weekOfYear week method doesn't seems to handle week number 53 for 'fr' locale

[4rno]

Describe the bug
I have an issue with the dayjs week() method compared with the moment.js one.
My issue is probably linked to this one #772

Expected behavior
I tried with that date: 2020-12-31, which is supposed to be a day in the week number 53. (if i refer to this http://www.whatweekisit.org/ or any french calendar).

Here is an example of what moment.js week() method return for 'fr' and 'en-gb' locales: https://runkit.com/4rno/5f05ee0eef35c50013368d1b
moment.js returns week 53. Which is correct

But, I have different results with dayjs: https://runkit.com/4rno/5f05ebfc841930001389a53e
In 'fr' locale, it returns week number 1. But in 'en-gb' locale, it returns correctly week 53.

It seems to be linked with the parameter yearStart in locale config files. But i don't know exactly how it is supposed to work.
Or maybe i'm wrong somewhere.

Information

• Day.js Version v1.8.29
• OS: [Mac OS]
• Browser [Chrome 83]
• Time zone: [CET]

[iamkun]

Thanks, Update French (fr) locale to set correct yearStart config.

[iamkun]

🎉 This issue has been resolved in version 1.8.30 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[flomoto]

Same problem in german locale. 4 january needs to be week 1, not 2.

[niklasHagner]

Just wanted to let you know I was having this issue too while using dayjs version 1.10.4 but after upgrading to 10.10.7 it's resolved. ✅

So the latest version as of today works as expected.
But thought I'd write here anyway cause this thread suggest it was fixed as early as version 1.8.30 , and that wasn't the case for me. At least not with my setup of multiple plugins

The code I was using

var dayjs = require('dayjs')
var isToday = require('dayjs/plugin/isToday')
var weekOfYear = require('dayjs/plugin/weekOfYear')
var utc = require('dayjs/plugin/utc') 
var timezone = require('dayjs/plugin/timezone')
const { months } = require('dayjs/locale/sv')
dayjs.extend(isToday)
dayjs.extend(weekOfYear)
dayjs.extend(utc)
dayjs.extend(timezone)
dayjs.tz.setDefault("Sweden/Stockholm")
require('dayjs/locale/sv')
dayjs.locale('sv')

//Test scenario
var firstDayOf2021 = dayjs("2021-01-01");
console.log("weekNumber:", firstDayOf2021.week()); //With version version 1.10.4 it'll incorrectly output week1, with 1.10.7 it'll correctly output week53