A JavaScript date format inspired by the .NET framework

format-date.js

// Date Format function
// 
// Format options inspired by the .NET framework's format.
// http://msdn.microsoft.com/en-us/library/8kb3ddd4.aspx
//
// Non-formatting characters within the format string must be 
// quoted (single (') or double (") quotes)! The same is true 
// for two format specifiers that should apear together. Eg. 
// if you want the date to be output with the date ordinal 
// (9th), the format string must be "d''x" (or 'd""x'). 
//
// Copyright (c) Martin Lundgren, 2011
//
// Arguments: 
//     format   {String} The format pattern to display the date in. See Format Patterns section below for options.
//     settings {Object} Formatting settings. 
//
// Settings:
//     asUtc      {Boolean} If the formatted date is to be returned as a UTC date. 
//     days       {Array}   The days of the week. Starting with Sunday.
//     daysAbbr   {Array}   The days of the week, abbreviated. Starting with Sunday.
//     designator {Array}   Time designator. Starting with AM. 
//     format     {String}  The format pattern to format the date in.
//     months     {Array}   The name of the months. Starting with January.
//     monthsAbbr {Array}   The name of the months, abbreviated. Starting with January.
// 
// Format Patterns:
//      d       1-31                The day of the month
//      dd      01-31               The day of the month
//      ddd     Mon-Sun             The abbreviated name of the day of the week
//      dddd    Monday-Sunday       The full name of the day of the week
//      f       6                   The tenths of a second in a date and time value. The remaining digits are truncated. 
//      ff      61                  The hundredths of a second in a date and time value. The remaining digits are truncated. 
//      fff     617                 The milliseconds in a date and time value. The remaining digits are truncated. 
//      ffff    6170                The milliseconds in a date and time value, with a trailing zero. The remaining digits are truncated. 
//      fffff   61700               The milliseconds in a date and time value, with two trailing zeros. The remaining digits are truncated. 
//      ffffff  617000              The milliseconds in a date and time value, with three trailing zeros. The remaining digits are truncated.
//      F       6                   The tenths of a second in a date and time value. Trailing zeros or zero values are not displayed. 
//      FF      61                  The hundredths of a second in a date and time value. Trailing zeros or zero values are not displayed. 
//      FFF     617                 The milliseconds in a date and time value. Trailing zeros or zero values are not displayed. 
//      FFFF    617                 The milliseconds in a date and time value. Trailing zeros or zero values are not displayed. 
//      FFFFF   617                 The milliseconds in a date and time value. Trailing zeros or zero values are not displayed. 
//      FFFFFF  617                 The milliseconds in a date and time value. Trailing zeros or zero values are not displayed. 
//      h       1-12                The hour, using a 12-hour clock
//      hh      01-12               The hour, using a 12-hour clock
//      H       0-23                The hour, using a 24-hour clock
//      HH      00-23               The hour, using a 24-hour clock
//      m       0-59                The minute
//      mm      00-59               The minute
//      M       1-12                The month
//      MM      01-12               The month
//      MMM     Jan-Dec             The abbreviated name of the month
//      MMMM    January-December    The full name of the month
//      s       0-59                The second
//      ss      00-59               The second
//      tt      AM/PM               The AM/PM designator
//      x       st, nd, rd, th      The ordinal suffix of a number (NOTE! This does not exist in .NET!) 
//      y       0-99                The year
//      yy      00-99               The year
//      yyy     001-9999            The year, with a minimum of three digits
//      yyyy    0001-9999           The year as a four-digit number
//      z       +1                  Hours offset from UTC, with no leading zeros.
//      zz      +01                 Hours offset from UTC, with a leading zero for a single-digit value.
//      zzz     +01:00              Hours and minutes offset from UTC.
//
// Example:
//     The formatting method can be called in the following three ways: 
//     fn(format, settings) {String} The format string passed is used, any settings are stored. 
//                                   If the settings object contain a format property, it will override the format string. 
//     fn(settings)         {String} Settings are stored and the stored format is used. 
//     fn()                 {String} Default settings are used. 
//
(function () {

    'use strict';

    var _asUtc = false,
        _days = 'Sunday Monday Tuesday Wednesday Thursday Friday Saturday'.split(' '),
        _daysAbbr = 'Sun Mon Tue Wed Thu Fri Sat'.split(' '),
        _designator = 'AM PM'.split(' '),
        _format = 'MMMM d""x "at" h:mm tt',
        _months = 'January February March April May June July August September October November December'.split(' '),
        _monthsAbbr = 'Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec'.split(' '),

