date-fns/esm/getWeekOfMonth/index.js

Modern JavaScript date utility library

import getDate from "../getDate/index.js";
import getDay from "../getDay/index.js";
import startOfMonth from "../startOfMonth/index.js";
import toInteger from "../_lib/toInteger/index.js";
import requiredArgs from "../_lib/requiredArgs/index.js";
/**
 * @name getWeekOfMonth
 * @category Week Helpers
 * @summary Get the week of the month of the given date.
 *
 * @description
 * Get the week of the month of the given date.
 *
 * ### v2.0.0 breaking changes:
 *
 * - [Changes that are common for the whole library](https://github.com/date-fns/date-fns/blob/master/docs/upgradeGuide.md#Common-Changes).
 *
 * @param {Date|Number} date - the given date
 * @param {Object} [options] - an object with options.
 * @param {Locale} [options.locale=defaultLocale] - the locale object. See [Locale]{@link https://date-fns.org/docs/Locale}
 * @param {0|1|2|3|4|5|6} [options.weekStartsOn=0] - the index of the first day of the week (0 - Sunday)
 * @returns {Number} the week of month
 * @throws {TypeError} 1 argument required
 * @throws {RangeError} `options.weekStartsOn` must be between 0 and 6
 *
 * @example
 * // Which week of the month is 9 November 2017?
 * var result = getWeekOfMonth(new Date(2017, 10, 9))
 * //=> 2
 */

export default function getWeekOfMonth(date, dirtyOptions) {
  requiredArgs(1, arguments);
  var options = dirtyOptions || {};
  var locale = options.locale;
  var localeWeekStartsOn = locale && locale.options && locale.options.weekStartsOn;
  var defaultWeekStartsOn = localeWeekStartsOn == null ? 0 : toInteger(localeWeekStartsOn);
  var weekStartsOn = options.weekStartsOn == null ? defaultWeekStartsOn : toInteger(options.weekStartsOn); // Test if weekStartsOn is between 0 and 6 _and_ is not NaN

  if (!(weekStartsOn >= 0 && weekStartsOn <= 6)) {
    throw new RangeError('weekStartsOn must be between 0 and 6 inclusively');
  }

  var currentDayOfMonth = getDate(date);

  if (isNaN(currentDayOfMonth)) {
    return currentDayOfMonth;
  }

  var startWeekDay = getDay(startOfMonth(date));
  var lastDayOfFirstWeek = 0;

  if (startWeekDay >= weekStartsOn) {
    lastDayOfFirstWeek = weekStartsOn + 7 - startWeekDay;
  } else {
    lastDayOfFirstWeek = weekStartsOn - startWeekDay;
  }

  var weekNumber = 1;

  if (currentDayOfMonth > lastDayOfFirstWeek) {
    var remainingDaysAfterFirstWeek = currentDayOfMonth - lastDayOfFirstWeek;
    weekNumber = weekNumber + Math.ceil(remainingDaysAfterFirstWeek / 7);
  }

  return weekNumber;
}