DayJS parses wrong year value for the date "0001-01-01"

Describe the bug When trying to parse the dates “0000-01-01” and “0001-01-01” DayJS returns the years 1900 and 1901 respectively:

const dayjs = require('dayjs')
console.log(dayjs("0001-01-01", "YYYY-MM-DD"))

Output:

d {
  '$L': 'en',
  '$d': 1901-01-01T03:06:28.000Z,
  '$x': {},
  '$y': 1901,
  '$M': 0,
  '$D': 1,
  '$W': 2,
  '$H': 0,
  '$m': 0,
  '$s': 0,
  '$ms': 0
}

Expected behavior The expected behavior is that the returned object has the correct year. Setting the year manually we can see the correct behavior working:

const dayjs = require('dayjs')
console.log(dayjs("2020-01-01", "YYYY-MM-DD").year(1))

Output:

d {
  '$L': 'en',
  '$d': 0001-01-01T03:06:28.000Z,
  '$x': {},
  '$y': 1,
  '$M': 0,
  '$D': 1,
  '$W': 1,
  '$H': 0,
  '$m': 0,
  '$s': 0,
  '$ms': 0
}

Information

• Day.js Version v1.9.6
• OS: Windows
• Browser: N/A (Node.js v12.18.3)
• Time zone: GMT-03:00

[shye0000]

This might be useful

Date - Two digit years map to 1900 – 1999

let date = new Date(98, 1)  // Sun Feb 01 1998 00:00:00 GMT+0000 (GMT)

// Deprecated method; 98 maps to 1998 here as well
date.setYear(98)            // Sun Feb 01 1998 00:00:00 GMT+0000 (GMT)

date.setFullYear(98)        // Sat Feb 01 0098 00:00:00 GMT+0000 (BST)

@iamkun yo, just created a PR to fix this issue in which I refactored a bit the parseDate method using the method setFullYear inspired by @naulacambra

all tests has passed, could you plz review this PR? we really need this fix for our project, thx in advance.

[AHBruns]

So, we just can’t use this with a regular date input without writing a custom guard?

const date = countLeadingZeroes(dateString.split("-")[2] ?? "0000")) === 0 ? dayjs(dateString) : null

Seems pretty annoying considering the whole point of a date lib is to prevent having to parse and manipulate dates manually. Even more so when this is a problem for anyone who parses a date input’s value.