how to add timer to quiz in javascript code example

Example 1: add countdown timer to javascript quiz

var count = 15;
var interval = setInterval(function(){
  document.getElementById('count').innerHTML=count;
  count--;
  if (count === 0){
    clearInterval(interval);
    document.getElementById('count').innerHTML='Done';
    // or...
    alert("You're out of time!");
  }
}, 1000);

Example 2: adding a timer in a quiz game

var sec = 15;
var time = setInterval(myTimer, 1000);

function myTimer() {
    document.getElementById('timer').innerHTML = sec + "sec left";
    sec--;
    if (sec == -1) {
        clearInterval(time);
        alert("Time out!! :(");
    }
}