JS ：Date日期格式化

Date.prototype.format = function (formatStr) {
    var date = this;
    /*  
    函数：填充0字符  
    参数：value-需要填充的字符串, length-总长度  
    返回：填充后的字符串  
    */
    var zeroize = function (value, length) {
        if (!length) {
            length = 2;
        }
        value = new String(value);
        for (var i = 0, zeros = ''; i < (length - value.length); i++) {
            zeros += '0';
        }
        return zeros + value;
    };
    return formatStr.replace(/"[^"]*"|'[^']*'|\b(?:d{1,4}|M{1,4}|yy(?:yy)?|([hHmstT])\1?|[lLZ])\b/g, function ($0) {
        switch ($0) {
            case 'd': return date.getDate();
            case 'dd': return zeroize(date.getDate());
            case 'ddd': return ['Sun', 'Mon', 'Tue', 'Wed', 'Thr', 'Fri', 'Sat'][date.getDay()];
            case 'dddd': return ['Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'][date.getDay()];
            case 'M': return date.getMonth() + 1;
            case 'MM': return zeroize(date.getMonth() + 1);
            case 'MMM': return ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec'][date.getMonth()];
            case 'MMMM': return ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December'][date.getMonth()];
            case 'yy': return new String(date.getFullYear()).substr(2);
            case 'yyyy': return date.getFullYear();
            case 'h': return date.getHours() % 12 || 12;
            case 'hh': return zeroize(date.getHours() % 12 || 12);
            case 'H': return date.getHours();
            case 'HH': return zeroize(date.getHours());
            case 'm': return date.getMinutes();
            case 'mm': return zeroize(date.getMinutes());
            case 's': return date.getSeconds();
            case 'ss': return zeroize(date.getSeconds());
            case 'l': return date.getMilliseconds();
            case 'll': return zeroize(date.getMilliseconds());
            case 'tt': return date.getHours() < 12 ? 'am' : 'pm';
            case 'TT': return date.getHours() < 12 ? 'AM' : 'PM';
        }
    });
}

   //增加天数
        function addDays(fDate, days) {
            var result;
            var time = new Date(fDate).getTime();
            var oneDayLong = 24 * 60 * 60 * 1000;
            result = time + days * oneDayLong;
            result = new Date(result).format("yyyy-MM-dd");
            return result;
        }