var date = new Date()
    date.getYear() // 122

Turns out I had to use getFullYear, which is of course perfectly intuitive.

    date.getYear() + "-" + date.getMonth() + "-" + date.getDay()

The actual result for that date is "122-0-2" - not a single component of the date was what I expected.

I'm sure you've read the docs since then but just for the viewers at home:

s/getYear/getFullYear

s/getDay/getDate

getYear is oldfashioned, years since 1900. getDay is day-of-the-week, 0 for Sunday, 1 for Monday, etc

Why, if everything else in JS is 0 indexed? Isn't consistency a good thing in a language? If they'd gone the other way, wouldn't there be people here complaining that 1 indexing is whack?

lol

Even when javascript was written (and likewise with things like perl and php - and of course the underlying function dated back to the 70s ), it was still quite common for people to write dates by hand as 6/6/96 for June 6th 1996, hence people would often write something like

print day() + "/" + mon() + "/" + year()

If you wanted to put a 4 digit year many people

print day() + "/" + mon() + "/19" + year()

After 2000 came round, many sites would claim the year was 19100, I still saw these sites until well into the late 00s

However some people wrote print day() + "/" + mon() + "/" + (1900 + year())

Which would give the correct display.

Changing year() from returning a 2 digit (which in the 80s and even in the 90s was often preferable) to 4 digits would be a breaking change. Changing it to being "the last two digits" rather than "number of years since 1900" would be a breaking change. That's not something that people like to do, hence things like "getFullYear" to return a 4 digit year (or 3 digit for <1000 etc)

This kind of feature[1] lead to many potential Y2K bugs.

[1] Which it shares with Perl and probably many other languages.

  99:  1999
  100: 2000
  …
  122: 2022

On the other hand the much less often used "year of week" would be named "year_of_week()" and hence it is clear to everyone that's not likely what you want.

That would be the sane thing to do. But the same applies to `YYYY`: it should be used for "year of era". But it hasn't been and that's the problem here. For contrast in moment.js, YYYY and yyyy do what you expect and "week year" is GGGG or gggg.

Why? `yyyy` is simpler to type, so makes a lot more sense for "year of era".

> For contrast in moment.js, YYYY and yyyy do what you expect and "week year" is GGGG or gggg.

In LDML (which I assume is what SimpleDateFormat uses), the G field is already spoken for the era name (BC/BCE and AD/CE).

No, the parallel for this would be called `week_year()`, or `iso_week_year()`, to be paired with an `iso_week()` (or `year_week()` since there really is no other formal week-year).

Imagine an API which had methods 'getYear()' and 'GET_YEAR()' where the latter returns the payroll week year, while the former returns the, you know, actual year.

That's what having YYYY produce the week year feels like - a blatant violation of the principle of least surprise.

Which is why your op was saying this is like having an API where year() returns a surprising number thta isn't the year.

You know, like JavaScript does.

There's the part that the entire LDML datetime grammar works like that.

Literally the next letter in your pattern will make it clear: M is the month, and m is the minute.

Which, granted, makes "y" designating the calendar year less than ideal as you'd want to pair Y with M, rather than y with M. Even more so as the 24-hour hour is H, so your standard ISO-8601 pattern is yyyy-MM-ddTHH:mm:ssZ which is... a bit of a mess casing-wise.

> Imagine an API which had methods 'getYear()' and 'GET_YEAR()' where the latter returns the payroll week year, while the former returns the, you know, actual year.

A big difference is the LDML pattern-space is rather more limited, and casing is definitely an important component of it.

> Which is why your op was saying this is like having an API where year() returns a surprising number thta isn't the year.

> You know, like JavaScript does.

If you want to rag on JS's datetime API, which really is Java's, first get in line, second getYear is hardly the worst offender (that belongs to the paired glue-eaters that are getDay and getDate).

But there's a little bit of a difference between mm/MM being minutes/months, where at least as someone thinking about datetime formatting you likely have a concept that the concepts of minutes and months are plausible things 'm' might stand for, vs. yyyy/YYYY where unless you've come across it before, the idea that there might be an inbuilt concept of a 'week year' is likely not going to be something that occurs to you.

I suppose the fact that both 'yyyy/mm/dd' and 'YYYY/MM/DD' produce values that are obviously wrong most of the time should be enough of an incentive for developers to go and look. up the codes. But that said, 'YYYY/MM/DD' produces what looks like the right answer for most of January...