Can't input negative years

[willismonroe]

Describe the bug
I'm trying to work with negative years in a mermaid-js gantt chart but tracing down their date parsing lead me to dayjs. Right now I can get a negative year to display by subtracting years from a positive year date, but there seems to be no way to parse a negative year from the outset.

Expected behavior
I would like to be able to enter dayjs('-2600') and get (NB I don't know if it's a friday) Fri, 01 Jan -2600 00:00:00 GMT.

Information

• Day.js Version: 1.11.10
• OS: Linux
• Browser: Chrome 124

[willismonroe]

I know this is potentially not easy given the Julian/Gregorian change, but it would be very useful!

[klm-turing]

HI @willismonroe ,
I went through your issue and here's what I've come up with so far

dayjs('-2006').toDate() ==> Wed Jan 01 -2600 00:00:00 GMT-0016 (Greenwich Mean Time).

Is this enough for you? Do you have any other use cases you'd like to test?

[willismonroe]

I just tried this on a REPL and got the same result as earlier:

This is version 1.11.10 btw

[willismonroe]

Sorry @klm-turing were you showing the output of a proposed fix? If so, that's great. No other issues I'd like to test at the moment, as I mentioned earlier there are quite a few edge cases extra that would be worth looking into, but even just having negative years is a huge improvement.

[klm-turing]

@willismonroe I wanted to know if it was enough for you first.

I linked a PR 2640. Test it and let me know

[iamkun]

Maybe it will be better to be implemented via a plugin.
IMHO, this might be a project logic, not a common one in dayjs?

[klm-turing]

@iamkun nice touch, I will do that

[klm-turing]

@iamkun The plugin is done, If you have time, Please have a look.