JavaScript Date Formatter

Date.js

/**
 * Date#strftime(format) -> String
 *
 * - format (String): the format string
 *
 * Formats the *date* according to the directives given in the *format*
 * string. Requires a String#interpolate() extension.
 *
 * ## Format Components
 *
 * The format string may contain the following formatting components. Any
 * string not matching the following will simply be passed through:
 *
 *     %a  // The abbreviated weekday name (Sun, Mon, Tue, ...)
 *     %A  // The full weekday  name (Sunday, Monday, Tuesday, ...)
 *     %b  // The abbreviated month name (Jan, Feb, Mar, ...)
 *     %B  // The full month  name (January, February, March, ...)
 *     %d  // Day of the month (1..31)
 *     %dd // Padded day of the month (01..31)
 *     %H  // Hour of the day, 12-hour clock (1..12)
 *     %HH // Padded hour of the day, 12-hour clock (01..12)
 *     %I  // Hour of the day, 24-hour clock (0..23)
 *     %II // Padded hour of the day, 24-hour clock (00..23)
 *     %m  // Month of the year (1..12)
 *     %mm // Padded month of the year (01..12)
 *     %M  // Minute of the hour (0..59)
 *     %MM // Padded minute of the hour (00..59)
 *     %o  // English ordinal suffix for the day of the month (st, nd, rd or th)
 *     %p  // Meridian indicator (am or pm)
 *     %P  // Meridian indicator (AM or PM)
 *     %S  // Second of the minute (0..60)
 *     %SS // Padded second of the minute (00..60)
 *     %w  // Day of the week (Sunday is 0, 0..6)
 *     %y  // Year without a century (00..99)
 *     %Y  // Year with century (2010)
 *     %z  // Time Zone Offset (-4, -6, +10, ...)
 *
 * ## Examples
 *
 * #### "January 1, 2010"
 *
 *     date.strftime("%B %d, %Y")
 *
 * #### "Modified on Tuesday at 4:20 PM"
 *
 *     date.strftime("Modified on %A at %h:%MM %P")
 *
**/
Date.prototype.strftime = function(format)
{
  var formatted,
      ordinals   = {
        1:  "st", 2:  "nd", 3:  "rd", 4:  "th", 5:  "th", 6:  "th", 7:  "th",
        8:  "th", 9:  "th", 10: "th", 11: "th", 12: "th", 13: "th", 14: "th",
        15: "th", 16: "th", 17: "th", 18: "th", 19: "th", 20: "th", 21: "st",
        22: "nd", 23: "rd", 24: "th", 25: "th", 26: "th", 27: "th", 28: "th",
        29: "th", 30: "th", 31: "st" },
      syntax     = /%([A-Za-z]{1,2})/g,
      components = {
        a:  Date.shortDayNames[this.getDay()],
        A:  Date.dayNames[this.getDay()],
        b:  Date.shortMonthNames[this.getMonth()],
        B:  Date.monthNames[this.getMonth()],
        d:  this.getDate(),
        dd: this.getDate() < 10 ? "0" + this.getDate() : this.getDate(),
        H:  this.getHours() % 12 || 12,
        HH: this.getHours() < 10 ? "0" + (this.getHours() % 12 || 12) : (this.getHours() % 12 || 12),
        I:  this.getHours(),
        II: this.getHours() < 10 ? "0" + this.getHours() : this.getHours(),
        m:  this.getMonth() + 1,
        mm: (this.getMonth() + 1) < 10 ? "0" + (this.getMonth() + 1) : (this.getMonth() + 1),
        M:  this.getMinutes(),
        MM: this.getMinutes() < 10 ? "0" + this.getMinutes() : this.getMinutes(),
        o:  "%o", // Pass Through
        p:  this.getHours() >= 12 ? 'pm' : 'am',
        P:  this.getHours() >= 12 ? 'PM' : 'AM',
        S:  this.getSeconds(),
        SS: this.getSeconds() < 10 ? "0" + this.getSeconds() : this.getSeconds(),
        w:  this.getDay(),
        y:  this.getFullYear().toString().substring(2, 4),
        Y:  this.getFullYear(),
        z:  "%z" // Pass Through
      };
  formatted = format.interpolate(components, syntax);
  if (formatted.indexOf("%o") >= 0)
    formatted = formatted.replace("%o", ordinals[this.getDate()]);
  if (formatted.indexOf("%z") >= 0)
    formatted = formatted.replace("%z", (this.getTimezoneOffset() / 60) > 0 ? (this.getTimezoneOffset() / 60) * -1 : "+" + (this.getTimezoneOffset() / 60));
  return formatted;
};

Date.monthNames = [
  'January', 'February', 'March', 'April', 'May', 'June', 'July', 'August',
  'September', 'October', 'November', 'December'
];

Date.shortMonthNames = [
  'Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov',
  'Dec'
];

Date.dayNames = [
  'Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday'
];

Date.shortDayNames = [
  'Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'
];

String.js

/**
 * String#interpolate(values, syntax) -> String
 *
 * Based on String#supplant() by Douglas Crawford:
 *
 *   http://javascript.crockford.com/remedial.html
 *
**/
if (!String.prototype.interpolate)
{
  String.prototype.interpolate = function (values, syntax)
  {
    if (!syntax) syntax = /{([^{}]*)}/g
    return this.replace(syntax,
      function (a, b)
      {
        var r = values[b];
        return typeof r === "string" || typeof r === "number" ? r : a;
      }
    );
  }
}