Helper to figure out the schedule for who was responsible to bring out the trash in which week

trashplan.js

const parties = [
  'Herr Freitag',
  'Frau Samstag',
  'WG'
]

console.log(parties.length)

const START_WEEK = 6

const getWeekNumber = (date = new Date()) => {
    // Copy date so don't modify original
    const d = new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate()));
    // Set to nearest Thursday: current date + 4 - current day number
    // Make Sunday's day number 7
    d.setUTCDate(d.getUTCDate() + 4 - (d.getUTCDay()||7));
    // Get first day of year
    var yearStart = new Date(Date.UTC(d.getUTCFullYear(),0,1));
    // Calculate full weeks to nearest Thursday
    var weekNo = Math.ceil(( ( (d - yearStart) / 86400000) + 1)/7);
    // Return array of year and week number
    return weekNo
}

const getResponsibleParty = (parties = ['you'], weekNo = 1) => {
  console.log('weekNo', weekNo)
  const responsibleIndex = Math.floor((weekNo + START_WEEK) / parties.length) - 1
  if (responsibleIndex < 0) {
    return parties.shift()
  }
  console.log('responsibleIndex', responsibleIndex)
  return parties[responsibleIndex]
}

const wasResponsible = getResponsibleParty(parties, 19)
console.log('wasResponsible', wasResponsible)

const currentlyResponsible = getResponsibleParty(parties, getWeekNumber())
console.log('Currently responsible: ', currentlyResponsible)

const nextResponsible = getResponsibleParty(parties, getWeekNumber() + 1)
console.log('nextResponsible', nextResponsible)