倒计时防刷新的实现

<script type="text/javascript">
  var maxtime;
  if(window.name == ''){ 
    maxtime = 60 * 60;
  }else{
    maxtime = window.name;
  }

  function CountDown(){
    if(maxtime >= 0){
      minutes = Math.floor(maxtime/60);
      seconds = Math.floor(maxtime%60);
      msg = "距离结束还有" + minutes + "分" + seconds + "秒";
      document.all["timer"].innerHTML = msg;
      if(maxtime == 5 * 60) alert('注意，还有5分钟!');
      --maxtime;
      window.name = maxtime; 
    }
    else{
      clearInterval(timer);
      alert("时间到，结束!");
    }
  }
  timer = setInterval("CountDown()", 1000);
</script>
<div id="timer" style="color:red"></div>