startOf('week') and startOf('isoWeek') not expected result

[dominictobias]

Describe the bug
Hi there seem to be two bugs relating to this feature:

1. start of week (non ISO) starts on Saturday instead of Sunday
2. there seems to be no support for isoWeek

Expected behavior
Here is the expected value in moment vs what we get in dayjs:

https://codesandbox.io/s/dayjs-unexpected-startof-week-syph3

I'm aware there is a dayjs-plugin-utc plugin. All the same using utc() has no effect on the issue except that it makes week incorrectly get set to Sunday instead of Monday (looks like week is one day out either way). Does dayjs not intend to have any ISO stuff in the core? Thanks

Information

• Day.js Version [e.g. v1.0.0] - 1.8.16
• Time zone: GMT+0100 (British Summer Time)

[iamkun]

1 we have our official utc plugin
2 isoWeek is not supported at the moment

[dominictobias]

Ok thanks didn’t realise I wasn’t using the official one

[iamkun]

add support isoWeek #811

Check isoWeek here https://day.js.org/docs/en/get-set/iso-week