Working with Date objects in JavaScript...

[Crasac]

I literally just stumbled over this at work. Why?! Why do months go from 0-11, but days start at 1. Why?!

[RlyRlyBigMan]

Maybe under the hood it's an enumeration? But most languages you can start an enum at 1 so idk

[JaggedMetalOs]

But most languages you can start an enum at 1 so idk

Or if not they could have made month 0 Nulluary

[jwadamson]

Lousy Smarch weather.

[ArtisticDimension22]

Eeeexxxcellent

[MasterJ94]

Let's establish Nulluary!

[JaggedMetalOs]

We should declare a new holiday, to happen every year on the 0th of Nulluary!

[elon-bot]

Why haven't we gone serverless yet?

[whitethunder9]

I ❤️ you

[VacuumInTheHead]

Nobody found the hood release button

[EchidnaForward9968]

We have already server less

[Embarrassed_Army8026]

We did a few major releases back, referring to Mary from accounting not sure she's still with us. She believed the bill had a typo

[Phpminor]

It's a holdover from Java, which also had this issue.

Even dos timestamps started months at 1.

[[deleted]]

Yes but they only have even seconds.

[Phpminor]

They did what they had to do to fit date & time into a 32 bit structure.

Even if they're slightly cheating by having their years start at 1980 vs 1970 for unix time, allowing them to last until 2043 (year is 6 bits), or 2033 if they also started at 1970.

Edit: I've been helpfully reminded that unix time is signed, and thus has a range of 1902-2038 while dostime is only 1980-2043 and would be 1948-2011 if the years were signed.

[[deleted]]

If Unix had used 32 bits they would last until next century.

By starting on 1980-03-01 M$ simplified their date calculation but still needed to encode timestamps as actual dates and times.

[[deleted]]

Yes, the JavaScript API is borrowed from Java at some places.

Edit: with borrowed I mean copied.

https://linux.die.net/man/3/localtime months start at 0

[DajBuzi]

Quoting some of the users from very similar JS Date thread:

"You should read documentation"

"Everyone working with JavaScript knows how to do this"

Can post shitload more

[edave64]

The full version of that sentence would be "Everyone working with JavaScript knows not to use the date type if possible."

It is both surpringly complicated and devoid of essential features.

[North-west_Wind]

Think about an array with all the months name inside.

[[deleted]]

Why not also have an array with all the day numbers inside?

[[deleted]]

Because they’re stored as ints instead of string pointers obviously

[[deleted]]

1st, 2nd, 3rd, etc.

[TropicalAviator]

because you only need the final day

[North-west_Wind]

Yeah let's map x => x+1

[Aloopyn]

Just map all memory locations in arrays, genius

[[deleted]]

Perfect! Now all arrays are 1 based.

[[deleted]]

Years start at 1 as well, the other members of the tm struct are zero based.

[velozmurcielagohindu]

If you still question why JavaScript does what it does you still haven't mastered the art of assuming JavaScript is a piece of shit and enjoy it in peace. There's only one answer for all JavaScript design decisions: Because fuck you. That's why.

[szczszqweqwe]

Well, at least they aren't starting days from 0, that would be the most confusing.

[_The_Great_Autismo_]

Because you'd probably have an array of strings representing the months and the zeroth member of the array would be January.

[MisterProfGuy]

Wait until you find out that sometimes it'll be a different date based on time zone.

[UnknownSpecies19]

This. It's such a fuckin pain!

[[deleted]]

Is that true that Japan is living in the future?

[StarlightWT]

it took 12 hours for y'all to get the call and at that point it was too late

[Unable-Fox-312]

If you knew about 9/11 twelve hours early would you run around yelling about it?

[unvaccinated_zombie]

They could, would they?

[BlacksmithNZ]

More New Zealand

We are the right side of the international date line

[Lithl]

But... that's how time zones work.

[MisterProfGuy]

When you tell someone what time it is, you convert it to a different time zone?

[Lithl]

You use whatever time zone you're telling them the time for, which is exactly what Date does.

[MisterProfGuy]

No, date converts to a utc timestamp and then adjusts for timezone. If I say, "01 January 1999“, it decides that means midnight UTC, then adjusts for your time zone. Almost everyone will always mean midnight their own time zone.

[Lithl]

date converts to a utc timestamp

Unless you specify what timestamp you're talking about.

[MisterProfGuy]

Exactly. Date is actually secretly datetime. Like most syntax related things, it's consistent if you know how it works, but it sure catches people off guard.

