@thi.ng/date/units.js

Datetime types, relative dates, math, iterators, composable formatters, locales

import { DAYS_IN_MONTH, DAYS_IN_MONTH_OFFSET } from "./api.js";
import { isLeapYear } from "./checks.js";
const daysInMonth = (year, month) => {
  const days = DAYS_IN_MONTH[month];
  return days + ~~(month === 1 && isLeapYear(year));
};
const dayInYear = (y, m, d) => DAYS_IN_MONTH_OFFSET[m] + d + ~~(m > 1 && isLeapYear(y));
const weekInYear = (y, m, d) => {
  const start = new Date(Date.UTC(y, 0, 1)).getDay() || 7;
  if (!m) {
    if (start === 5 && d < 4) return 53;
    if (start === 6 && d < 3) return 52 + ~~isLeapYear(y - 1);
    if (start === 7 && d < 2) return 52;
  }
  const offset = (start < 5 ? 8 : 15) - start;
  return Math.ceil((dayInYear(y, m, d) - offset) / 7 + 1);
};
export {
  dayInYear,
  daysInMonth,
  weekInYear
};