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Comment by TekMol | Hacker News Reader

I never use any date library and I never had a problem with it.

I just use what the native Date() object offers.

Other devs always say "Just wait, one day it will fall on your feet".

But this has been going on for many years, in which my software has served millions of users and nothing ever fell on my feet. I think the complexity of a library like this (423 files, 1433 commits, 53004 lines of code) would have created more problems during this time. So not using one is a net positive.

Any minimal code example of what is prone to break without a date library and how this date library is supposed to prevent it?

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Examples of essential complexity you have to worry about if you want your code to be correct, and even if you want to test/detect all issues that can/do come up:

- https://infiniteundo.com/post/25326999628/falsehoods-program...

- https://infiniteundo.com/post/25509354022/more-falsehoods-pr...

In my experience engineers will often brush these sorts of things off as “edge cases”, but really all of these complexities are just how dates and time work in the real life (I’d argue that they’re just “normal cases” to test for)… So any anomaly in software will cause real problems of varying importance for users.

I only see this being an issue storing times as strings. Why not store them as integers (like a Unix timestamp) or at least some standardized string format? The only reasonable use case I can think of where you absolutely need all this complexity is if you're rendering a calendar or something similar.

There are countless, profitable business use cases for accurate time tracking.

    User: set an alarm in eight hours.

It's 10PM right now. At what time should the alarm be set? 6AM? Woops, tomorrow is the switch to DST! What now?

    User: remind me to brush my teeth on November 21st at 8AM.

Okay, will do! Wait, you took a plane on November 2nd and are now on the other side of the world? Should I remind you at 8AM or 5PM?

    User: please note my doctor's appointment in two weeks at 10AM.

Sure thing bub! Wait, but you live in Morocco in 2019? And the government just announced that reverse DST will be in effect for the month of Ramadan, which begins next week?! WTF do I do now?

---

tl;dr It's not just an issue of storage. Managing time is hard. There are requirements that we, as humans, will intuitively find the right interpretation for, that computers will absolutely break their teeth on.

> What now?

I mean, there is no way to write code to “handle” this that isn’t just guessing on the part of the programmer. The correct thing to do is to prompt the user for verification or further information.

> There are requirements that we, as humans, will intuitively find the right interpretation for…

Interpretation is subject to error. (Yes humans have immensely more context to work with than computer programs, but just because we we’re better guessers doesn’t mean we’re not still guessing.)

This was the reply I was trying to prevent by saying "minimal code example".

I'm not interested in long theoretical articles. But I would look at a few lines of code.

Here is an example of some code I recently wrote:

    logEvent {
        'date': new Date().toISOString(),
        'event': 'image_updated',
        'value': image['id'],
    }

This logs that an image with a given id was updated.

Why would I trade in my single date line for 423 files with 53004 lines of code?

You wouldn't. It's not a trade anyone is asking.

This is only you having super basic date needs, not Day.js being overkill in general.

Any system, no matter how complex, can be composed of smaller units that only have super basic needs.

*if all complexity has been hidden from the developer which only needs to use a decent puplic API.

I'd agree that it feels like that quiet often as a web developer, but that's only because most of our APIs are actually quiet easy to use.

The illusion usually falls away if you look at the code of that API, however.

> I'm not interested in long theoretical articles

Those articles are more empirical in nature than theoretical.

> This logs that an image with a given id was updated

As a thought exercise, imagine that your log trail needed to be created in a distributed system, spanning multiple machine time zones, or that you needed to build a report that is read from browsers in multiple time zones that differ from multiple differing written time zones, and you need to account for human readable things like knowing what day of the week it is and what some given locale calls that day.

If you are doing the equivalent of printf debugging with your times, maybe you likely don’t need a time library.

If you are using time as a central part of a distributed algorithm, web content, or a business workflow, then you may likely need a time library.

You are trying to convince me with the popular "This is not going to work for a much more complex system".

I heard it very often. I don't buy it. Any system, no matter how complex, can be composed of small, simple systems.

I never ran against a "complexity wall" when writing software in a lean way and suddenly thought "Damn, those tens of thousands of lines of library code now would be the better approach".

