原生JS实现DateTime格式化

利用正则Replace方法来简易实现：

<script>
    function date_format(format, time) {
        var t = typeof time !== 'undefined' ? new Date(time) : new Date();
        return format.replace(/Y|m|d|H|i|s/g, function (match) {
            switch (match) {
                case 'Y':
                    return filter(t.getFullYear());
                case 'm':
                    return filter(t.getMonth() + 1);
                case 'd':
                    return filter(t.getDate());
                case 'H':
                    return filter(t.getHours());
                case 'i':
                    return filter(t.getMinutes());
                case 's':
                    return filter(t.getSeconds());
            }
        });

        function filter(i) {
            return (i < 10 ? '0' : '') + i
        }
    }
</script>