js正则表达式匹配一个时间格式的字符串-长跑茗

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <script src="https://asset.cpming.top/js-myutils/jquery-1.12.3.min.js"></script>
    <title>验证时间</title>
    <script type="text/javascript">
        function validateDateTime(testdate) {
            var date_regex = /((19|20)[0-9]{2})-(0?[1-9]|1[012])-(0?[1-9]|[12][0-9]|3[01]) ([01]?[0-9]|2[0-3]):[0-5]?[0-9]:[0-5]?[0-9]/;
            var res = date_regex.test(testdate);
            if(res) {
                var ymd = testdate.match(/(\d{4})-(\d+)-(\d+).*/);
                var year = parseInt(ymd[1]);
                var month = parseInt(ymd[2]);
                var day = parseInt(ymd[3]);
                if(day > 28) {
                    //获取当月的最后一天
                    var lastDay = new Date(year, month, 0).getDate();
                    return (lastDay >= day);
                }
                return true;
            }
            return false;
        }
        $(function (){
            $("#validate-btn").click(function (){
                var format = $("#time").val();
                var result = validateDateTime(format);
                $("#result").html("结果：" + result);
            });
        });
    </script>
    <style type="text/css">
        div {margin: 10px;}
        input {width: 250px; height: 30px; font-size: 14px; margin: 0px; padding: 0px;}
        button {width: 100px; height: 30px; margin: 0px; padding: 0px; font-size: 14px;}
    </style>
</head>
<body>
    <div>
        <p>此示例仅验证类似 2018-02-28 12:00:22 的时间格式</p>
        <p>请输入时间，如 2018-02-28 12:00:22</p>
        <input id="time" placeholder="请输入时间" />
        <button id="validate-btn">验证</button>
    </div>
    <div id="result"></div>
</body>
</html>