js实现倒计时

    //倒计时8分钟
    var getTime=sessionStorage.getItem("zicetime");
    var intDiff = parseInt(getTime * 60);//倒计时总秒数量
    function timer(intDiff){
        window.setInterval(function(){
        var day=0,
            hour=0,
            minute=0,
            second=0;//时间默认值        
        if(intDiff > 0){
            day = Math.floor(intDiff / (60 * 60 * 24));
            hour = Math.floor(intDiff / (60 * 60)) - (day * 24);
            minute = Math.floor(intDiff / 60) - (day * 24 * 60) - (hour * 60);
            second = Math.floor(intDiff) - (day * 24 * 60 * 60) - (hour * 60 * 60) - (minute * 60);
        }
        if (minute <= 9) minute = ‘0‘ + minute;
        if (second <= 9) second = ‘0‘ + second;
       // $(‘#day_show‘).html(day+"天");
        $(‘#hour_show‘).html(‘<s id="h"></s>‘+hour+‘时‘);
        $(‘#minute_show‘).html(‘<s></s>‘+minute+‘分‘);
        $(‘#second_show‘).html(‘<s></s>‘+second+‘秒‘);
        intDiff--;

        // if(intDiff==50){
        //   alert(123)
        // }
        }, 1000);
    } 
    $(function(){
        timer(intDiff);
    });