Weekly duty table generator

index.js

import {
  eachWeekOfInterval,
  startOfYear,
  endOfYear,
  endOfWeek,
  format,
  isWithinInterval
} from "date-fns";

const members = [
  { name: "Name1", skip: [new Date("2021.09.09")] },
  { name: "Name2" },
  { name: "Name3" },
  { name: "Name4" }
];
const weeks = {};
const delayedMembers = [];
weeks.begin = eachWeekOfInterval({
  start: startOfYear(new Date()),
  end: endOfYear(new Date())
});
weeks.end = weeks.begin.map((week) => endOfWeek(week));
let memberIdx = 0;

const result = weeks.begin.map((week, index) => {
  let row;
  const start = week;
  const end = weeks.end[index];
  const startFormatted = format(start, "dd.MM.yyyy");
  const endFormatted = format(end, "dd.MM.yyyy");
  const delayedMember = delayedMembers.pop();
  memberIdx = index % members.length;
  let onDuty = delayedMember || members[memberIdx];
  const isWithinWeek = onDuty.skip?.some((day) => {
    return isWithinInterval(day, { start, end });
  });
  if (isWithinWeek) {
    delayedMembers.push(onDuty);
    memberIdx = (index + 1) % members.length;
    onDuty = members[memberIdx];
  }
  row = { date: `${startFormatted} - ${endFormatted}`, duty: onDuty.name };
  return row;
});

console.table(result);