lib/jsdom/living/helpers/dates-and-times.js
function weekNumberOfLastDay(year) {
  const jan1 = new Date(year, 0);
  return jan1.getDay() === 4 || (isLeapYear(year) && jan1.getDay() === 3) ? 53 : 52;
}
function weekNumberOfLastDay(year) {
  const jan1 = new Date(year, 0);
  return jan1.getDay() === 4 || (isLeapYear(year) && jan1.getDay() === 3) ? 53 : 52;
}
function weekNumberOfLastDay ( year ) { const jan1 = new Date ( year , 0 ) ; return jan1 . getDay ( ) === 4 || ( isLeapYear ( year ) && jan1 . getDay ( ) === 3 ) ? 53 : 52 ; }
https://html.spec.whatwg.org/multipage/common-microsyntaxes.html#week-number-of-the-last-day https://stackoverflow.com/a/18538272/1937836
https : // html . spec . whatwg . org / multipage / common - microsyntaxes . html#week - number - of - the - last - day https : // stackoverflow . com / a / 18538272 / 1937836