(function(cmd, fire) {
  var keys = [];
  var l = cmd.length, CMD = cmd.join(',');
  $(document).on('keydown', function(event) {
    keys.push(event.which);
    if (keys.length < l) return true;
    if (keys.join(',') === CMD) fire();
    keys = [];
  });
})([38,38,40,40,37,39,37,39,66,65], function(){
  // ここにコナミコマンドのイベントを実装
});