Simple Yahrzeit calculator using Hebcal package

.gitignore.yahrzeit

# Ignore things not in the gist
*
!facade.js
!hebcal.js
!README.md
!temporal.js
!why.png

README.md

Exploring Temporal API with Yahrzeit conversion

• hebcal.js: uses hebcal package from npm (GPL v3).
• temporal.js: uses proposal-temporal from TC-39 proposal (MIT)
  • facade.js: implements Temporal.Calendar using hebcal (GPL v3).

Installation

# Bootstrap example
git clone git@gist.github.com:8f36e36afabfff2c28eb706aa7011dd0.git yahrzeit
cd yahrzeit
mv .gitignore.yahrzeit .gitignore
npm install hebcal proposal-temporal

# Run hebcal-based conversion
node ./hebcal.js 

# Run proposal-temporal based conversion using
# a specified Temporal.Calendar-compliant API
CALENDAR_FACADE_PATH='./facade.js' node ./temporal.js

Why?

facade.js

/**
 *
 * As per [Hebcal License](https://github.com/hebcal/hebcal-js/blob/master/COPYING)
 * the code in this file is provided under the terms of GNU General Public License v3.0
 *
 */

const Hebcal = require('hebcal');
const { Temporal, Intl } = require('proposal-temporal');

module.exports = class HebrewCalendar extends Temporal.Calendar {
  constructor() {
    super();
  }
}

hebcal.js

/**
 *
 * As per [Hebcal License](https://github.com/hebcal/hebcal-js/blob/master/COPYING)
 * the code in this file is provided under the terms of GNU General Public License v3.0
 *
 */

const Hebcal = require('hebcal');

function observeOn(d, conj = '<––>') {
  return `${d.year}/${d.month}/${d.day} ${conj} ${d.greg().toDateString()}`;
}

function getYahrzeitDates(hdate, futureYears = 10) {
  const iter = new Hebcal.HDate(hdate);

  const honor = iter.year;
  return [...Array(futureYears + 1).keys()]
    .slice(1)
    .map(away => {
      iter.setFullYear(honor + away);
      return new Hebcal.HDate(iter);
    });
}

function remember(then, futureYears) {
  const yahrzeits = getYahrzeitDates(then, futureYears);
  return [
    `🕯 Remembering ${observeOn(then)}`,
    ...yahrzeits.map((remember, away) => {
        return `🕐 [+${away + 1}] ${observeOn(remember, 'should be remembered on')}`;
      })
  ];
}

//
// A Jewish individual who is mourning the loss of a loved one typically sits
// shiva.In Judaism, you are considered a mourner when your spouse, mother,
// father, brother, sister or child passes away.Often, other relatives also
// “sit shiva” and mourn with you
//
const remembered = [
  remember(new Hebcal.HDate(new Date(2009, 02, 03)), 20),
  remember(new Hebcal.HDate(new Date(2016, 06, 02))),
  remember(new Hebcal.HDate(new Date(2021, 01, 18)))
];

console.log(
  remembered
    .map(r => r.join('\n'))
    .join('\n\n')
);

temporal.js

/**
 *
 * (C) Charlie Robbins, 2020
 * LICENSE: MIT
 *
 */

const { Temporal, Intl } = require('proposal-temporal');
const HebrewCalendar = require(process.env.CALENDAR_FACADE_PATH);

function observeOn(greg, conj = '<––>') {
  //
  // n.b. this will throw until `facade.js` is fully
  // implemented
  //
  const heb = greg.withCalendar('hebrew')

  return `${heb.toDateString()} ${conj} ${d.greg().toDateString()}`;
}

const then = Temporal.Date.from('2016-07-02');
console.log(`🕯 Remembering ${observeOn(then)}`);

const yahrzeitDates = getYahrzeitDates(then)
  .forEach((remember, away) => {
    console.log(`🕐 [+${away}] ${observeOn(remember, 'should be remembered on')}`);
  });