react-day-picker/src/formatters/formatWeekNumber.ts

Customizable Date Picker for React

import { defaultDateLib } from "../classes/DateLib.js";

/**
 * Formats the week number.
 *
 * @defaultValue The week number as a string, with a leading zero for single-digit numbers.
 * @param weekNumber The week number to format.
 * @param dateLib The date library to use for formatting. Defaults to
 *   `defaultDateLib`.
 * @returns The formatted week number as a string.
 * @group Formatters
 * @see https://daypicker.dev/docs/translation#custom-formatters
 */
export function formatWeekNumber(weekNumber: number, dateLib = defaultDateLib) {
  if (weekNumber < 10) {
    return dateLib.formatNumber(`0${weekNumber.toLocaleString()}`);
  }
  return dateLib.formatNumber(`${weekNumber.toLocaleString()}`);
}