SOURCE

/**
 * 操作页面 倒计时模块的 时间节点
 * @param {Object} minute 分
 * @param {Object} second 秒
 * @param {Object} millisecond 毫秒
 */
function timingInterVal(minute, second, millisecond) {
    var timing = setInterval(function () {
        //设置毫秒数
        if ((Number(millisecond.innerHTML)) <= 0) {
            //设置秒数
            if ((Number(second.innerHTML)) <= 0) {
                //设置分数
                if ((Number(minute.innerHTML)) <= 0) {
                    //分钟倒计时结束
                    clearInterval(timing);
                    //结束 具体操作
                    return false;
                } else {
                    (Number(minute.innerHTML)) <= 10 ? minute.innerHTML = ('0' + ((Number(minute.innerHTML)) - 1)) : minute.innerHTML = ((Number(minute.innerHTML)) - 1);
                }
                second.innerHTML = '60';
            } else {
                (Number(second.innerHTML)) <= 10 ? second.innerHTML = ('0' + ((Number(second.innerHTML)) - 1)) : second.innerHTML = ((Number(second.innerHTML)) - 1);
            }
            millisecond.innerHTML = '99';
        } else {
            (Number(millisecond.innerHTML)) <= 10 ? millisecond.innerHTML = ('0' + (Number(millisecond.innerHTML) - 1)) : millisecond.innerHTML = (Number(millisecond.innerHTML) - 1);
        }
    }, 16);
}
const btn = document.getElementById('btn')
console.log(btn)
btn.onclick = function () {
    //遍历页面中定义的 存在的倒计时 HTML 模块。
    var timing = document.getElementsByClassName('timing');
    for (var i = 0; i < timing.length; i++) {
        //分
        var minute = timing[i].querySelector('.minute');
        //秒
        var second = timing[i].querySelector('.second');
        //毫秒
        var millisecond = timing[i].querySelector('.millisecond');

        timingInterVal(minute, second, millisecond);
    }
}

<!-- 构建 HTML -->
<div class="timing">
	<span class="minute date">00</span>
	<span class="colon">:</span>
	<span class="second date">15</span>
	<span class="colon">:</span>
	<span class="millisecond date">00</span>
</div>
<button id="btn">开始</button>

.timing {
    color: #ed4123;
    font-size: 20px;
    font-weight: 600;
    font-family: sans-serif;
    display: flex;
}

.timing > span {
    display: block;
    float: left;
}

.date {
    width: 35px;
    text-align: center;
}