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    through2-map
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    3.0.0 • Public • Published

    through2-map

    NPM

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

    For when through2 is just too verbose 😉

    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.

     
    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

    Install

    npm i through2-map

    DownloadsWeekly Downloads

    131,088

    Version

    3.0.0

    License

    MIT

    Last publish

    Collaborators

    • bryce