用js写倒计时``````

<body>
    <div>
        <!-- 页面的块 -->
        <span id="days"></span>
        <span id="hour"></span>
        <span id="minute"></span>
        <span id="second"></span>
    </div>
    <script>
        // 调用函数
        countdown();
        //封装函数
        function countdown() {
            var date = new Date();
            // 将来要到的那个时间
            var jTime = +new Date('2020/11/11 12:00:00');
            // 获取到元素
            var days = document.getElementById("days");
            var hour = document.getElementById("hour");
            var minute = document.getElementById("minute");
            var second = document.getElementById("second");
            var newTime = +new Date();
            var allSecond = (jTime - newTime) / 1000;//转换秒数
            var d = parseInt(allSecond % 60);//秒数   
            d = d < 10 ? '0' + d : d;// 一位数的时候个位前+0   两位数输出原数
            var e = parseInt(allSecond / 60 % 60);//分钟
            e = e < 10 ? '0' + e : e;
            var f = parseInt(allSecond / 60 / 60 % 24);//小时
            f = f < 10 ? '0' + f : f;
            var g = parseInt(allSecond / 60 / 60 / 24);//天
            g = g < 10 ? '0' + g : g;
            // 在页面元素出现
            days.innerText = g + '天';
            hour.innerText = f + '时';
            minute.innerText = e + '分';
            second.innerText = d + '秒';
        }
        setInterval(countdown, 1000);


    </script>
</body>