3.9.3 • Public • Published


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A REPL where music is simply streams of input in node. Uses the awesome soundfonts of midi-js-soundfonts. Supports optional MIDI input.

Install via

npm install -g node-keyboard

Note: Installing node-keyboard will clone a soundfont library during install, resulting in an 800MB download.

Run via



Inside the REPL, the examples in the example folder are loaded as getters with the prefix example_. E.g. example_01_scales.chromatic({ key: 'b', ms: 100 })

Streaming Functionality tl;dr


Pipe the midiIn stream to a number of writable outputs. (To function, your MIDI device must be on when node starts.)

toAudio will play the notes


toRepl will output the notes in the REPL


toPiano will draw the piano for each note played


toLogger will console log the note (pipe after toAudio to see more information about the played note)


Or pipe them through each other midiIn.pipe(toPiano).pipe(toAudio)

And remove from MIDI input via midiIn.unpipe() (or CTRL+C)


Create a Stream

Create an [infinite] stream of notes from an array using from (supports notes as variables).

from(c, e, g).pipe(toAudio) // Hit CTRL+C (SIGINT) to unpipe immediately

Note: supports all notes A0 to Cs8/Db8 (Cs8 is the syntax-friendly version of 'C#8')


Use delay(...args) to return a transform stream that will emit after the given delays (where the delays are cycled)

from(c1, g1, c2, g2, c3, g3).pipe(delay(250, 250, 500)).pipe(toAudio)

With Instrument

Use on(instrument) to return a transform stream that will ensure the given instrument is used.


Note: Breaking via CTRL+C will stop the stream by unpiping everything

Functionality (sans streams)

Functionality, without the streams.


  • instruments list all instruments available
  • scales list all scales supported

Side effects

  • play(note) plays a note. Eg.
  • piano(note) draws the piano playing that note Eg.
[c,e,g].forEach((note, i) => setTimeout(() => piano(note), 400 * i))
  • log(note) logs the note to stdout. (Includes the instrument if chained after play) Eg.


  • chord(name) projects a chord name out to an array of notes. Eg.
// [ 'c4', 'eb4', 'g4', 'bb4', 'd5' ]
  • scale(note, name) projects a note through the named scale Eg.
scale('a', 'flamenco')
// [ 'a5', 'bb5', 'c#6', 'd6', 'e6', 'f6', 'g#6' ]
  • sequence(note, ...semitones) projects a note through the given semitone sequence Eg.
sequence(c, 2, 1, 2, 2, 1, 2, 2) // c minor scale
// [ 'c3', 'd3', 'eb3', 'f3', 'g3', 'g#3', 'a#3', 'c4' ]


  • instrument([name]]) returns mapping function to play on instrument. If no parameter provided it chooses a random instrument. Eg.:
  • interval(...intervals) returns mapping function to project intervals. Eg.
[c,e,g].map(interval('P1','P5')).reduce((acc, cur) => acc.concat(cur), [])
// [ 'c3', 'g3', 'e3', 'b3', 'g3', 'd4' ]
  • only(...numbers) returns filter predicate to filter out to required interval positions. Eg.
scale(c, 'major').filter(only(1,3,5,7)).map(play) // Cmaj7


Known Issues

  • Reusing a stream and repiping it through transformers E.g.
let guitar = from(c,e,g).pipe(on('guitar')).pipe(delay(200))
guitar.pipe(toAudio) // works
guitar.pipe(on()).pipe(toAudio) // works first time only
guitar.pipe(on()).pipe(toAudio) // won't play the guitar stream's final on() is still piped to the previous on()

More info

I spoke on node-keyboard at EmpireNode in November 2016 image


  • (see commit log for earlier releases)
  • 2.5.0 Support for switching instruments
  • 2.5.5 Adding every
  • 2.6.0 Persistent history for the REPL
    • 2.6.1 Adding eslint and ensuring play returns input
  • 2.7.0 Support for MIDI input
  • 2.8.0 Support for notes as first-class objects (Symbol-like)
  • 2.9.0 Support for midi streams: midiIn, toRepl, toAudio and toPiano
  • 3.0.0 Upgraded to stream-first, all stream variables are now factory functions (to reuse). Support for fromArray. Deprecated older array functionality.
  • 3.1.0 Renamed fromArray to from, allow from to continue forever, limited withDelay to have a highWaterMark of 1 and play first immediately, brought in SIGINT support to unpipe streams when CTRL+C pressed
  • 3.2.0 Renamed withDelay to delay. Added toLogger. Added on to play instruments.
  • 3.3.0 Added base functions chord(), scale, functors instrument() anf interval(), and properties instruments and scales. Many bug fixes.
  • 3.4.0 Migrated to using getters for writable streams for brevity
  • 3.5.0 Support for only()
  • 3.6.0 Subscription removal on SIGINT for Rx, support for piano function, support for runInThisContext, and stream getter bugfix
  • 3.7.0 Support for log function, removal of runInThisContext (not necessary)
  • 3.8.0 Errors no longer thrown, just shown. Support for examples
  • 3.9.0 Removed Rx support and turned it into a plugin


  1. When no octave is provided (e.g. play(a)) then 3rd octave (a3 220Hz) (starting at c3 on an 8-octave piano) is the default.

  2. a0, bb0 (a#0) and b0 are the only notes below c1

  3. Sharp can be denoated by s when not surrounding note by strings (i.e. as4 ==== 'a#4'). Double-sharp is denoted with x as in ax3 (enharmonically b3). Double-flat is denoted with bb as in bbb3 (enharmonically a3)


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