毫秒级倒计时

function countTime() {
        let endDateDefault = '2021-04-17 10:59:59';
        const date = new Date();
        const now = date.getTime();
        const endDate = new Date(endDateDefault);//设置截止时间
        const end = endDate.getTime();
        const leftTime = end - now; //时间差
        let d, h, m, s, ms;
        if (leftTime >= 0) {
            // 天
            d = Math.floor(leftTime / 1000 / 60 / 60 / 24);
            // 小时
            h = Math.floor(leftTime / 1000 / 60 / 60 % 24);
            // 分钟
            m = Math.floor(leftTime / 1000 / 60 % 60);
            // 秒
            s = Math.floor(leftTime / 1000 % 60);
            // 毫秒
            ms = Math.floor(leftTime % 1000);
            ms = ms < 100 ? "0" + ms : ms;
            s = s < 10 ? "0" + s : s;
            m = m < 10 ? "0" + m : m;
            h = h < 10 ? "0" + h : h;
            console.log('倒计时:'+d+' '+h+':'+m+":"+s+":"+ms);
        } else {
            console.log('已截止');
            clearInterval(clearTime);
        }
    }
    //递归每秒调用countTime方法，显示动态时间效果
    const clearTime = setInterval(countTime, 50);