags = map({wantStrings: true}, function (str) {
19  // OMG don't actually use this
20  return str.replace(/<.*?>/g, "")
21})
22
23// Works like `Array.prototype.map` meaning you can specify a function that
24// takes up to two* arguments: fn(chunk, index)
25var spaceout = map({wantStrings: true}, function (chunk, index) {
26  return (index % 2 == 0) ? chunk + "\n\n" : chunk
27})
28
29// vs. with through2:
30var spaceout = through2(function (chunk, encoding, callback) {
31  if (this.index == undefined) this.index = 0
32  var buf = (this.index++ % 2 == 0) ? Buffer.concat(chunk, new Buffer("\n\n")) : chunk
33  this.push(buf)
34  return callback()
35})
36

*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