i want to open a div after countdown timer stops

I am building an aptitude test with a timer. i want to show a div of time out on countdown finish. and is it possible to show a **Lean Modal Popup ** box on countdown finish. Please help!!!. Heres the code

Javascript

<script language="JavaScript" type="text/javascript">

function CountDownTimer(duration, granularity) {
  this.duration = duration;
  this.granularity = granularity || 1000;
  this.tickFtns = [];
  this.running = false;
}

CountDownTimer.prototype.start = function() {
  if (this.running) {
    return;
  }
  this.running = true;
  var start = Date.now(),
      that = this,
      diff, obj;

  (function timer() {
    diff = that.duration - (((Date.now() - start) / 1000) | 0);

    if (diff > 0) {
      setTimeout(timer, that.granularity);
    } else {
      diff = 0;
      that.running = false;
    }

    obj = CountDownTimer.parse(diff);
    that.tickFtns.forEach(function(ftn) {
      ftn.call(this, obj.minutes, obj.seconds);
    }, that);
  }());
};

CountDownTimer.prototype.onTick = function(ftn) {
  if (typeof ftn === 'function') {
    this.tickFtns.push(ftn);
  }
  return this;
};

CountDownTimer.prototype.expired = function() {
  return !this.running;
};

CountDownTimer.parse = function(seconds) {
  return {
    'minutes': (seconds / 60) | 0,
    'seconds': (seconds % 60) | 0
  };
};


window.onload = function () {
    var display = document.querySelector('#time'),
        timer = new CountDownTimer(5),
        timeObj = CountDownTimer.parse(5);

    format(timeObj.minutes, timeObj.seconds);

    timer.onTick(format);

    document.querySelector('button').addEventListener('click', function () {
        timer.start();
    });

    function format(minutes, seconds) {
        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;
        display.textContent = minutes + ':' + seconds;
}

if(display.textContent == 0){


            document.querySelector("#div1").style.display="block";





}



};



</script>

Html

<button>Start Count Down</button>
    <div>Registration closes in <span id="time"></span> minutes!</div>

div to show

<div id="div1" style="display:none;" ><p>Hello</p></div>

Ok, so the thing is, you have this piece of javascript code:

    window.onload = function () {
    var display = document.querySelector('#time'),
        timer = new CountDownTimer(5),
        timeObj = CountDownTimer.parse(5);

    format(timeObj.minutes, timeObj.seconds);

    timer.onTick(format);

    document.querySelector('button').addEventListener('click', function () {
        timer.start();
    });

    function format(minutes, seconds) {
        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;
        display.textContent = minutes + ':' + seconds;
}

if(display.textContent == 0){


            document.querySelector("#div1").style.display="block";





}

At the bottom, you have an "if" statement.

Just move that if statement into the "format" function as follow:

    window.onload = function () {
        var display = document.querySelector('#time'),
            timer = new CountDownTimer(5),
            timeObj = CountDownTimer.parse(5);

        format(timeObj.minutes, timeObj.seconds);

        timer.onTick(format);

        document.querySelector('button').addEventListener('click', function () {
            timer.start();
        });



 function format(minutes, seconds) {
        minutes = minutes < 10 ? "0" + minutes : minutes;
        seconds = seconds < 10 ? "0" + seconds : seconds;
        display.textContent = minutes + ':' + seconds;

        console.log(display.textContent);

        if(display.textContent == "00:00") {
            document.querySelector("#div1").style.display="block";
        }
    }
};

Your code, the way it currently is, is not performing the check on every tick.

Also, you are not checking against "0". The value should be "00:00"

Of course, you can move the check to show the div into the tick event, but that is totally up to you.