Proposal to use Julian calendar before Sep 14, 1752

[Isaac-D-Cohen]

I'm thinking of writing a patch for the hebcal website which would switch to the Julian calendar for dates prior to September 14, 1752. The main obstacle would be the JavaScript builtin Date class, which uses the Gregorian calendar. Unlike the Go builtin, the JS version actually enforces its Gregorian calendar on you. If you do:

const dt = new Date(0, 1, 29);
d.setFullYear(0);

you get:
0000-03-01T04:56:02.000Z

So switching to the Julian calendar would mean we need to stop using the Date builtin. We can replace it with our own class that doesn't enforce a calendar, but is this too big of a change?

[mjradwin]

Getting rid of Date would be too large of a change for this library which is designed to be very small.

At some point when the new ECMAScript Temporal is widely adopted, we will indeed be able to get rid of Date

const t = Temporal.PlainDate.from({year: 0, month: 2, day: 29});
t.toString(); // '0000-02-29'