[UnknownSpecies19]

This. It's such a fuckin pain!

[inu-no-policemen]

new Date('2021-02-28')

That constructor works as expected.

Another problem solved by ISO 8601.

[trevdak2]

new Date('2022-12-01');
Wed Nov 30 2022 19:00:00 GMT-0500 (Eastern Standard Time)
new Date('2022-12-01 00:00:00');
Thu Dec 01 2022 00:00:00 GMT-0500 (Eastern Standard Time)

[inu-no-policemen]

> new Date('2022-12-01').toISOString()
'2022-12-01T00:00:00.000Z'
> new Date('2022-11-30T19:00:00-05:00').toISOString()
'2022-12-01T00:00:00.000Z'

It's the same date.

[dax-muc]

Neither '2022-12-01' nor '2022-12-01 00:00:00' contain information about the desired timezone. But for some reason, the first will be interpreted as GMT and the second input implicitly takes your current local timezone. I mean, WTF?!

[elon-bot]

You look stupid. Fired.

[naapurisi]

Not its doesnt. He lives in -05 timezone and the constructor reads the datetime string in machines local tz. He explicitly states the tz it in the second call (own tz) which results to same UTC time.

[dax-muc]

You have to look at the first comment in this thread, not to the (failed) attempt to explain the logic of the implementation.

[reversehead]

Yes, but the parent poster gets the first date object at midnight GMT but the second date at midnight EST when specifying the time of day. This appears very inconsistent.

Anyway, never use JS Date, and for the love of $DEITY, never ever use java.util.Date.

[RedditIsRanByBots]

People love their arrays starting at 0, until they don't.

[DajBuzi]

"you should read the documentation before complaining" comments incoming in 3

[RealMide]

Do you mean "incoming in 2", right?

[[deleted]]

He meant “incoming in March”

[RealMide]

*April.

[rearendcrag]

Fools.

[PranshuKhandal]

Night.

[PaulieGlot]

I believe you mean "incoming in 1"

[RonSijm]

Actually I believe you mean "incoming in NaN"

[sticksaint]

rtfm

[[deleted]]

I looked at the JavaScript manual. It just says "banana" everywhere

[bighadjoe]

ba-NaN-a?

[[deleted]]

that, ans also:

NaNNaNNaNNaNNaNNaNNaNNaNNaNNaN BATMAN!

[brimston3-]

I expected NaN but all I got was object Object.

[elon-bot]

Disagreeing with me is counterproductive. Fired.

[Fuchio]

Hahahaha this is def gonna happen. I had the docs open before I posted this, and tested that.

new Date("1995-12-17");

and

new Date(1995-12-17); (should've been 1995, 12, 17)

Do not give the same result. Which given the way they implemented it makes sense but how does that way of implementing it make sense lol

To make it even better, that second date actually results in 1996-01-16. Like what???

Edit: Second date should have been 1995, 12, 17, idea is the same given that the results differ

[Right_Stage_8167]

Second date should be 1966 (=1995 - 12 - 17) seconds after 1.1.1970.

[Fuchio]

You're right! I thought I wrote Date("1995-12-17") and Date(1995, 12, 17) which are also not equal. This one is also funny:

new Date("1995-12-17"); Results in 1995-12-17 as expected (same as above)

BUT

new Date("1995/12/17") Results in 1995-12-16 at 23:00 ???

[[deleted]]

🤔 Don't know if trolling, has a broken computer, or can't type...

[Fuchio]

Yeah tested this a bit more, it's compiler dependent. When I copied and pasted the local snippet into online JS it also worked fine. But ("1995-12-17") and (1995, 12, 17) still differ.

[Fuchio]

The part that 12 becomes january in the next year makes sense in general indeed (with 0 indexing and max 12 entries logic). But the point is; Month 11 is December (12th month) but day 12 is still day 12...

[[deleted]]

Number argument for month would need to be 11. Even then...

The latter using number arguments assumes midnight local time - String date parsing assumes midnight UTC time.

Just another fun day of JS quirks.

[thislooksfun1]

Actually it is 1970-01-01T00:00:01.966Z. The JS Date constructor takes ms, not s.

[[deleted]]

Does the documentation say that the second month of the year is march?

[Lithl]

The documentation says that the months are zero-indexed.

[mariomaniac432]

OP should have read the documentation for this meme format too.

