Calendar Matrix (date-fns, ES6) inspired by https://github.com/bclinkinbeard/calendar-matrix

calendar-matrix.js

import getYear from 'date-fns/get_year'
import getMonth from 'date-fns/get_month'
import addDays from 'date-fns/add_days'
import startOfWeek from 'date-fns/start_of_week'

const rows = range(6)
const cols = range(7)

/**
 * Returns a two-dimensional array with calendar represented dates
 */
export default function ({ year, month, weekStartsOn } = {
  year: getYear(new Date()),
  month: getMonth(new Date()),
  weekStartsOn: 0
}) {
  const matrix = []
  const date = new Date(year, month)
  let curDate = startOfWeek(date, { weekStartsOn })

  rows.forEach(row => {
    const week = []
    cols.forEach(col => {
      week.push(curDate)
      curDate = addDays(curDate, 1)
    })

    matrix.push(week)
  })

  return matrix
}

/**
 * Returns an array range from 0 to n
 */
function range (n) {
  return [...Array(n).keys()]
}

import { eachDayOfInterval, endOfWeek, startOfWeek } from 'date-fns'; // 2.2k (gzipped: 989)

function createCalendar(year: number, month: number): Date[] {
  const start = startOfWeek(new Date(year, month, 1), { weekStartsOn: 1 /* Monday */ });
  const end = endOfWeek(new Date(year, month + 1, 1), { weekStartsOn: 1 /* Monday */ });
  return eachDayOfInterval({ start, end });
}

const calendar = createCalendar(2022, 0 /* January */);

console.log(calendar); // Array<Date> between '27 Dec 2021' and '6 Feb 2022'