The JavaScript datetime library is anemic. If you need the current date in the user's locale written in YYYY-MM-DD, use this fun hack:
let currentDate = new Date().toLocaleString("sv").slice(0, 10);
"sv" means Sweden, and in Sweden the locale string is formatted "2023-11-05 00:18:41".
Found this solution on StackOverflow by Tom when making Minecraftle work across timezones.