        // The formatting function 
        _toFormat = function () {
            var _this = this, dateMethod, find, format, methods, settings, str;
            // Evaluate arguments
            if (typeof arguments[0] === 'string') {
                format = arguments[0];
                settings = arguments[1];
            }
            else {
                format = null;
                settings = arguments[0];
            }
            // Store any passed settings
            if (settings) {
                if (typeof settings.asUtc !== 'undefined') _asUtc = settings.asUtc;
                if (settings.days) _days = settings.days;
                if (settings.daysAbbr) _daysAbbr = settings.daysAbbr;
                if (settings.designator) _designator = settings.designator;
                if (settings.format) _format = settings.format;
                if (settings.getDateOrdinal) _getDateOrdinal = settings.getDateOrdinal;
                if (settings.months) _months = settings.months;
                if (settings.monthsAbbr) _monthsAbbr = settings.monthsAbbr;
            }
            if (!format) {
                format = _format;
            }
            dateMethod = function (method) {
                return 'get' + (_asUtc ? 'UTC' : '') + method;
            };
            methods = {
                     d: function () { return this[dateMethod('Date')](); },
                    dd: function () { return _pad(this[dateMethod('Date')]()); },
                   ddd: function () { return _getDayName.call(this, true); },
                  dddd: function () { return _getDayName.call(this); },
                     f: function () { return _pad(_pad(this[dateMethod('Milliseconds')](), 3), 6, true).substr(0, 1); },
                    ff: function () { return _pad(_pad(this[dateMethod('Milliseconds')](), 3), 6, true).substr(0, 2); },
                   fff: function () { return _pad(_pad(this[dateMethod('Milliseconds')](), 3), 6, true).substr(0, 3); },
                  ffff: function () { return _pad(_pad(this[dateMethod('Milliseconds')](), 3), 6, true).substr(0, 4); },
                 fffff: function () { return _pad(_pad(this[dateMethod('Milliseconds')](), 3), 6, true).substr(0, 5); },
                ffffff: function () { return _pad(_pad(this[dateMethod('Milliseconds')](), 3), 6, true).substr(0, 6); },
                     F: function () { var r = _pad(this[dateMethod('Milliseconds')](), 3).substr(0, 1); return r === '0' ? '' : r; },
                    FF: function () { var r = _pad(this[dateMethod('Milliseconds')](), 3).substr(0, 2); return r === '00' ? '' : r; },
                   FFF: function () { return _pad(this[dateMethod('Milliseconds')](), 3).substr(0, 3); },
                  FFFF: function () { return methods.FFF.call(this); },
                 FFFFF: function () { return methods.FFF.call(this); },
                FFFFFF: function () { return methods.FFF.call(this); },
                     h: function () { var h = this[dateMethod('Hours')](); return h > 12 ? h - 12 : h; },
                    hh: function () { var h = this[dateMethod('Hours')](); return _pad(h > 12 ? h - 12 : h); },
                     m: function () { return this[dateMethod('Minutes')](); },
                    mm: function () { return _pad(this[dateMethod('Minutes')]()); },
                     H: function () { return this[dateMethod('Hours')](); },
                    HH: function () { return _pad(this[dateMethod('Hours')]()); },
                     M: function () { return this[dateMethod('Month')]() + 1; },
                    MM: function () { return _pad(this[dateMethod('Month')]() + 1); },
                   MMM: function () { return _getMonthName.call(this, true); },
                  MMMM: function () { return _getMonthName.call(this); },
                     s: function () { return this[dateMethod('Seconds')](); },
                    ss: function () { return _pad(this[dateMethod('Seconds')]()); },
                    tt: function () { return _getTimeDesignator.call(this); },
                     x: function () { return _getDateOrdinal.call(this); },
                     y: function () { var y = this[dateMethod('FullYear')](), s = y.toString(); return y < 10 ? y : s.substr(s.length - 2); },
                    yy: function () { return _pad(this[dateMethod('FullYear')](), 2); },
                   yyy: function () { var y = this[dateMethod('FullYear')](), s = y.toString(); return y < 1000 ? _pad(y, 3) : s.substr(s.length - 4); },
                  yyyy: function () { return _pad(this[dateMethod('FullYear')](), 4); },
                 yyyyy: function () { return _pad(this[dateMethod('FullYear')](), 5); },
                yyyyyy: function () { return _pad(this[dateMethod('FullYear')](), 6); },
                     z: function () { var t = this.getTimezoneOffset(); return (t > 0 ? '-' : '+') + Math.abs(t / 60); },
                    zz: function () { var t = this.getTimezoneOffset(); return (t > 0 ? '-' : '+') + _pad(Math.abs(t / 60)); },
                   zzz: function () { var t = this.getTimezoneOffset(); return (t > 0 ? '-' : '+') + _pad(Math.abs(t / 60)) + ':' + _pad((Math.abs(t / 60) % 1) * 60); }
            };
            find = /([dfFhmHMstxyz]+)(?=([^"']*["'][^"']*["'])*[^"']*$)/g;
            str = format.replace(find, function (match, group1) {
                var fn = methods[group1];
                return typeof fn === 'function' ? fn.call(_this) : match;
            });
            return str.replace(/["']/g, '');
        },

        _getDayName = function (asAbbr) {
            var n = this.getDay();
            return asAbbr ? _daysAbbr[n] : _days[n];
        },

        _getDateOrdinal = (function () {
            var sf = ['th', 'st', 'nd', 'rd', 'th'];
            return function () {
                var d = this.getDate();
                return (d > 3 && d < 21) ? 'th' : sf[Math.min(d % 10, 4)];
            };
        } ()),

        _getMonthName = function (asAbbr) {
            var n = this.getMonth();
            return asAbbr ? _monthsAbbr[n] : _months[n];
        },

        _getTimeDesignator = function () {
            return this.getHours() >= 12 ? _designator[1] : _designator[0];
        },

        _pad = function (o, l, r) {
            if (r) {
                return (o + '000000').slice(0, l ? Math.min(l, 6) : 2);
            }
            else {
                return ('000000' + o).slice(-(l ? Math.min(l, 6) : 2));
            }
        };

    // Expose the formatting method
    // As a global function
    //window.formatDate = function (date, format, options) {
    //    if(isNaN(+date) || !date.getDate) throw new Error('Not a valid date');
    //    return _toFormat.call(date, format, options);
    //};
    // Or as a method on the Date object
    Date.prototype.format = function (format, options) {
        return _toFormat.call(this, format, options);
    };

} ());

Nice work.