How to make count down timer universal

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C#

ASP.NET

Javascript

timer

i have a countdown timer,which has the span of 15 minutes once it end a new countdown of 15 minute will start.
the problem is that when ever i refresh page it also get refreshed.so kindly tell me how to make it universal.

What I have tried:

<script type = "text/javascript">

var timeInSecs;
var ticker;

function startTimer(secs) {
timeInSecs = parseInt(secs);
ticker = setInterval("tick()", 1000);
}

function tick() {
var secs = timeInSecs;
if (secs > 0) {
timeInSecs--;
}
else {
clearInterval(ticker);
startTimer(900); // start again
}

var hours = Math.floor(secs / 3600);
secs %= 3600;
var mins = Math.floor(secs / 60);
secs %= 60;
var pretty = ((hours < 10) ? "0" : "") + hours + ":" + ((mins < 10) ? "0" : "") + mins + ":" + ((secs < 10) ? "0" : "") + secs;
document.getElementById("countdown").innerHTML = pretty;
}

startTimer(900); // 15 minutes in seconds

</script>