convert date to Year +  Week number and return this as Number yyyycc (always 6 digits)

 

example:

alert(Date(2021,01,12).toYearWeek()) // return 202102 as number, if calendar system is ISO-8601

 

The system is using the company calender settings for calculate the first day of week

if calendar system not defined, it return the first day of week related to ISO-8601