index.js

var dateFormat = function () {
	var	token = /d{1,4}|m{1,4}|yy(?:yy)?|([HhMsTt])\1?|[LloSZ]|"[^"]*"|'[^']*'/g,
		timezone = /\b(?:[PMCEA][SDP]T|(?:Pacific|Mountain|Central|Eastern|Atlantic) (?:Standard|Daylight|Prevailing) Time|(?:GMT|UTC)(?:[-+]\d{4})?)\b/g,
		timezoneClip = /[^-+\dA-Z]/g,
		pad = function (val, len) {
			val = String(val);
			len = len || 2;
			while (val.length < len) val = "0" + val;
			return val;
		};

	return function (date, mask, utc) {
		var dF = dateFormat;

		if (arguments.length == 1 && Object.prototype.toString.call(date) == "[object String]" && !/\d/.test(date)) {
			mask = date;
			date = undefined;
		}
		date = date ? new Date(date) : new Date;
		if (isNaN(date)) throw SyntaxError("invalid date");

		mask = String(dF.masks[mask] || mask || dF.masks["default"]);

		if (mask.slice(0, 4) == "UTC:") {
			mask = mask.slice(4);
			utc = true;
		}

		var	_ = utc ? "getUTC" : "get",
			d = date[_ + "Date"](),
			D = date[_ + "Day"](),
			m = date[_ + "Month"](),
			y = date[_ + "FullYear"](),
			H = date[_ + "Hours"](),
			M = date[_ + "Minutes"](),
			s = date[_ + "Seconds"](),
			L = date[_ + "Milliseconds"](),
			o = utc ? 0 : date.getTimezoneOffset(),
			flags = {
				d:    d,
				dd:   pad(d),
				ddd:  dF.i18n.dayNames[D],
				dddd: dF.i18n.dayNames[D + 7],
				m:    m + 1,
				mm:   pad(m + 1),
				mmm:  dF.i18n.monthNames[m],
				mmmm: dF.i18n.monthNames[m + 12],
				yy:   String(y).slice(2),
				yyyy: y,
				h:    H % 12 || 12,
				hh:   pad(H % 12 || 12),
				H:    H,
				HH:   pad(H),
				M:    M,
				MM:   pad(M),
				s:    s,
				ss:   pad(s),
				l:    pad(L, 3),
				L:    pad(L > 99 ? Math.round(L / 10) : L),
				t:    H < 12 ? "a"  : "p",
				tt:   H < 12 ? "am" : "pm",
				T:    H < 12 ? "A"  : "P",
				TT:   H < 12 ? "AM" : "PM",
				Z:    utc ? "UTC" : (String(date).match(timezone) || [""]).pop().replace(timezoneClip, ""),
				o:    (o > 0 ? "-" : "+") + pad(Math.floor(Math.abs(o) / 60) * 100 + Math.abs(o) % 60, 4),
				S:    ["th", "st", "nd", "rd"][d % 10 > 3 ? 0 : (d % 100 - d % 10 != 10) * d % 10]
			};

		return mask.replace(token, function ($0) {
			return $0 in flags ? flags[$0] : $0.slice(1, $0.length - 1);
		});
	};
}();

dateFormat.masks = {
	"default":      "ddd mmm dd yyyy HH:MM:ss",
	shortDate:      "m/d/yy",
	mediumDate:     "mmm d, yyyy",
	longDate:       "mmmm d, yyyy",
	fullDate:       "dddd, mmmm d, yyyy",
	shortTime:      "h:MM TT",
	mediumTime:     "h:MM:ss TT",
	longTime:       "h:MM:ss TT Z",
	isoDate:        "yyyy-mm-dd",
	isoTime:        "HH:MM:ss",
	isoDateTime:    "yyyy-mm-dd'T'HH:MM:ss",
	isoUtcDateTime: "UTC:yyyy-mm-dd'T'HH:MM:ss'Z'"
};

