页面倒计时
html：

<div class="timer">
<strong id="minute">0分</strong>
<strong id="second">0秒</strong>
</div>

Jquery：

 //计时器
        var intDiff = parseInt(1800);//倒计时总秒数量
        function timer(intDiff) {
            window.setInterval(function () {
                var minute = 0,
                    second = 0;//时间默认值        
                if (intDiff > 0) {
                    minute = Math.floor(intDiff / 60);
                    second = Math.floor(intDiff) - (minute * 60);
                }
                if (minute <= 9) minute = '0' + minute;
                if (second <= 9) second = '0' + second;
                $('#minute').html('<s></s>' + minute + '分');
                $('#second').html('<s></s>' + second + '秒');
                intDiff--;
                if (intDiff <= 0) {
                    clearInterval(timer);   //定时器清除；
                    history.back(-1);
                }
            }, 1000);

        }
$(function () {
    timer(intDiff);
});