nyan.js

var KeyBoard = function(){
  var keys = [];
  for (var i = 0, l= 64; i < l; i++ ){
    keys[i] = false;
  }
  this.keys = keys;
};

KeyBoard.prototype = {
  indexOf: function(keyCode, oct){
    var base;
    switch (keyCode) {
      case 'c':
        base = 0;
        break;
      case 'c#':
        base = 1;
        break;
      case 'd':
        base = 2;
        break;
      case 'd#':
        base = 3;
        break;
      case 'e':
        base = 4;
        break;
      case 'f':
        base = 5;
        break;
      case 'f#':
        base = 6;
        break;
      case 'g':
        base = 7;
        break;
      case 'g#':
        base = 8;
        break;
      case 'a':
        base = 9;
        break;
      case 'a#':
        base = 10;
        break;
      case 'b':
        base = 11;
        break;
    }
    var index = base + (11 * oct);
    return index;
  },

  push: function(keyCode, oct){
    this.keys[this.indexOf(keyCode, oct)] = true;
  },

  unpush: function(keyCode, oct){
    this.keys[this.indexOf(keyCode, oct)] = false;
  },

  asArray: function(){
    return this.keys;
  }
};

var keyBoard = new KeyBoard();
keyBoard.push('c', 0);
keyBoard.push('e', 0);
keyBoard.push('g', 0);
console.log(keyBoard.asArray());