How to calculate current week number?

Question

JavaScript

I ask for help,
how can I calculate the week number for a specified date, there is numweek, but I wanted to know what other options are there)))

Answer 1

mathematically (without taking into account the days of the week), the seven-day number = int((N+6)/7),
where N is the ordinal number of the day in the year,
int() is the discarding of the fractional part of the number.
But we need to agree on where to start counting the first week.
For example, January 1, Saturday. There are options (in Britain, the week starts on Sunday):
1 - 1st week, 2-8 - 2nd week, ..
1 - 0th week (because it is incomplete), 2-8 - 1st week, ..
1.2 - 1st week, 3-9 - 2nd week,..
1.2 - 0th week (because incomplete), 3-9 - 1st week,..