contra.js

var Contra = (function() {

  var a = 65,
      b = 66,
      left = 37,
      up = 38,
      right = 39, 
      down = 40,
      handlers = [],
      pattern = [up, up, down, down, left, right, left, right, b, a],
      position = 0;

  function check(evt) {
    if (pattern[position] === evt.keyCode) {
      position++;
    } else {
      position = 0;
    }

    if (position === pattern.length) {
      win();
      position = 0;
    }
  }

  function win() {
    var body = document.getElementsByTagName('body')[0];
    body.className = body.className + ' contra';

    for(var i = 0, l = handlers.length; i<l; i++) {
      handlers[i].call();
    }
  }

    if (document.addEventListener) {
      document.addEventListener('keyup', check);
    } else if(document.attachEvent) {
      document.attachEvent('onkeypress', check);
	}

  return {
	addHandler: function(handler) {
    	handlers.push(handler);
  	}
  }

}());