Supporting code for http://www.xaprb.com/blog/2005/12/12/javascript-closures-for-runtime-efficiency/

date-functions.js

/*
 * Copyright (C) 2004 Baron Schwartz <baron at sequent dot org>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published by the
 * Free Software Foundation, version 2.1.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more
 * details.
 */

Date.parseFunctions = {count:0};
Date.parseRegexes = [];
Date.formatFunctions = {count:0};

Date.prototype.dateFormat = function(format) {
    if (Date.formatFunctions[format] == null) {
        Date.createNewFormat(format);
    }
    var func = Date.formatFunctions[format];
    return this[func]();
}

Date.createNewFormat = function(format) {
    var funcName = "format" + Date.formatFunctions.count++;
    Date.formatFunctions[format] = funcName;
    var code = "Date.prototype." + funcName + " = function(){return ";
    var special = false;
    var ch = '';
    for (var i = 0; i < format.length; ++i) {
        ch = format.charAt(i);
        if (!special && ch == "\\") {
            special = true;
        }
        else if (special) {
            special = false;
            code += "'" + String.escape(ch) + "' + ";
        }
        else {
            code += Date.getFormatCode(ch);
        }
    }
    eval(code.substring(0, code.length - 3) + ";}");
}

Date.getFormatCode = function(character) {
    switch (character) {
    case "d":
        return "String.leftPad(this.getDate(), 2, '0') + ";
    case "D":
        return "Date.dayNames[this.getDay()].substring(0, 3) + ";
    case "j":
        return "this.getDate() + ";
    case "l":
        return "Date.dayNames[this.getDay()] + ";
    case "S":
        return "this.getSuffix() + ";
    case "w":
        return "this.getDay() + ";
    case "z":
        return "this.getDayOfYear() + ";
    case "W":
        return "this.getWeekOfYear() + ";
    case "F":
        return "Date.monthNames[this.getMonth()] + ";
    case "m":
        return "String.leftPad(this.getMonth() + 1, 2, '0') + ";
    case "M":
        return "Date.monthNames[this.getMonth()].substring(0, 3) + ";
    case "n":
        return "(this.getMonth() + 1) + ";
    case "t":
        return "this.getDaysInMonth() + ";
    case "L":
        return "(this.isLeapYear() ? 1 : 0) + ";
    case "Y":
        return "this.getFullYear() + ";
    case "y":
        return "('' + this.getFullYear()).substring(2, 4) + ";
    case "a":
        return "(this.getHours() < 12 ? 'am' : 'pm') + ";
    case "A":
        return "(this.getHours() < 12 ? 'AM' : 'PM') + ";
    case "g":
        return "((this.getHours() %12) ? this.getHours() % 12 : 12) + ";
    case "G":
        return "this.getHours() + ";
    case "h":
        return "String.leftPad((this.getHours() %12) ? this.getHours() % 12 : 12, 2, '0') + ";
    case "H":
        return "String.leftPad(this.getHours(), 2, '0') + ";
    case "i":
        return "String.leftPad(this.getMinutes(), 2, '0') + ";
    case "s":
        return "String.leftPad(this.getSeconds(), 2, '0') + ";
    case "O":
        return "this.getGMTOffset() + ";
    case "T":
        return "this.getTimezone() + ";
    case "Z":
        return "(this.getTimezoneOffset() * -60) + ";
    default:
        return "'" + String.escape(character) + "' + ";
    }
}

Date.parseDate = function(input, format) {
    if (Date.parseFunctions[format] == null) {
        Date.createParser(format);
    }
    var func = Date.parseFunctions[format];
    return Date[func](input);
}

Date.createParser = function(format) {
    var funcName = "parse" + Date.parseFunctions.count++;
    var regexNum = Date.parseRegexes.length;
    var currentGroup = 1;
    Date.parseFunctions[format] = funcName;

    var code = "Date." + funcName + " = function(input){\n"
        + "var y = -1, m = -1, d = -1, h = -1, i = -1, s = -1;\n"
        + "var d = new Date();\n"
        + "y = d.getFullYear();\n"
        + "m = d.getMonth();\n"
        + "d = d.getDate();\n"
        + "var results = input.match(Date.parseRegexes[" + regexNum + "]);\n"
        + "if (results && results.length > 0) {"
    var regex = "";

    var special = false;
    var ch = '';
    for (var i = 0; i < format.length; ++i) {
        ch = format.charAt(i);
        if (!special && ch == "\\") {
            special = true;
        }
        else if (special) {
            special = false;
            regex += String.escape(ch);
        }
        else {
            obj = Date.formatCodeToRegex(ch, currentGroup);
            currentGroup += obj.g;
            regex += obj.s;
            if (obj.g && obj.c) {
                code += obj.c;
            }
        }
    }

