setInterval【计时器】

    ~function(){
        const nextPushTime = $('#nextPushTime_promotion_push');
        const prevTime = new Date('2017-11-12 16:53:00').getTime() + 2*24*60*60*1000;
        const nowTime = new Date().getTime();
        let seconds = prevTime - nowTime; //倒计时的秒数     
        let timer = setInterval(function (){
            num = seconds/1000;
            let text = '距离下次推送时间为：' + 
                        (Math.floor(num/86400) < 10 ? '0' + Math.floor(num/86400) :Math.floor(num/86400)) + 
                        '天' + 
                        (Math.floor(num%86400/3600) < 10 ? '0' + Math.floor(num%86400/3600):Math.floor(num%86400/3600)) +
                        '小时' + 
                        (Math.floor(num%3600/60) < 10 ? '0' + Math.floor(num%3600/60):Math.floor(num%3600/60))+ 
                        '分' + 
                        ((num%60).toFixed(0) < 10 ? '0' + (num%60).toFixed(0): (num%60).toFixed(0))
                        + '秒';
            if(num < 1000) {
                text = '您现在可发送促销推送';
                clearInterval(timer);
            }
            nextPushTime.text(text); 
            seconds = seconds -1000;
        }, 1000)
    }();