MidiPlayerJS is a JavaScript library which reads standard MIDI files and emits JSON events in real time. This player does not generate any audio, but by attaching a handler to the event emitter you can trigger any code you like which could play audio, control visualizations, feed into a MIDI interface, etc.

• Neopixel Music by robertvorthman @robertvorthman
• Autocomposer by RJ Salvador @rjsalvadorr
• Simple Browser Player by Garrett Grimm @grimmdude
• Orchestra by Daniel Alejandro Cast @lexcast

Using MidiWriterJS is pretty simple. Create a new player by instantiating MidiPlayer.Player with an event handler to be called for every MIDI event. Then you can load and play a MIDI file.

var MidiPlayer = require('midi-player-js');

// Initialize player and register event handler
var Player = new MidiPlayer.Player(function(event) {
	console.log(event);
});

// Load a MIDI file
Player.loadFile('./test.mid');
Player.play();

There are a handful of events on the Player object which you can subscribe to using the Player.on() method. Some events pass data as the first argument of the callback as described below:

Player.on('fileLoaded', function() {
    // Do something when file is loaded
});

Player.on('playing', function(currentTick) {
    // Do something while player is playing
    // (this is repeatedly triggered within the play loop)
});

Player.on('midiEvent', function(event) {
    // Do something when a MIDI event is fired.
    // (this is the same as passing a function to MidiPlayer.Player() when instantiating.
});

Player.on('endOfFile', function() {
    // Do something when end of the file has been reached.
});

Note that because of a common practice called "running status" many MIDI files may use Note on events with 0 velocity in place of Note off events.

http://grimmdude.com/MidiPlayerJS/docs/