<script language="JavaScript">
var da = 120;//倒计时时间（秒）

function sj()
{
  var min, sec, str;
  min = Math.floor(da/60);
  sec = Math.floor(da%60);
  if(isNaN(min))
    return "0:00";
  str = min.toString()+":";
  if(sec>9)
    str += sec.toString();
  else
    str += "0"+sec.toString();
  dao.innerText = str;
  if(da<=0)
  {
    clearInterval(st);
    alert("时间到，表单自动提交！");
    document.formname.submit();
  }
  da--;
}
sj();
var st = setInterval("sj()",1000);
</script>