CountNumber.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>CountNumber</title>
    <link href="https://fonts.googleapis.com/css?family=Varela+Round" rel="stylesheet">
    <style>
        h1 {
            font-family: 'Varela Round', sans-serif;
            font-size: 15em;
            text-align: center;
            color: orangered;
        }
        body {
            background-color: orange;
        }
    </style>
</head>
<body>
    <h1 id="count"></h1>
    <script>
        var number = 30;
        var countDown = setInterval(function () {
            document.getElementById('count').innerHTML = number;
            if (number > 0) {
                --number; // Decrease one Second Every 1000 Millisecond  
            } else {
                clearInterval(countDown); // Stop CountDown Timer
                document.getElementById('count').innerHTML = "หยุด";
            }
        }, 1000);
        //read more: https://github.com/kkenth007/Data-structure-PDF/blob/master/CountNumber.pdf
    </script>
</body>
</html>