倒计时！ - 掘金

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<html lang="en">

<head>
    <meta charset="UTF-8">
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    <title>Document</title>
</head>

<body>
    <h1 id="countdown"></h1>
    <script>
        function countdown() {
            //计算距离2020-02-14 17:30:00 有多少天，多少小时，多少分钟，多少秒？
            var start = new Date()
            var end = new Date("2020-02-14 17:30:00")

            //将一个日期对象向数字进行转换，会得到日期对象的时间戳
            var offset = end - start;

            //

            var days = Math.floor(offset / (1000 * 60 * 60 * 24))
            days = days < 10 ? "0" + days : days;
            var days_change = offset % (1000 * 60 * 60 * 24)

            var hours = Math.floor(days_change / (60 * 60 * 1000))
            hours = hours <10 ? "0" + hours :hours
            var hours_change = days_change % (60 * 60 * 1000)

            var minutes = Math.floor(hours_change / (60 * 1000))
            minutes = minutes < 10 ? "0" + minutes : minutes
            var minutes_change = Math.floor(hours_change % (60 * 1000))

            var seconds = Math.floor(minutes_change / (1000))
            seconds = seconds < 10 ? "0" + seconds :seconds

            var str = days + ":" + hours + ":" + minutes + ":" + seconds

            var countdown_1 = document.getElementById("countdown");
            // countdown_1.innerHTML = days + ":" + hours + ":" + minutes + ":" + seconds
            countdown_1.innerHTML = str
        }

        countdown();

        setInterval(function () {//每一秒调用一次
            countdown()
        }, 1000);
    </script>
</body>

</html>