WordPress' date_i18n as javascript function (derived from phpjs date)

date_i18n.js

function date_i18n(format, timestamp) {
  // http://kevin.vanzonneveld.net
  // +   original by: Carlos R. L. Rodrigues (http://www.jsfromhell.com)
  // +      parts by: Peter-Paul Koch (http://www.quirksmode.org/js/beat.html)
  // +   improved by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +   improved by: MeEtc (http://yass.meetcweb.com)
  // +   improved by: Brad Touesnard
  // +   improved by: Tim Wiel
  // +   improved by: Bryan Elliott
  // +   improved by: David Randall
  // +      input by: Brett Zamir (http://brett-zamir.me)
  // +   bugfixed by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +   improved by: Theriault
  // +  derived from: gettimeofday
  // +      input by: majak
  // +   bugfixed by: majak
  // +   bugfixed by: Kevin van Zonneveld (http://kevin.vanzonneveld.net)
  // +      input by: Alex
  // +   bugfixed by: Brett Zamir (http://brett-zamir.me)
  // +   improved by: Theriault
  // +   improved by: Brett Zamir (http://brett-zamir.me)
  // +   improved by: Theriault
  // +   improved by: Thomas Beaucourt (http://www.webapp.fr)
  // +   improved by: JT
  // +   improved by: Theriault
  // +   improved by: Rafał Kukawski (http://blog.kukawski.pl)
  // +   bugfixed by: omid (http://phpjs.org/functions/380:380#comment_137122)
  // +      input by: Martin
  // +      input by: Alex Wilson
  // +      input by: Haravikk
  // +   improved by: Theriault
  // +   bugfixed by: Chris (http://www.devotis.nl/)
  // +   improved by: Jari Pennanen (https://github.com/ciantic/) - date_i18n from WordPress
  // %        note 1: Uses global: php_js to store the default timezone
  // %        note 2: Although the function potentially allows timezone info (see notes), it currently does not set
  // %        note 2: per a timezone specified by date_default_timezone_set(). Implementers might use
  // %        note 2: this.php_js.currentTimezoneOffset and this.php_js.currentTimezoneDST set by that function
  // %        note 2: in order to adjust the dates in this function (or our other date functions!) accordingly
  // *     example 1: date('H:m:s \\m \\i\\s \\m\\o\\n\\t\\h', 1062402400);
  // *     returns 1: '09:09:40 m is month'
  // *     example 2: date('F j, Y, g:i a', 1062462400);
  // *     returns 2: 'September 2, 2003, 2:26 am'
  // *     example 3: date('Y W o', 1062462400);
  // *     returns 3: '2003 36 2003'
  // *     example 4: x = date('Y m d', (new Date()).getTime()/1000);
  // *     example 4: (x+'').length == 10 // 2009 01 09
  // *     returns 4: true
  // *     example 5: date('W', 1104534000);
  // *     returns 5: '53'
  // *     example 6: date('B t', 1104534000);
  // *     returns 6: '999 31'
  // *     example 7: date('W U', 1293750000.82); // 2010-12-31
  // *     returns 7: '52 1293750000'
  // *     example 8: date('W', 1293836400); // 2011-01-01
  // *     returns 8: '52'
  // *     example 9: date('W Y-m-d', 1293974054); // 2011-01-02
  // *     returns 9: '52 2011-01-02'
    var that = this,
      jsdate,
      f,
      // Keep this here (works, but for code commented-out
      // below for file size reasons)
      //, tal= [],            
      // trailing backslash -> (dropped)
      // a backslash followed by any character (including backslash) -> the character
      // empty string -> empty string
      formatChr = /\\?(.?)/gi,
      formatChrCb = function (t, s) {
        return f[t] ? f[t]() : s;
      },
      _pad = function (n, c) {
        n = String(n);
        while (n.length < c) {
          n = '0' + n;
        }
        return n;
      };
  f = {
    // Day
    d: function () { // Day of month w/leading 0; 01..31
      return _pad(f.j(), 2);
    },
    D: function () { // Shorthand day name; Mon...Sun
      return DATE_I18N.day_names_short[f.w()];
    },
    j: function () { // Day of month; 1..31
      return jsdate.getDate();
    },
    l: function () { // Full day name; Monday...Sunday
      return DATE_I18N.day_names[f.w()];
    },
    N: function () { // ISO-8601 day of week; 1[Mon]..7[Sun]
      return f.w() || 7;
    },
    S: function(){ // Ordinal suffix for day of month; st, nd, rd, th
      var j = f.j(),
        i = j%10;
      if (i <= 3 && parseInt((j%100)/10, 10) == 1) {
        i = 0;
      }
      return ['st', 'nd', 'rd'][i - 1] || 'th';
    },
    w: function () { // Day of week; 0[Sun]..6[Sat]
      return jsdate.getDay();
    },
    z: function () { // Day of year; 0..365
      var a = new Date(f.Y(), f.n() - 1, f.j()),
        b = new Date(f.Y(), 0, 1);
      return Math.round((a - b) / 864e5);
    },

