momentjs - Difference between week of year and week of year ISO tokens (moment.js)

Question

I was studying date formating in moment.js and I came across these tokens: Is there any significant difference between WoY and WoY ISO?

Week of Year

w - 1 2 ... 52 53  
wo - 1st 2nd ... 52nd 53rd  
ww - 01 02 ... 52 53

Week of Year (ISO)

W - 1 2 ... 52 53  
Wo - 1st 2nd ... 52nd 53rd  
WW - 01 02 ... 52 53

Answer 1

According to Wikipedia, the ISO week counter starts the first thursday of the year; so, if the first day of the year is saturday, the first thursday will be in the next week.

Thus, the ISO week of the first thursday will be the first, but the standard week of the first thursday will be the second, e.g.

moment('2005-01-02').isoWeek(); // 53
moment('2005-01-02').week(); // 1
moment('2005-01-03').isoWeek(); // 1
moment('2005-01-03').week(); // 2

Regards!