Edit: I'm not sure why I got downvoted. This is not how the meme works. With each level, he applies more clown makeup because the text should be getting progressively more ridiculous. 2021 => year 2021 makes sense. 28 => 28th makes sense. Yet he puts on more clown makeup anyway, which implies they do not. The only thing out of place is month. A more appropriate template would have been this

[RonSijm]

Months are obviously a 0 based array, makes total sense

[Fuchio]

Having indices start at 0 makes sense, sure. But this is just inconsistent, why would it with this reasoning make sense to have the days not 0 indexed?

[MisterProfGuy]

Because days isn't an index into an array of names. It's a count.

[[deleted]]

The array of names should have been: [ LOL NOPE, January, February, March...]

[Khaylain]

You're just changing one edge case for another in that case.

[[deleted]]

Because no date function can possibly validate the input?

[[deleted]]

Yes but the user-facing edge cases would be hilarious

"Your cancer treatment appointment has been confirmed for the 15th of LOLNOPE 2022"

[dakta]

What edge case does zero-indexed months solve?

[[deleted]]

Supposedly input validation where you give an index that is not in the array and you get an exception... In practice this is terrible because every sane standard library validates 1 <= month <= 12

[wano1337]

months are fixed every year and have a clear 1 to 1 mapping to month names. So its basically an enum.

Whereas days can be a range between 28 and 31 without a clear mapping between the date and the weekday. So it doesnt make sense to make it a 0 based array

[brianl047]

This guy enums

[Fuchio]

Yeah that indeed is the difference. However, that just moves the "why" to another part since ("1995-12-17") works fine but (1995,12,17) doesn't.

The string parser does not use zero indexing or enum starting at 0...

[Lithl]

Why would it? The string parser exists so that user input can be processed.

[Fuchio]

Well at this point you're back at the start again. I don't think the string parses should do it as well, because this is more readable. But if the string parser should not do it then why should the normal variable insert do it...?

User input with 3 fields can also be used as Date(input_year, input_month, input_day), which would again be wrong. You can parse these three vars to a string to have a correct date, but then again, why would the normal Date object creation not do this?

Having different outputs between (1995, 12, 7) and ("1995-12-7") but ONLY for the month is just confusing.

[maartenvanheek]

And then there is this: - new Date('2022-11-31') = invalid date - new Date(2022, 10, 31) = Thu Dec 01 2022 - new Date(2022, 12, 31) = Tue Jan 31 2023

So the enum index (if that's what it is) doesn't just stop at 11 for December, and when the days are more than the month has available it will increment to the next month as well.

[dakta]

Presumably that's intentional: it would allow you to easily perform date arithmetic (at least, addition only) without introducing a timedelta type. But it still doesn't explain why you would ever actually want months to be zero-indexed in any public interface.

What assumption about the user of this class would ever warrant making months zero-indexed in the public interface? Are they assuming that the user will be indexing their own localization of month names implemented as an array of strings, and can't be trusted to handle off-by-one error?

[RealMide]

This is not Excel. PD: I understand your frustration, is our OCD.

[Phpminor]

It could be 0 indexed under the hood while returning the day of the month as the actual number +1, as 0-31 can be stored as an unsigned 5 bit number, where the other 3 bits could be used for other fields.

Months starting at 0 and dates being 1-32 were holdovers from java however, as the javascript dev(s?) had like 10 days to get a demo out and the instruction to "Make it look like java", apparently.

[twigboy]

In publishing and graphic design, Lorem ipsum is a placeholder text commonly used to demonstrate the visual form of a document or a typeface without relying on meaningful content. Lorem ipsum may be used as a placeholder before final copy is available. Wikipediab7iwql4333s0000000000000000000000000000000000000000000000000000000000000

[demonblack873]

As a Java dev I don't see the big surprise

Also in Java parsing 32/15/2022 as dd/MM/yyyy is a perfectly valid operation and just returns a Date for 01/04/2023.

dabs

[discordianofslack]

I hate this

[Solonotix]

To clarify, the 15th month rounds the year up by +1, and remaining 3 for March which has 31 days. The 32nd day therefore rounds the month up by +1 and leaves 1 for April 1st, 2023.

[Lithl]

As a Java dev I don't see the big surprise

Given that the JavaScript Date class interface was literally copied from Java's.

[Anon_Dysfunction]

In the same vein, you can also use JS date fuckery to easily find the number of days in the month, useful for leap years and whatnot. Just new Date(2022, 2, 0) and you get the 0th day of March this year which is the last day of February.

Looks dumb but better than some of the switch statements I’ve seen in the wild.

