calendrical-javascript

Basic routines in javascript for calendrical computations.

Module architecture

This module uses ES6 module syntax (export / import).

GitHub Page site for software documentation, usage comments, tests and demos

https://louis-aime.github.io/calendrical-javascript/

Purpose

ExtDate object

Extends the built-in Date object, making it possible to specify dates in custom-made calendars. This foreshadows some features of Temporal initiative of Ecma TC39.

Purpose	Date	ExtDate
Number for the first month	0	1
Create date from now	+	+
Create date from timestamp	+	+
Create date from ISO 8601 date expression	+	+
Create date from ISO 8601 date fields	Except in 1st century	All dates
Specify date from date fields of another calendar	0	+
Obtain date fields of another calendar	0	+
Handle week figures	0	+
Obtain real time zone offset in ms	0	+

ExtDateTimeFormat object

Extends Intl.DateTimeFormat. Enables usage of calendars that are not defined in Unicode, and foreshadows some proposed enhancements. ExtDateTimeFormat is called with the same parameters as Intl.DateTimeFormat, plus a calendar object or calendar name. The methods have the same names, but yield more focused results. An additional option eraDisplay is available.

Purpose	Intl.DateTimeFormat	ExtDateTimeFormat
Display or hide era automatically	0	+
Use variants to Unicode's CLDR (using a PLDR)	0	+
Differentiate 2-digit from numeric for time representation	0	+
Customise intercalary month marker for chinese and dangi calendars	0	+

Custom calendars

The general structure of a custom calendar is documented as a type in customcalendarmodel.js module. Some useful examples are given in calendars.js. The calendar of any European country that used the Julian calendar and switched some day to the Gregorian one may easily be specified and used.

Purpose	Unicode	calendrical-javascript
ISO 8601 proleptic Gregorian calendar with algebraic year	0	+
Julian calendar	0	+
Customisable Gregorian calendar with switchover date	0	+
French revolutionary calendar	0	+
Milesian calendar	0	+
Persian calendar (33 years cycle)	+	+

Tentative new week numbering systems are also possible.

timeUnits object (time-units.js)

Convert simple durations to and from milliseconds, using coefficients defined once for all.

Cbcce class (chronos.js)

Define almost any algorithmic calendar with a simple object, see chronos.js or the JSDoc documentation: the Cycle Based Calendar Computation Engine (Cbcce) will convert between timestamp and date-time fields. Basic solid-state integer division and modulo routines are also available. These tools provide a general framework to deal with most algorithmic calendars, including Julian, Gregorian, Coptic, Ethiopic, Meton-cycle implied with the Hebrew calendar, etc. See implementation examples in calendars.js.

WeekClock class (chronos.js)

Define special week rules, with more or less than 7 days, epagomenal days at end of year, or an intercalation day anywhere in the year. The WeekClock instantiated object will compute day sequential number to and from week figures. The rules for the week are specified in an object, see chronos.js or the JSDoc documentation. See implementation examples in calendars.js.

IsoCounter class (chronos.js)

Convert a set of ISO 8601 date fields to and from a sequential day number relative to a given epoch, by default 1970-01-01. Useful for computations on Julian Day, Modified JD, Microsoft base, etc.

fetchDOM promise generator function (fetchdom.js)

Open access to an external XML resource and convert it to a document (DOM) object. This function works like import() but establishes a document object rather than an access to a module. This function is a general purpose object. It is here used to fetch the Private Locale Data Repository (PLDR) used with calendars.

pldr.js

A simplified and stringified version of our Private Locale Data Repository, to be used when the access to the XML PLDR file is not available.

Demonstration and documentation files

The calendrical-*.js and calendrical-demo*.html files are for test and demonstrating purposes. The JSDoc documentation and the demo are available from GitHub Pages. All other *.html files are JSDoc generated files.

calendrical-init.js

An example of initialisation of the complete package. This file may be tailored to specific applications.

calendrical-demo-en.html, calendrical-demo-fr.html

Demonstration pages in English resp. French. They use calendrical-demo.js and calendrical-init.js as script files.

calendrical.demo.js

Event listeners for the calendrical-demo pages. Most global objects of the demo pages are documented as Global by JSDoc.

Calendars used in the demonstration site.

As defined in calendrical-demo.js, some calendars are instantiated from the classes of calendars.js when the page is loaded. Here are their id: :

• iso_8601: the proleptic Gregorian calendar as specified by ISO 8601, with special display order year-month-day, week computations and algebraic year display.
• milesian: the Milesian calendar, as defined at www.calendriermilesien.org; if you use ExtDateTimeFormat, pldr is required.
• prolepgreg: the proleptic Gregorian calendar of common usage: day, month and year as displayed in common way but year is algebraic.
• julian: the julian calendar. You can display date with ExtDateTimeFormat, using CLDR's names for days, months, eras.
• gregorian : you instantiate the GregorianCalendar with a user-defined switching date to Gregorian reckoning. The era field is used to diffentiate "os" (Old Style, meaning Julian reckoning) from "ns" (New Style, Gregorian reckoning). pldr is required, in order to display these eras in a few languages.
• frenchRev: the calendar defined by the French Convention in 1793. pldr is required.
• persian 33: the official algorithmic calendar used in Iran and Afghanistan, based on a 33-years cycle, same effect as Unicode's.