Issue formatting 02/20

[mason-terry]

Describe the bug
const month = dayjs.utc(02/20, 'MM/YY').format('MM')
const year = dayjs.utc(02/20, 'MM/YY').format('YYYY')

The above returns:

month = 03
year = 2020

Expected behavior
month = 02
year = 2020

Additional Information
I think this is a leap year issue

Information

• Day.js Version: v1.8.16
• OS: MacOS 10.14
• Browser Chrome 78
• Time zone: GMT-06:00 DST (Central Daylight Time)

[iamkun]

https://runkit.com/embed/ydhiaf56iwjl

please provide a valid reproduction link

[marc-fisher-q2e]

Odd, just cloning that example I see a different result, no changes.

https://runkit.com/svjard/5dbb2da38795ea001414b056

[mason-terry]

I got the same results as ☝️ "03"

[iamkun]

This is because if no 'day' provided, dayjs will use current 'day'. But we might change it to the first day of the month. And 02-31 -> 03-01.

[iamkun]

fixed in #761 and will use the first day of the month while there's no 'day' provided.