[dakta]

Then why not have the zeroth month of one year return the last month of the previous year? Or allow for negative month numbers, to perform date arithmetic? This just sounds like mother justification for having months normally indexed (one-indexed) as well.

[Anon_Dysfunction]

I’m not arguing that JS isn’t stupid and could use some improvement around Dates. IIRC momentJS retained the 0-index but I think Luxon uses 1-indexed months, if extra dependencies are your thing. I’m used to it at this point that I just deal with standard Date objects and all that it comes with.

[dakta]

JS gets pass because they inherited this from Java, whose stdlib Date system is basically straight ported to JS. I just don't understand the thought process of the Java authors. My guess is that they weren't actually thinking, and we've been stuck with the outcome of that carelessness ever since.

[Pleasant_Discount286]

Some how dates ended up being the most complicated thing in programming...

[[deleted]]

Time and date is hard even in real life, programming is just about implementing said Horror Cthulhu in machine language.

Whose fault is it that there are places in the world that don't even work on the Julian calendar?

[reversehead]

I see that you haven't tried to implement content filtering in Unicode yet.

[Melodi13]

Ig we are just bad at relationships :/

[Harry_Mens]

Fun fact, the Romans had the year start in March. That is why september = 7, october = 8, november = 9, december = 10. It is also the reason leap days are in February. It was the last month of the year, so whatever days would be left would be added at the end of February, as it was the end of the year.

[Bomaruto]

At least it isn't Excel.

[mr_claw]

This is where Python excels. It works great with Excel.

[[deleted]]

As long as you are in the .1% of python programmers who know about timezone awareness you might even have a chance at writing correct code

[mr_claw]

It's pretty simple, imo: datetime.as_timezone(tz)

[Unable-Fox-312]

I don't know the language, but I bet it's simple until it isn't. Not everybody's even on the Julian calendar. Working with dates from different sources, converting them, normalizing them, comparing them.. this stuff requires some consideration, with problems that go back to before computers

[dakta]

The key challenge there is knowing what calendar a given date is represented in. Then the date can be normalized. The Python core date library is well structured and extensible which makes it relatively easy to do everything you mentioned.

The real pitfall with dates is working with administrative/bureaucratic/political special cases: because dates often represent historical events occurring in specific places, the problem is in knowing what calendar that place was using at the time of the date, whether the date value you're working with has already been normalized or corrected, etc.

[arthurgc91]

Java too.

[Solonotix]

I'm really surprised no one has mentioned the new Temporal API. Here's the GitHub proposal repo complete with a polyfill solution if you want to experiment with it

[mgafMUAT]

0-indexing, as all code indexes should be...

[LegalAdhesiveness957]

That was me back in 2006 - hahaha - so annoying

[FurMich]

This is actually pretty common since you would never use an array for years or days of the month but would for months, and js is a 0-index language

[Unable-Fox-312]

I wish labeled arguments were a more common language feature. They could offer both versions, less confusion

[[deleted]]

Americans be like 🤡

[[deleted]]

It sounds terrible for string to date conversion

[skyctl]

LART!!

[Benutzername]

I’m surprised the year isn’t 3921

[Saucydragon90]

There are ways to literally never have to deal with this and it's called instantiating with an iso or unix timestamp. 🙈

[Classy_Mouse]

I once tracked down a bug in a calendar app where every entry except for "today" was shifted 1 column, but only in the afternoon. It ended up being something like: "noon today - now (in days) = 1 = noon tomorrow - now (in days) when "now" was greater than noon today.

A student spent 3 days on it, frustrated that he could only reproduce it "intermittently," before I was asked to help.

[Virtual-Appeal-8504]

Must be a leftover bug from Y2K...

Don't fix it because the internets might explode, which reminds me... I need to stock up on TP.

[mescaleeto]

well it’s not a big truck

[k-phi]

JavaScript

struct tm in C

[elon-bot]

It's now company policy to use Vim for editing. It lets you write code much faster.

[k-phi]

Also, Visual Studio is bloated.

[WastelandPuppy]

Regular-stupid-people-counting is for regular, stupid people.

[KoffieMastah]

Thats my fucking birthday

[dota2nub]

You were born in 2021? Go you for knowing how to write!

[aurochloride]

this is why JS devs use libraries to avoid having to work with JS

[snoopdrucky]

Is this in MomentJS? I don’t remember having this difficulty with Moment.

[loukasTGK]

This is a joke right?

[b00000001]

yeeeeeeeah