time.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>123</title>
    <script>
       
        function nowtt() {
            var time = new Date();
            var year = time.getFullYear();
            var month = time.getMonth() + 1;
            var day = time.getDate();
            var hour = time.getHours();
            var minute = time.getMinutes();
            var second = time.getSeconds();

            if (minute < 10) minute = '0' + minute;
            if (second < 10) second = '0' + second;

            var temp = year + "/" + month + "/" + day + " " + hour + ": " + minute + ":" + second;
            document.getElementById('time').innerHTML = temp;            
            setTimeout('nowtt()', 1000);
            
            return temp;
        }     
    </script>
</head>
<body onload="nowtt()">
    <span id="time"></span>    
</body>
</html>