    code += "if (y > 0 && m >= 0 && d > 0 && h >= 0 && i >= 0 && s >= 0)\n"
        + "{return new Date(y, m, d, h, i, s);}\n"
        + "else if (y > 0 && m >= 0 && d > 0 && h >= 0 && i >= 0)\n"
        + "{return new Date(y, m, d, h, i);}\n"
        + "else if (y > 0 && m >= 0 && d > 0 && h >= 0)\n"
        + "{return new Date(y, m, d, h);}\n"
        + "else if (y > 0 && m >= 0 && d > 0)\n"
        + "{return new Date(y, m, d);}\n"
        + "else if (y > 0 && m >= 0)\n"
        + "{return new Date(y, m);}\n"
        + "else if (y > 0)\n"
        + "{return new Date(y);}\n"
        + "}return null;}";

    Date.parseRegexes[regexNum] = new RegExp("^" + regex + "$");
    eval(code);
}

Date.formatCodeToRegex = function(character, currentGroup) {
    switch (character) {
    case "D":
        return {g:0,
        c:null,
        s:"(?:Sun|Mon|Tue|Wed|Thu|Fri|Sat)"};
    case "j":
    case "d":
        return {g:1,
            c:"d = parseInt(results[" + currentGroup + "], 10);\n",
            s:"(\\d{1,2})"};
    case "l":
        return {g:0,
            c:null,
            s:"(?:" + Date.dayNames.join("|") + ")"};
    case "S":
        return {g:0,
            c:null,
            s:"(?:st|nd|rd|th)"};
    case "w":
        return {g:0,
            c:null,
            s:"\\d"};
    case "z":
        return {g:0,
            c:null,
            s:"(?:\\d{1,3})"};
    case "W":
        return {g:0,
            c:null,
            s:"(?:\\d{2})"};
    case "F":
        return {g:1,
            c:"m = parseInt(Date.monthNumbers[results[" + currentGroup + "].substring(0, 3)], 10);\n",
            s:"(" + Date.monthNames.join("|") + ")"};
    case "M":
        return {g:1,
            c:"m = parseInt(Date.monthNumbers[results[" + currentGroup + "]], 10);\n",
            s:"(Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec)"};
    case "n":
    case "m":
        return {g:1,
            c:"m = parseInt(results[" + currentGroup + "], 10) - 1;\n",
            s:"(\\d{1,2})"};
    case "t":
        return {g:0,
            c:null,
            s:"\\d{1,2}"};
    case "L":
        return {g:0,
            c:null,
            s:"(?:1|0)"};
    case "Y":
        return {g:1,
            c:"y = parseInt(results[" + currentGroup + "], 10);\n",
            s:"(\\d{4})"};
    case "y":
        return {g:1,
            c:"var ty = parseInt(results[" + currentGroup + "], 10);\n"
                + "y = ty > Date.y2kYear ? 1900 + ty : 2000 + ty;\n",
            s:"(\\d{1,2})"};
    case "a":
        return {g:1,
            c:"if (results[" + currentGroup + "] == 'am') {\n"
                + "if (h == 12) { h = 0; }\n"
                + "} else { if (h < 12) { h += 12; }}",
            s:"(am|pm)"};
    case "A":
        return {g:1,
            c:"if (results[" + currentGroup + "] == 'AM') {\n"
                + "if (h == 12) { h = 0; }\n"
                + "} else { if (h < 12) { h += 12; }}",
            s:"(AM|PM)"};
    case "g":
    case "G":
    case "h":
    case "H":
        return {g:1,
            c:"h = parseInt(results[" + currentGroup + "], 10);\n",
            s:"(\\d{1,2})"};
    case "i":
        return {g:1,
            c:"i = parseInt(results[" + currentGroup + "], 10);\n",
            s:"(\\d{2})"};
    case "s":
        return {g:1,
            c:"s = parseInt(results[" + currentGroup + "], 10);\n",
            s:"(\\d{2})"};
    case "O":
        return {g:0,
            c:null,
            s:"[+-]\\d{4}"};
    case "T":
        return {g:0,
            c:null,
            s:"[A-Z]{3}"};
    case "Z":
        return {g:0,
            c:null,
            s:"[+-]\\d{1,5}"};
    default:
        return {g:0,
            c:null,
            s:String.escape(character)};
    }
}

Date.prototype.getTimezone = function() {
    return this.toString().replace(
        /^.*? ([A-Z]{3}) [0-9]{4}.*$/, "$1").replace(
        /^.*?\(([A-Z])[a-z]+ ([A-Z])[a-z]+ ([A-Z])[a-z]+\)$/, "$1$2$3");
}

