Welcome to the wonderful world of code obfuscation

As a Real Programmer(tm) I have developed such a deep fear of anything time and date related that I would fully endorse dispatching an API call to the tz_database instead of attempting any fucking part of this.

Kids, it's fine to meme about silly stuff... but date and time is deadly serious, regardless of how careful you think you're being you are wrong.

Do you know how many timezones there are in Indiana? No? Look it up and scream in horror.

What if I told you that weekend days are locale dependent?!

Time and date is the black hole where optimistic programmers go to die. Nothing is simply with localisation and if you think it is, you mustn’t have worked enough with it.

Source: Run a system that schedules millions of interactions across the world and deeply depend on this. The amount of code to manage and/or call out to external services to give us information about time zones, summer time, locale specific settings, day names, calendar systems, week numbers etc etc.
Here's a fun thought experiment: What gregorian year and date will the spacian date value of zero correlate to? Trick question.

The atomic clock on the moon and every other celestial body colonized will simply start at zero, and thanks to relativity it will not actually be the same rate of time passing as on earth.

Enjoy your nightmares.
Luckily we won't colonize the moon or another planet anytime soon...
- What gregorian year and date will the spacian date value of zero correlate to? Trick question.
  
  The atomic clock on the moon will simply start at zero, and thanks to relativity it will not actually be the same rate of time passing as on earth.
  
  Enjoy your nightmares.
IMO every datetime should be in utc, and variables for datetimes should either be suffixed "Utc" or have a type indicating their time zone (DateTimeOffset or UtcDateTime etc). Conversion to local time happens at the last possible second (e.g. in the view model or an outbound http request parameter). Of course that doesn't solve the problem of interoperating with other ~~morons~~ programmers who don't follow these rules, but it keeps things a lot neater locally.

Scheduling based on regional time conventions (holidays, weekends, etc) is just not great though.
- Throwing UTC everywhere doesn't solve comparisons around leap seconds. I'm sure they're other issues with this method, but this is kinda the point of "just use a library". Then it's someone else's problem.
2 timezones but the complication is that it is dependent on which country you're in?
- There are two distinct time offsets used in Indiana but there are 11 different timezones https://en.m.wikipedia.org/wiki/Time_in_Indiana
Relevant talk by Jon Skeet

https://invidious.io.lol/watch?v=64X8rCy1jSA

You want to expand your business to Europe. Bam, your code is broken, in Europe the week starts on Monday.

Than you want to expand to the middle east. Bam, broken again... Because in arab countries and Israel, the weekend is on Friday and Saturday.

Then you want to expand to Mexico and India. Bam, broken again, their weekend is only on Sunday.

The obvious solution is to inject an IWeekendDaysOfWeekProvider service in the inversion of control container. In your, uh, javascript web app.
- Just npm install isWeekend for the required locales.
  
  Depends on: isMonday, isTuesday,...
- This but non-ironically.
Not using CultureInfo.InvariantCulture for basically everything
This dude(ette) globalizes.
I was wondering why the second example returned monday and tuesday. I had no idea the week could start any day other than monday

Honestly the first one is the only one that works when people define the first day of the week differently. On the other hand, it does make you wonder. If Sunday is the first day of the week (as it is in many places) then how is it also part of the weekend?

But if you're worried about locale, you can't assume people use the string "Saturday" to describe Saturday either. That solution only works in English.
- I assume this is in a language where the first day of the week is a fixed part of the language (like JS).
Yeah it's the front end of the week and Saturday is the rear end
They're the week's ends, front and back.
- Thats not really one weekend then though, is it? Its more like last week’s post-week weekend and this week’s pre-week weekend

Why would you call it weekend and the start the week with half of it?!

A rope has two ends, and so does a week
- Sentences have both meanings and sound, yours have sound
- Do you say weekend or weekends?
- So, where does it start then?
- Three-day workweek now

Ok another US local units are retarded rant: it's called weekEND! why do you start your week at sunday and not monday! Sunday is part of the weekEND!

If you're referring to an "end" of an object, it can refer to the extreme of a side of it. For example, aglets are at either end of a shoelace.
- I'm refering to end in a temporal sense because we are talking about a time context here. There is a clear direction so going backwards brings you to the begin.
I'm English, not American but I see it as Saturday and Sunday are the two ends of the week. Like how a string has two ends. The weekend is both the start and the finishing end of the week.
- So, when someone asks if you are free the next two weekends, you assume they're talking about the next Saturday (tail weekend) and the next Sunday (front weekend)?
- since we are in a temporal context here i would argue that there is a clear distrinction between beginning and end here

weekend = day_of_week in (“sat”, “sun”)

As a bonus this completely sidesteps the issue of what day is 0 or 1.

Until some idiot sends in "Sunday" as days of the week...
- /^(sun|sat)/i.test(day_of_week)
  
  👍
yeah I like having an array of days that are weekend days then testing if the day is in the array. can change what days are considered weekend if we go to a three day weekend and it reads really well. I hate massive if statements

You forgot weekend = dayOfWeek.name[0] == 'S';

Can confirm this works completely as expected when the user's system is set to lang=ES.
- Simple save the users language setting in a variable, change it to english, check if the first letter is "s" and then change the language back.
- true but that's a precondition to some of the other examples as well

weekend = dayOfWeek > 5

dayOfWeek is clearly represented by 1-7 in the example, with Sunday being 1.

So, I guess the answer is “depends on what date library you’re linking against”
Sunday is 1 0 and Saturday is 7 6. ~~You just made Friday part of the weekend~~ You forgot Sunday
- On which planet? Monday is 1

Interesting that your days are 1-indexed. What happens on nullday?

I'd make it a named function for clarity and testability and proceed to give zero shits how it is implemented. I would unironically write this code if it worked, but I wouldn't inline it to reduce the cognitive load of reading it.

This, and maybe a couple of unit tests
- 7 unit tests should be enough I think

Image Transcription: Meme

[Paneled meme with a brain that gets increasingly glowing]

[The brain is smaller than the skull]

if dayOfWeek.name == "Sunday" || dayOfWeek.name == "Saturday"
    weekend = true

[The brain is glowing in some areas]

if dayOfWeek &lt; 2 || dayOfWeek > 6
    weekend = true

[The brain is shooting out rays of light]

weekend = !((dayOfWeek - 1) % 6)

I am a human volunteer who transcribes posts to improve accessibility on programming.dev and you could be one too! !transcribing@programming.dev

Depending on whether this code is in a hotpath (and considering how "elementary" it is, I figure that's a possibility), this could very well be a significant speed improvement.

Though I'd say that only excuses it if it's truly an elementary function (and not one line as part of a larger function), as otherwise it's unreadable garbage. But on its own it:

has a clear purpose
(presumably) isn't reimplementing functionality
is easily tested
can be modified with no side effects (besides breaking your calendar, but that's beside the point)

It's one line as part of a larger function. Also, it doesn't actually say weekend, it just executes some other functionality if !(day % 6). I made it more readable so that everyone here could understand what it does