@technobuddha/library/getOccurrenceInMonth/getOccurrenceInMonth.mjs

A large library of useful functions

import { daysPerWeek } from '../constants';
import getBeginningOfMonth from '../getBeginningOfMonth';
import getDaysInMonth from '../getDaysInMonth';
import addTime from '../addTime';
import modulo from '../modulo';
/**
 * Determine the date of an occurrence of a weekday within a month
 *
 * @param input A date within the month in question
 * @param dayOfWeek The day of the week to find the occurrence
 * @param occurrence The occurrence number, or 'last' to find the last occurrence
 * @param __namedParameters see {@link Options}
 * @defaultValue UTC false
 * @returns A date object corresponding to the occurrence requested, or null if no such date exists in the month
 */
export function getOccurrenceInMonth(input, dayOfWeek, occurrence, { UTC = false } = {}) {
    let day = getBeginningOfMonth(input, { UTC });
    const jump = modulo(dayOfWeek - (UTC ? day.getUTCDay() : day.getDay()), daysPerWeek);
    if (occurrence === 'last')
        return addTime(day, { days: jump + Math.floor((getDaysInMonth(input, { UTC }) - jump - 1) / daysPerWeek) * daysPerWeek });
    else if (occurrence < 1 || occurrence > 5)
        return null;
    day = addTime(day, { days: jump + daysPerWeek * (occurrence - 1) });
    return (UTC ? day.getUTCMonth() === input.getUTCMonth() : day.getMonth() === input.getMonth()) ? day : null;
}
export default getOccurrenceInMonth;