js 实现倒计时功能，兼容ios，类似京东

<div class="weui-cell count_down">
   <div class="weui-cell__bd">
        <p>秒杀中，抢到就是赚到</p>
    </div>
    <div class="weui-cell__ft">距结束 
        <span class="num">00</span>:
        <span class="num">00</span>:
        <span class="num">00</span>
    </div>
</div>

function antitime() {
        var time="2018-09-04 21:08:49";
        var to = new Date(time.replace(/-/g, "/"));
        var now = new Date();
        var deltaTime = to.getTime() - now.getTime();
        //超时就停止倒计时
        if (deltaTime <= 0) {
            window.clearInterval(timer);
            return;
        }
        var d= deltaTime / (1000 * 60 * 60 * 24);
        var h = Math.floor(deltaTime / 1000 / 60 / 60 % 24); 
        var m = Math.floor(deltaTime / 1000 / 60 % 60);
        var s = Math.floor(deltaTime / 1000 % 60);
        //把时间的数字转成字符串， 如果时分秒不足10， 则前面补0
        var timeStr = ""+ (h/10>=1?h=h:h="0"+h) + (m/10>=1?m=m:m="0"+m) + (s/10>=1?s=s:s="0"+s);
        //console.log(timeStr);
        //each循环遍历.num元素
        $(".weui-cell__ft .num").each(function(index, span) {
            $(span).html(timeStr.substring(index, index+2));
            if(index==1) $(span).html(timeStr.substring(2, 4));
            if(index==2) $(span).html(timeStr.substring(4, 6));
            //$(span).html();这个方法是用来设置span里面的值的
        });
    }
    //每秒执行一次
    var timer = setInterval(antitime, 1000);