ios系统屏幕休眠或后台运行倒计时暂停问题

　   function Time_a() {
                var time = 10;
                $(".time").text(time);
                var t = setInterval(function() {
                    if(time == 0) {
                        clearTimeout(t);
                    } else {
                        time--；
                        $(".time").text(time)
                    }
                }, 1000)
         }

 function Time_b(){
                var time=10;
                var beginTime=new Date().getTime();
                $(".time-a").text(time);
                var t= setInterval(function(){
                    var newTime=new Date().getTime();
                    var dTime=(newTime-beginTime)/1000;
                    dTime=parseInt(dTime);
                    time = 10-dTime > 0 ? 10-dTime : 0;
                    $(".time-a").text(time);
                },1000)
            }