date-fns/getWeeksInMonth.js

import { differenceInCalendarWeeks } from "./differenceInCalendarWeeks.js";
import { lastDayOfMonth } from "./lastDayOfMonth.js";
import { startOfMonth } from "./startOfMonth.js";
import { toDate } from "./toDate.js";

/**
 * The {@link getWeeksInMonth} function options.
 */

/**
 * @name getWeeksInMonth
 * @category Week Helpers
 * @summary Get the number of calendar weeks a month spans.
 *
 * @description
 * Get the number of calendar weeks the month in the given date spans.
 *
 * @param date - The given date
 * @param options - An object with options.
 *
 * @returns The number of calendar weeks
 *
 * @example
 * // How many calendar weeks does February 2015 span?
 * const result = getWeeksInMonth(new Date(2015, 1, 8))
 * //=> 4
 *
 * @example
 * // If the week starts on Monday,
 * // how many calendar weeks does July 2017 span?
 * const result = getWeeksInMonth(new Date(2017, 6, 5), { weekStartsOn: 1 })
 * //=> 6
 */
export function getWeeksInMonth(date, options) {
  const contextDate = toDate(date, options?.in);
  return (
    differenceInCalendarWeeks(
      lastDayOfMonth(contextDate, options),
      startOfMonth(contextDate, options),
      options,
    ) + 1
  );
}

// Fallback for modularized imports:
export default getWeeksInMonth;