dateFormat.i18n = {
	dayNames: [
		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
		"Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"
	],
	monthNames: [
		"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec",
		"January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"
	]
};

var strtotime = function (text, now) {
    var parsed, match, year, date, days, ranges, len, times, regex, i;

    if (!text) {
        return null;
    }
    // Unecessary spaces
    text = text.trim()
        .replace(/\s{2,}/g, ' ')
        .replace(/[\t\r\n]/g, '')
        .toLowerCase();

    if (text === 'now') {
        return now === null || isNaN(now) ? new Date().getTime() / 1000 | 0 : now | 0;
    }
    if (!isNaN(parsed = Date.parse(text))) {
        return parsed / 1000 | 0;
    }
    if (text === 'now') {
        return new Date().getTime() / 1000; // Return seconds, not milli-seconds
    }
    if (!isNaN(parsed = Date.parse(text))) {
        return parsed / 1000;
    }

    match = text.match(/^(\d{2,4})-(\d{2})-(\d{2})(?:\s(\d{1,2}):(\d{2})(?::\d{2})?)?(?:\.(\d+)?)?$/);
    if (match) {
        year = match[1] >= 0 && match[1] <= 69 ? +match[1] + 2000 : match[1];
        return new Date(year, parseInt(match[2], 10) - 1, match[3],
            match[4] || 0, match[5] || 0, match[6] || 0, match[7] || 0) / 1000;
    }

    date = now ? new Date(now * 1000) : new Date();
    days = {
        'sun': 0,
        'mon': 1,
        'tue': 2,
        'wed': 3,
        'thu': 4,
        'fri': 5,
        'sat': 6
    };
    ranges = {
        'yea': 'FullYear',
        'mon': 'Month',
        'day': 'Date',
        'hou': 'Hours',
        'min': 'Minutes',
        'sec': 'Seconds'
    };

    function lastNext(type, range, modifier) {
        var diff, day = days[range];

        if (typeof day !== 'undefined') {
            diff = day - date.getDay();

            if (diff === 0) {
                diff = 7 * modifier;
            }
            else if (diff > 0 && type === 'last') {
                diff -= 7;
            }
            else if (diff < 0 && type === 'next') {
                diff += 7;
            }

            date.setDate(date.getDate() + diff);
        }
    }
    function process(val) {
        var splt = val.split(' '),
            type = splt[0],
            range = splt[1].substring(0, 3),
            typeIsNumber = /\d+/.test(type),
            ago = splt[2] === 'ago',
            num = (type === 'last' ? -1 : 1) * (ago ? -1 : 1);

        if (typeIsNumber) {
            num *= parseInt(type, 10);
        }

        if (ranges.hasOwnProperty(range) && !splt[1].match(/^mon(day|\.)?$/i)) {
            return date['set' + ranges[range]](date['get' + ranges[range]]() + num);
        }
        if (range === 'wee') {
            return date.setDate(date.getDate() + (num * 7));
        }

        if (type === 'next' || type === 'last') {
            lastNext(type, range, num);
        }
        else if (!typeIsNumber) {
            return false;
        }
        return true;
    }

    times = '(years?|months?|weeks?|days?|hours?|minutes?|min|seconds?|sec' +
        '|sunday|sun\\.?|monday|mon\\.?|tuesday|tue\\.?|wednesday|wed\\.?' +
        '|thursday|thu\\.?|friday|fri\\.?|saturday|sat\\.?)';
    regex = '([+-]?\\d+\\s' + times + '|' + '(last|next)\\s' + times + ')(\\sago)?';

    match = text.match(new RegExp(regex, 'gi'));
    if (!match) {
        return false;
    }

    for (i = 0, len = match.length; i < len; i++) {
        if (!process(match[i])) {
            return false;
        }
    }
	
    return date;
}

Date.prototype.format = function (mask, utc) {
	return dateFormat(this, mask, utc);
};

Date.prototype.strtotime = function (string) {
	return strtotime(string, this.getTime()/1000);
};