JS如何将CST格式的日期转换为制定格式String

<html>
<body>

<script type="text/javascript">

var d = new Date()
　　dateFormat = function (date, format) {
            date = new Date(date);

            var o = {
                'M+' : date.getMonth() + 1, //month
                'd+' : date.getDate(), //day
                'H+' : date.getHours(), //hour
                'm+' : date.getMinutes(), //minute
                's+' : date.getSeconds(), //second
                'S' : date.getMilliseconds() //millisecond
            };

            if (/(y+)/.test(format))
                format = format.replace(RegExp.$1, (date.getFullYear() + '').substr(4 - RegExp.$1.length));

            for (var k in o)
                if (new RegExp('(' + k + ')').test(format))
                    format = format.replace(RegExp.$1, RegExp.$1.length == 1 ? o[k] : ('00' + o[k]).substr(('' + o[k]).length));

            return format;
        }

　　document.write (dateFormat('Mon Apr 27 09:08:20 CST 2015','yyyy-MM-dd HH:mm:ss'));

</script>

</body>
</html>