function CountDown() {
var count = 30, tmID, infobox = document.getElementById("start"), 
hit = Math.floor(Math.random()*10+1), areas = document.querySelectorAll("div");
function countDown() {
  if (--count == "0") {
    infobox.innerHTML = "おわり";
   for (let i of areas) {
   	if (i.textContent == hit) {
	    i.removeEventListener("click", stopCountDown, false);
   	}
   }
  } else {
    infobox.innerHTML = count + "秒前";
    tmID = setTimeout(countDown, 1000);
  }
}
function startCountDown() {
  tmID = setTimeout(countDown, 1000);
  infobox.removeEventListener("click", startCountDown, false);
   for (let i of areas) {
   	if (i.textContent == hit) {
	    i.addEventListener("click", stopCountDown, false);
   	}
   }
}
function stopCountDown() {
  clearTimeout(tmID);
  infobox.innerHTML = "あたり";
  areas.removeEventListener("click", stopCountDown, false);
}
infobox.addEventListener("click", startCountDown, false);
}
document.addEventListener("DOMContentLoaded", CountDown, false);