希望javascript倒计时从刷新后的位置继续

我正在使用以下代码设计3小时的JavaScript倒计时

<div id="timer"></div>
<script type="text/javascript">
var count = 10800;
var counter = setInterval(timer, 1000); //1000 will  run it every 1 second

function timer() {
count = count - 1;
if (count == -1) {
    clearInterval(counter);
    return;
}

var seconds = count % 60;
var minutes = Math.floor(count / 60);
var hours = Math.floor(minutes / 60);
minutes %= 60;
hours %= 60;

document.getElementById("timer").innerHTML = hours +  "hours "  + minutes +  "minutes and "   + seconds +  "  seconds left to complete this transaction"; // watch for spelling
}
</script>

但是我这里唯一的问题是，每当刷新页面时，倒计时都会重新开始。我希望它从停止的地方继续。