read-gedcom
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Gedcom file reader
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JavaScript
/**
* Convert a Julian day number (JDN) into its corresponding JS date.
* @param jdn The Julian day number
*/
const julianDayNumberToJsDate = (jdn) => {
// Conversion of a Julian day number to a Gregorian date
const j = jdn + 32044;
const cst1 = 146097;
const g = Math.floor(j / cst1);
const dg = j % cst1;
const cst2 = 36524;
const c = Math.floor((Math.floor(dg / cst2) + 1) * 3 / 4);
const dc = dg - c * cst2;
const cst3 = 1461;
const b = Math.floor(dc / cst3);
const db = dc % cst3;
const cst4 = 365;
const a = Math.floor((Math.floor(db / cst4) + 1) * 3 / 4);
const da = db - a * cst4;
const y = g * 400 + c * 100 + b * 4 + a;
const cst5 = 153;
const m = Math.floor((da * 5 + 308) / cst5) - 2;
const d = da - Math.floor((m + 4) * cst5 / 5) + 122;
const cst6 = 12;
const gYear = y - 4800 + Math.floor((m + 2) / cst6);
const gMonth = (m + 2) % cst6; // Starts at 0!
const gDay = d + 1;
return new Date(Date.UTC(gYear, gMonth, gDay));
};
/**
* Converts a parsed Gedcom date to its corresponding JS date (expressed in the Gregorian calendar).
* The supported calendars are: Gregorian, Julian and French Republican.
* The Hebrew calendar is not yet supported. Unknown calendars are inherently unsupported.
* Dual dates will not be converted. BCE dates will be converted assuming the existence of year 0.
* In any of these cases the returned value will be <code>null</code>.
* The argument is assumed to be correct, that is of correct format and valid date.
* This is already guaranteed by {@link parseDate}.
* @param date The parsed date to convert
* @category Parsed value converters
*/
export const toJsDate = (date) => {
var _a, _b;
const day = (_a = date.day) !== null && _a !== void 0 ? _a : 1; // Dirty; if you find a better way to do it, submit PR
const month = (_b = date.month) !== null && _b !== void 0 ? _b : 1;
const year = date.year.isBce ? -date.year.value : date.year.value; // We consider the existence of year 0
if (date.year.isDual) {
return null; // Dual years are unsupported (and rarely ever used anyway)
}
if (date.calendar.isGregorian) {
return new Date(Date.UTC(year, month - 1, day)); // All dates are UTC
}
else if (date.calendar.isFrenchRepublican) {
// We only support dates during which the calendar was in use; i.e. 1<=year<=14
const startYear = 1791;
const isB = year % 4 === 0;
const indices = [21, 21, 20, 20, 19, 18, 20, 19, 19, 18, 18, 17, 16];
const [sYear, sMonth, sDay] = [8, 7, 1];
const index = indices[month - 1] +
(month < 7 && isB ? 1 : 0) +
(year > sYear || (year === sYear && (month > sMonth || (month === sMonth && day >= sDay))) ? 1 : 0);
return new Date(Date.UTC(startYear + year + (month > 4 ? 1 : 0), ((month - 1) + 8) % 12, day + index));
}
else if (date.calendar.isJulian) {
// https://en.wikipedia.org/wiki/Julian_day#Converting_Julian_calendar_date_to_Julian_Day_Number
// Compute the Julian day number (JDN) (this is NOT the modified Julian day number (MJD))
// Only positive values are guaranteed to be valid (i.e. J. years >= -4712)
const isNormal = month > 2;
const y = year - (isNormal ? 0 : 1);
const m = month + (isNormal ? 0 : 12);
const jdn = Math.floor((1461 * y + 6884472) / 4) + Math.floor((153 * m - 457) / 5) + day - 1;
return julianDayNumberToJsDate(jdn);
}
else if (date.calendar.isHebrew) {
return null;
}
else {
return null; // Unsupported calendar kind
}
};
/**
* Converts a parsed Gedcom date and optional time into the corresponding JS datetime.
* @param date The parsed date
* @param time And optional parsed time
* @category Parsed value converters
*/
export const toJsDateTime = (date, time) => {
const dt = new Date(Date.UTC(date.year, date.month - 1, date.day));
if (time != null) {
dt.setUTCHours(time.hours); // Important to remain in UTC
dt.setUTCMinutes(time.minutes);
if (time.seconds !== undefined) {
dt.setUTCSeconds(time.seconds);
if (time.centiseconds !== undefined) {
dt.setUTCMilliseconds(time.centiseconds * 10);
}
}
}
return dt;
};
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