function weekInYearFor7Days() {
  const date = new Date(2013, 0, 1);  // January
  const fmt = new DateTimeFormat('w');
  let result = '';
  for (let i = 1; i <= 7; ++i) {
    date.setDate(i);
    result += fmt.format(date);
  }
  return result;
}
Creates a string by concatenating the week number for 7 successive days
@return {string}