StepSequencer without GUI with gamejs

main.js

var gamejs = require('gamejs');
var mixer = require('gamejs/mixer');
var stepsequencer = require('stepsequencer');

var FPS = 60;
var BPM = 100;

var extAudio = ".ogg";
// var extAudio = ".wav";


function main() {

   var display = gamejs.display.setMode([500, 350]);

   var font = new gamejs.font.Font('20px monospace');
   
   var sndKick  = new gamejs.mixer.Sound('data/kick1'+extAudio);
   var sndSnare = new gamejs.mixer.Sound('data/snare1'+extAudio);
   var sndHiHat = new gamejs.mixer.Sound('data/hihat1'+extAudio);
   var sndHiHat2 = new gamejs.mixer.Sound('data/hihat2'+extAudio);

   var seq = new stepsequencer.StepSequencer();
   
   seq.addAction(0, 0, sndKick);
   seq.addAction(0, 3, sndKick);
   seq.addAction(0, 9, sndKick);

   seq.addAction(1, 4, sndSnare);
   seq.addAction(1, 12, sndSnare);

   for (var i=0; i < 16; i++) {
   	 if (i%4==0) continue;
     seq.addAction(2, i, sndHiHat);
   }
   
   for (var i=0; i < 16; i+=4) {
     seq.addAction(2, i, sndHiHat2);
   }

   function seqUpdate () {
     seq.update();
   };

   /**
    * tick
    */
   function tick () {
      
      // event handling
      gamejs.event.get().forEach(function(event) {
         if (event.type === gamejs.event.KEY_DOWN) {
         		
         } else if (event.type === gamejs.event.MOUSE_MOTION) {
         
         }
      });

      // draw
      display.clear();
      display.blit(font.render(seq._step, '#ff0000'), [250, 50]);
   };
   gamejs.time.fpsCallback(tick, this, FPS);
   // FPS*60 = FPM, FPM/BPM
   // TODO bind to High Resolution Timer 
   gamejs.time.fpsCallback(seqUpdate, this, 6 );

};

gamejs.preload([
   'data/kick1.wav',
   'data/kick1.ogg',
   'data/kick1.wav',
   'data/snare1.ogg',
   'data/snare1.wav',
   'data/hihat1.ogg',
   'data/hihat1.wav',
   'data/hihat2.ogg',
   'data/hihat2.wav'
]);
gamejs.ready(main);

stepsequencer.js

var StepSequencer = exports.StepSequencer = function(bpm, fps) {
	
	this._bpm = bpm || 120;
	this._fps = fps || 60;
	this._tick = 0;
	this._step = 0;
	this._actions = {};
	this._stepCount = 16;
	this._layers = 0;

	this.addAction = function(layer, index, item) {
		if (typeof this._actions[layer] == 'undefined') {
			this._actions[layer] = {};
			this._layers++;
		}
		this._actions[layer][index] = item;
	};
	
	this.update = function() {
		for (var layer=0; layer < this._layers + 1; layer++) {
			if (typeof this._actions[layer] != 'undefined'
			&& typeof this._actions[layer][this._step] != 'undefined') {
				this._actions[layer][this._step].play();
			}
		}
		this._step++;
		if ((this._step % this._stepCount)==0) {
			this._step = 0;
		}

	};
	
	this.tick = function() {
		// tick is a FPS helper
		if (((this._tick / this._fps) * this._bpm) % this._stepCount ==0 ) {
			this.update();
		}
		this._tick++;
	};
	
};