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0.14.6 • Public • Published


Music21j: An Interactive Framework for Musical Analysis

Copyright ©2013-21, Michael Scott Asato Cuthbert, some rights reserved (BSD).

Music21j is a Javascript reinterpretation of the Music21 Python package, a toolkit for computer-aided musicology, now with intuitive HTML/Javascript interfaces. Some things music21j offers are:

  • The ability to visualize and hear changes in Streams quickly (using Vexflow and MIDI.js)
  • Connections (via Web Midi or JazzSoft plugin) to MIDI devices.
  • Music theory and analysis modules at the level of music21 ca. 2014
  • A repository of modules such as metronomes, keyboards, and automatic transcribers.

Though it does not have all the power of Music21 Python, music21j can help with a number of research problems in music history and theory. The introduction to the Python package will say more about it (it's better documented). The "namespaces" tab above will give introductions to some features of music21j. At this point we're focusing on documenting usage; developer docs will come later.

Music21j requires your users to have a relatively recent web browser -- the project targets browsers no more than two years old. Safari 9+, Chrome since 2015 (v.32+), Edge 14+, or Firefox since 2014 (v. 26+).
Internet Explorer 11+ is currently supported, though timing of playback can be a bit off, but support for it will be removed soon. Microsoft Edge is the only major desktop browser for which there is no support for MIDI devices.


This README appears in both the GitHub home page and the documentation home page; to make the following links work, go to the documentation page at .

Begin at the {@link music21} namespace (click the link or use the menu above), or start with a specific one such as {@link music21.note} or {@link} or a Class such as {@link music21.note.Note} or {@link}.

(Ignore "Modules" they're not useful and duplicate the namespace pages).


Install by downloading a copy of the music21 code to your own webserver.

% npm install music21j

If this line (npm install) doesn't work, download the latest version of node.js from

A guide to installing music21j on Windows would be appreciated.

The files in music21j are best viewed by running your own webserver (rather than using file:///... links). We've included a small script to start you up:

$ cd ~/git/music21j
$ grunt webpack
$ python

Then navigate to http://localhost:8000/testHTML/ for some demos.

To use music21j in your own page, place in a html page like this (this assumes that you're using the python server above).

<html lang="en">
<title>music21 test</title>
   <script src="/node_modules/music21j/releases/music21.debug.js">
   const n = new music21.note.Note('F#');
   const s = new;

or use it in your own Javascript/Typescript project:

$ npm install --save music21j
import * as music21 from 'music21j';

const n = new music21.note.Note('F#');
// etc.


0.14.6 beta


Music21j is released under the BSD 3-Clause License. Essentially you can do with it what you want so long as you leave in my copyright statements and do not represent that I endorse your product.

Or you can choose to use the GNU Lesser Public License if for some reason that suits your project better.


Thanks to the following packages (among others) for making music21j possible:

  • Vexflow - music notation in HTML5
  • midicube - audio processing of MIDI based on MIDI.js
  • Jazzsoft - plug-in for accessing MIDI in the browser in the absence of WebMIDI Api.
  • qUnit - testing framework
  • jsdoc - makes this documentation possible

The Python version of music21 was supported by grants from the Seaver Institute and the National Endowment for the Humanities and supported by the Music and Theater Arts section of MIT.

Dev Notes

Build and watch with

$ grunt

test with

$ grunt test

You might get an error that looks like this which you can currently ignore:

Access to XMLHttpRequest at 
from origin 'null' has been blocked by CORS policy

We hope to fix it later, but for now, we're not testing audio output.

for running tests one time without watch, you can use:

$ grunt test_no_watch

Publishing a new version

You'll need to be part of the npm dev team.

Two steps. First run:

$ grunt publish

which will update the version number and tries to build the docs via grunt jsdoc (currently failing).

The template is specified in jsdoc-template/jsdoc.conf.json

For a non-backwards compatible release, edit the minor version number manually here, in main.ts, and of course in package.json.

Then run:

$ npm publish

which will copy the current contents of build in releases and publish on npm.

Before publishing, every once in a while run (in the music21j directory)

$ node_modules/.bin/npm-check-updates

and if it looks like something to update, run

$ node_modules/.bin/npm-check-updates -u
$ npm install

These docs will be changing in preparation for v. 1.0 release.

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