    // Week
    W: function () { // ISO-8601 week number
      var a = new Date(f.Y(), f.n() - 1, f.j() - f.N() + 3),
        b = new Date(a.getFullYear(), 0, 4);
      return _pad(1 + Math.round((a - b) / 864e5 / 7), 2);
    },

    // Month
    F: function () { // Full month name; January...December
      return DATE_I18N.month_names[f.n() - 1];
    },
    m: function () { // Month w/leading 0; 01...12
      return _pad(f.n(), 2);
    },
    M: function () { // Shorthand month name; Jan...Dec
      return DATE_I18N.month_names_short[f.n() - 1];
    },
    n: function () { // Month; 1...12
      return jsdate.getMonth() + 1;
    },
    t: function () { // Days in month; 28...31
      return (new Date(f.Y(), f.n(), 0)).getDate();
    },

    // Year
    L: function () { // Is leap year?; 0 or 1
      var j = f.Y();
      return j % 4 === 0 & j % 100 !== 0 | j % 400 === 0;
    },
    o: function () { // ISO-8601 year
      var n = f.n(),
        W = f.W(),
        Y = f.Y();
      return Y + (n === 12 && W < 9 ? 1 : n === 1 && W > 9 ? -1 : 0);
    },
    Y: function () { // Full year; e.g. 1980...2010
      return jsdate.getFullYear();
    },
    y: function () { // Last two digits of year; 00...99
      return f.Y().toString().slice(-2);
    },

    // Time
    a: function () { // am or pm
      return jsdate.getHours() > 11 ? "pm" : "am";
    },
    A: function () { // AM or PM
      return f.a().toUpperCase();
    },
    B: function () { // Swatch Internet time; 000..999
      var H = jsdate.getUTCHours() * 36e2,
        // Hours
        i = jsdate.getUTCMinutes() * 60,
        // Minutes
        s = jsdate.getUTCSeconds(); // Seconds
      return _pad(Math.floor((H + i + s + 36e2) / 86.4) % 1e3, 3);
    },
    g: function () { // 12-Hours; 1..12
      return f.G() % 12 || 12;
    },
    G: function () { // 24-Hours; 0..23
      return jsdate.getHours();
    },
    h: function () { // 12-Hours w/leading 0; 01..12
      return _pad(f.g(), 2);
    },
    H: function () { // 24-Hours w/leading 0; 00..23
      return _pad(f.G(), 2);
    },
    i: function () { // Minutes w/leading 0; 00..59
      return _pad(jsdate.getMinutes(), 2);
    },
    s: function () { // Seconds w/leading 0; 00..59
      return _pad(jsdate.getSeconds(), 2);
    },
    u: function () { // Microseconds; 000000-999000
      return _pad(jsdate.getMilliseconds() * 1000, 6);
    },

