JS动态设置倒数时间

<script type="text/javascript">
function run(){
var hiddenValue = document.getElementById("btn_HiddenValue");
var submitValue = document.getElementById("btn_Submit");
if(hiddenValue.value == 0)
{
   submitValue.value = "同意";
   submitValue.disabled = "";
   return false;
}
hiddenValue.value = hiddenValue.value * 1 - 1;
submitValue.value = "同意[" + hiddenValue.value + "]";
}
window.setInterval("run();", 1000);
</script>