@burglekitt/gmt/dist/plain/calculate/getWeeksInMonth.js

Temporal-based date and time utilities with timezone support and polyfill integration

import { Temporal } from "@js-temporal/polyfill";
import { getLocaleFirstDayOfWeek, monthGridWeekRow } from "../../internal/index.js";
import { isValidDate } from "../validate/index.js";
/**
 * Return the number of calendar-grid rows (4, 5, or 6) `value`'s month
 * spans, using `locale`'s first day of week.
 *
 * - The count depends on which day the week starts — the same month can
 *   span 4, 5, or 6 rows depending on locale (e.g. February 2026 is 4
 *   rows starting Sunday but 5 rows starting Monday).
 * - Sized the same way `@internationalized/date`'s `getWeeksInMonth`
 *   sizes a datepicker's calendar grid.
 * - Resolves the locale's first day of week via
 *   `Intl.Locale.prototype.weekInfo`.
 * - Returns null if `value` or `locale` is invalid.
 *
 * @param value ISO PlainDate string
 * @param locale BCP 47 locale tag (e.g. "en-US", "fr-FR")
 * @returns number of week-rows the month spans (4-6), or null on invalid input
 *
 * @example getWeeksInMonth("2024-02-15", "en-US") // 5
 * @example getWeeksInMonth("2026-02-15", "en-US") // 4
 * @example getWeeksInMonth("2026-02-15", "en-GB") // 5
 * @example getWeeksInMonth("invalid", "en-US") // null
 */
export function getWeeksInMonth(value, locale) {
    if (!isValidDate(value))
        return null;
    const firstDay = getLocaleFirstDayOfWeek(locale);
    if (firstDay === null)
        return null;
    try {
        const date = Temporal.PlainDate.from(value);
        const firstOfMonth = date.with({ day: 1 });
        return monthGridWeekRow(firstOfMonth, firstDay, date.daysInMonth);
    }
    catch {
        return null;
    }
}