    // Timezone
    e: function () { // Timezone identifier; e.g. Atlantic/Azores, ...
      // The following works, but requires inclusion of the very large
      // timezone_abbreviations_list() function.
/*              return that.date_default_timezone_get();
*/
      throw 'Not supported (see source code of date() for timezone on how to add support)';
    },
    I: function () { // DST observed?; 0 or 1
      // Compares Jan 1 minus Jan 1 UTC to Jul 1 minus Jul 1 UTC.
      // If they are not equal, then DST is observed.
      var a = new Date(f.Y(), 0),
        // Jan 1
        c = Date.UTC(f.Y(), 0),
        // Jan 1 UTC
        b = new Date(f.Y(), 6),
        // Jul 1
        d = Date.UTC(f.Y(), 6); // Jul 1 UTC
      return ((a - c) !== (b - d)) ? 1 : 0;
    },
    O: function () { // Difference to GMT in hour format; e.g. +0200
      var tzo = jsdate.getTimezoneOffset(),
        a = Math.abs(tzo);
      return (tzo > 0 ? "-" : "+") + _pad(Math.floor(a / 60) * 100 + a % 60, 4);
    },
    P: function () { // Difference to GMT w/colon; e.g. +02:00
      var O = f.O();
      return (O.substr(0, 3) + ":" + O.substr(3, 2));
    },
    T: function () { // Timezone abbreviation; e.g. EST, MDT, ...
      // The following works, but requires inclusion of the very
      // large timezone_abbreviations_list() function.
/*              var abbr = '', i = 0, os = 0, default = 0;
      if (!tal.length) {
        tal = that.timezone_abbreviations_list();
      }
      if (that.php_js && that.php_js.default_timezone) {
        default = that.php_js.default_timezone;
        for (abbr in tal) {
          for (i=0; i < tal[abbr].length; i++) {
            if (tal[abbr][i].timezone_id === default) {
              return abbr.toUpperCase();
            }
          }
        }
      }
      for (abbr in tal) {
        for (i = 0; i < tal[abbr].length; i++) {
          os = -jsdate.getTimezoneOffset() * 60;
          if (tal[abbr][i].offset === os) {
            return abbr.toUpperCase();
          }
        }
      }
*/
      return 'UTC';
    },
    Z: function () { // Timezone offset in seconds (-43200...50400)
      return -jsdate.getTimezoneOffset() * 60;
    },

    // Full Date/Time
    c: function () { // ISO-8601 date.
      return 'Y-m-d\\TH:i:sP'.replace(formatChr, formatChrCb);
    },
    r: function () { // RFC 2822
      return 'D, d M Y H:i:s O'.replace(formatChr, formatChrCb);
    },
    U: function () { // Seconds since UNIX epoch
      return jsdate / 1000 | 0;
    }
  };
  this.date = function (format, timestamp) {
    that = this;
    jsdate = (timestamp === undefined ? new Date() : // Not provided
      (timestamp instanceof Date) ? new Date(timestamp) : // JS Date()
      new Date(timestamp * 1000) // UNIX timestamp (auto-convert to int)
    );
    return format.replace(formatChr, formatChrCb);
  };
  return this.date(format, timestamp);
}

example.php

<?PHP
global $wp_locale;

wp_register_script("date_i18n", self::url . "res/date_i18n.js", null, "2.4.1", true);

$monthNames = array_map(array(&$wp_locale, 'get_month'), range(1, 12));
$monthNamesShort = array_map(array(&$wp_locale, 'get_month_abbrev'), $monthNames);
$dayNames = array_map(array(&$wp_locale, 'get_weekday'), range(0, 6));
$dayNamesShort = array_map(array(&$wp_locale, 'get_weekday_abbrev'), $dayNames);
wp_localize_script("date_i18n", "DATE_I18N", array(
  "month_names" => $monthNames,
  "month_names_short" => $monthNamesShort,
  "day_names" => $dayNames,
  "day_names_short" => $dayNamesShort
));