显示当前时间距离某一日期的时间倒计时

由于需求需要做中秋节抽奖 所以有一个倒计时，顺手记录下来了

可以把时间date对象转化成时间戳 根据时间戳来得出时间差

function countdown() {
            let nowDate = new Date();
            let nowDateChuo = Date.parse(nowDate); //转化成时间戳
            let midAutumn = new Date('2019-9-13 12:00:00');
            let midAutumneChuo = Date.parse(midAutumn);
            let date3 = midAutumneChuo - nowDateChuo;

            var days = Math.floor(date3 / (24 * 3600 * 1000));
            var leave1 = date3 % (24 * 3600 * 1000);
            var hours = Math.floor(leave1 / (3600 * 1000));
            var leave2 = leave1 % (3600 * 1000);
            var minutes = Math.floor(leave2 / (60 * 1000));
            var leave3 = leave2 % (60 * 1000);
            var seconds = Math.round(leave3 / 1000);
            if (hours < 10) hours = '0' + hours;
            if (minutes < 10) minutes = '0' + minutes;
            if (seconds < 10) seconds = '0' + seconds;
            $('.day').text(days);
            $('.hour').text(hours);
            $('.minutes').text(minutes);
            $('.second').text(seconds);
        }
        setInterval(countdown, 1000);

还有一种是根据年月日来计算 我这里没写

顺带记一下判断某个日期星期几 date提供了getDay()

        var date = "08/28/2019"; //此处也可以写成 17/07/2014 一样识别    也可以写成 07-17-2014  但需要正则转换   
        var day = new Date(Date.parse(date)); //需要正则转换的则 此处为 ： var day = new Date(Date.parse(date.replace(/-/g, '/')));  
        var today = new Array('星期日', '星期一', '星期二', '星期三', '星期四', '星期五', '星期六');//新建一个对应的中文星期数组
        var week = today[day.getDay()];
        //最终结果为：  
        console.log(week);

参考自https://www.cnblogs.com/haonanZhang/p/6855767.html