js实现倒计时

<!-- 倒计时 -->
<span id="times1">120：00</span>

<script type="text/javascript">
var m = 119;
var s = 59;
function times(){
if(s == -1){
m--;
s = 59;
}
$("#times1").text(m + "：" + (s < 10 ? "0" + s : s));
s--;
if(m == 0 && s == -1){
alert("时间到了！");
clearInterval(iCount);
return;
}
}
var iCount = setInterval("times()",1000);
</script>