function CountDown(){
     var count = 4 , tmID, infobox = document.getElementById("start"),
                 hit = Math.floor(Math.random()*10),
                 atari = document.querySelectorAll("div"),
                 res = document.getElementById("result");
     function countdown(){
      if(--count==0){
       res.innerHTML = "失敗";
       infobox.innerHTML ="時間切れだよ";
       atari[hit].removeEventListener("click", stopCountDown, false);
       } else {
           infobox.innerHTML = count + "秒前";
           tmID = setTimeout(countdown, 1000);
          }
     }
     function startCountDown(){
      tmID = setTimeout(countdown, 0);
      infobox.removeEventListener("click", startCountDown, false);
      atari[hit].addEventListener("click", stopCountDown, false);
     }
     function stopCountDown(){
      clearTimeout(tmID);
      res.innerHTML = "当たり!";
     }
     infobox.addEventListener("click", startCountDown, false);
    }
    document.addEventListener("DOMContentLoaded", CountDown, false);