Date.prototype.getGMTOffset = function() {
    return (this.getTimezoneOffset() > 0 ? "-" : "+")
        + String.leftPad(Math.floor(this.getTimezoneOffset() / 60), 2, "0")
        + String.leftPad(this.getTimezoneOffset() % 60, 2, "0");
}

Date.prototype.getDayOfYear = function() {
    var num = 0;
    Date.daysInMonth[1] = this.isLeapYear() ? 29 : 28;
    for (var i = 0; i < this.getMonth(); ++i) {
        num += Date.daysInMonth[i];
    }
    return num + this.getDate() - 1;
}

Date.prototype.getWeekOfYear = function() {
    // Skip to Thursday of this week
    var now = this.getDayOfYear() + (4 - this.getDay());
    // Find the first Thursday of the year
    var jan1 = new Date(this.getFullYear(), 0, 1);
    var then = (7 - jan1.getDay() + 4);
    document.write(then);
    return String.leftPad(((now - then) / 7) + 1, 2, "0");
}

Date.prototype.isLeapYear = function() {
    var year = this.getFullYear();
    return ((year & 3) == 0 && (year % 100 || (year % 400 == 0 && year)));
}

Date.prototype.getFirstDayOfMonth = function() {
    var day = (this.getDay() - (this.getDate() - 1)) % 7;
    return (day < 0) ? (day + 7) : day;
}

Date.prototype.getLastDayOfMonth = function() {
    var day = (this.getDay() + (Date.daysInMonth[this.getMonth()] - this.getDate())) % 7;
    return (day < 0) ? (day + 7) : day;
}

Date.prototype.getDaysInMonth = function() {
    Date.daysInMonth[1] = this.isLeapYear() ? 29 : 28;
    return Date.daysInMonth[this.getMonth()];
}

Date.prototype.getSuffix = function() {
    switch (this.getDate()) {
        case 1:
        case 21:
        case 31:
            return "st";
        case 2:
        case 22:
            return "nd";
        case 3:
        case 23:
            return "rd";
        default:
            return "th";
    }
}

String.escape = function(string) {
    return string.replace(/('|\\)/g, "\\$1");
}

String.leftPad = function (val, size, ch) {
    var result = new String(val);
    if (ch == null) {
        ch = " ";
    }
    while (result.length < size) {
        result = ch + result;
    }
    return result;
}

Date.daysInMonth = [31,28,31,30,31,30,31,31,30,31,30,31];
Date.monthNames =
   ["January",
    "February",
    "March",
    "April",
    "May",
    "June",
    "July",
    "August",
    "September",
    "October",
    "November",
    "December"];
Date.dayNames =
   ["Sunday",
    "Monday",
    "Tuesday",
    "Wednesday",
    "Thursday",
    "Friday",
    "Saturday"];
Date.y2kYear = 50;
Date.monthNumbers = {
    Jan:0,
    Feb:1,
    Mar:2,
    Apr:3,
    May:4,
    Jun:5,
    Jul:6,
    Aug:7,
    Sep:8,
    Oct:9,
    Nov:10,
    Dec:11};
Date.patterns = {
    ISO8601LongPattern:"Y-m-d H:i:s",
    ISO8601ShortPattern:"Y-m-d",
    ShortDatePattern: "n/j/Y",
    LongDatePattern: "l, F d, Y",
    FullDateTimePattern: "l, F d, Y g:i:s A",
    MonthDayPattern: "F d",
    ShortTimePattern: "g:i A",
    LongTimePattern: "g:i:s A",
    SortableDateTimePattern: "Y-m-d\\TH:i:s",
    UniversalSortableDateTimePattern: "Y-m-d H:i:sO",
    YearMonthPattern: "F, Y"};

The statement document.write(then); taints the output.

Can you remove the dependancy on the eval() function? It isn't allowed on sites with Content Security Policies enabled and is generally considered bad practice

I've created an example that doesn't use eval() here:
https://gist.github.com/kmturley/da90df8b19af500f5f61

Another reworked version without eval + umdification + bowerification can be found here: https://github.com/malko/date-functions

Doing:

Date.parseDate('2018-03-10 12:12', 'Y-m-d H:i')

gives:

Sat Mar 10 2018 12:12:00 GMT+0100 (Paris, Madrid)

How to get the result as Unix timestamp or GMT+0 = UTC time instead @xaprb?

How can I use jQuery for Jalali calendar?
Because when we change language in the calendar with the following label, only the language changes, the dates are displayed according to the Gregorian calendar.
lang: fa