usage-interval.js

const toUnixTime = (date) => date.getTime() / 1000;

const usageInterval = (start, end) => ({
  start: toUnixTime(start),
  end: toUnixTime(end)
});

const getSyndayOfTheWeek = (currentDate) => {
  const date = new Date(currentDate.getFullYear(), currentDate.getMonth(), currentDate.getDate());

  const today = date.getDate();
  const dayOfTheWeek = date.getDay();
  const newDate = date.setDate(today - (dayOfTheWeek || 7));

  return new Date(newDate);
}

const usageIntervalFromPreviousWeek = (today = new Date()) => {
  let currentWeekSunday = getSyndayOfTheWeek(today);
  let previousWeekSunday = new Date(currentWeekSunday);
  previousWeekSunday.setDate(previousWeekSunday.getDate() - 7);

  return usageInterval(previousWeekSunday, currentWeekSunday);
}

module.exports = {
  usageInterval,
  usageIntervalFromPreviousWeek
}

usage-interval.test.js

const {usageIntervalFromPreviousWeek} = require("./usage-interval");

describe("usage-interval", () => {
  it("should return the current week start as interval ending", () => {
    const date = new Date(2021, 8, 25, 10, 15); // 2021-09-25

    expect(usageIntervalFromPreviousWeek(date).end)
      .toBe(new Date(2021, 8, 19).getTime() / 1000);  // 2021-09-19
  });

  it("should return the previews week start as interval start", () => {
    const date = new Date(2021, 8, 25, 10, 15); // 2021-09-25

    expect(usageIntervalFromPreviousWeek(date).start)
      .toBe(new Date(2021, 8, 12).getTime() / 1000);  // 2021-09-12
  });
});