That’s very true. A colleague recently started using the same method and is achieving bundles and dependencies orders of magnitude smaller. As a result, he has to care less about security, build times and build breaks and spends more time coding. Developers have unlearned to build basic functionality apparently, especially in the front end area.

It’s not really a question of unlearning, its more of a question of economics.

Sound software construction techniques are one thing, but convincing someone to pay you to reinvent the wheel is another.

Especially when you consider that budgets for new, bespoke brand websites can start as low as about a couple of days pay for a senior developer.

More power to you if you have the budget to spend time writing code that someone else has already written.

I think you’re missing the point entirely. If Date has a method that does what you need, by all means use it directly.

Libraries come in handy when doing things that aren’t one liners.

A colleague thought it was super easy to change that exact ISO string to use the local timezone instead of UTC, against my advice. Guess what. The minus sign broke it and he would have never known because most customers are in the US, then they travel to Singapore and your product is worthless. By the time you hear about it, you lost the customer’s money and time therefore you lost the customer.

Moment and Luxon are too heavy, I agree, but date-fns isn’t.

Moment and friends shine when you need to display and interact with dates from a human perspective. Calendars, scheduled events, etc., all are hard to do without something like moment.

You can still add a library once it’s really needed and an area is proved to cause bugs. Most of the times though, developers will add them upfront “just in case”, making the bundles always heavier and thus harming the user experience with a slower UI.

I’d argue that we already know how time works, so the proof exists up front and there is no “just in case”.

You could make an argument that there are more important things to fix, but then you’d be deciding consciously that it was okay to ship software known to be incorrect.

I posted about this elsewhere in the comments, but my experience with day.js is that if you're concerned with these kinds of corner cases, maybe day.js isn't the library for you.[1][2]

[1]: https://github.com/iamkun/dayjs/issues/1816

[2]: https://github.com/iamkun/dayjs/issues/1817

Users in timezone A need to schedule events many months in the future in timezone B, and display them in a report in timezone C.

In addition, should the legal authority in timezone B change their DST rules in the meantime, the local time of the event as observed in timezone B should still be what the user initially selected, which is not the same in UTC as it was at creation time

Any operation like adding/substracting months from a date is very messy to implement yourself.

What is one month ago when you are March, 31st?

We have to deal with monthly subscriptions and it's not fun.

First you have to define what you mean by "one month ago". Is it 30 days ago? Or last month? Or a certain number of milliseconds ago?

No library can help you with that. You have to define what you actually want to calculate.

At some point you will need to calculate how many leap years to account for and whether or not a leap second was introduced in between two arbitrary times.

Time libraries can help you with that.

Exactly there is the same problem, to a lesser extend, when adding/subtracting years which is not trivial to do properly.

Let alone determining requirements for thresholds.

This discussion reminds me of this bug report: https://bugzilla.mozilla.org/show_bug.cgi?id=1715455

Why can’t you use Date.getFullYear with setFullYear?

Absolutely. moment has a definition of that and compute it in a consistent way, which is useful. But if you want to come up with a different definition then it cannot help you indeed.

>What is one month ago when you are March, 31st?

"one month ago" is between "a few weeks ago" and "a few months ago".

>We have to deal with monthly subscriptions and it's not fun.

it is a lot less unfun if you define a month as N calendar days in your terms of service, like virtually everyone does

Yes, that's what we do mostly, except to track external subscriptions that actually use months (I believe the Google playstore does that but I could be mistaken with another service)

And they would be guilty of misleading the consumer when doing so, and possibly accounting fraud as well because neither GAAP nor IFRS recognise such a calendar; the closest available is the 4-4-5 standard.

This is why we don’t let engineers write contracts. Many seem to think that law is a programming language in which they can redefine reality. It ain’t.

Can you write a one liner to give me the timestamp for start or end of current week, or month? How about a text representation of a difference between two dates? Relative date string (eg. “2 weeks ago”)? Date comparison between two dates that are in different time zones? Does your date calculations take leap hours and leap seconds into account? Date libraries make all these and many more operations a breeze, while rolling these on your own can be tricky, error prone and you’ll be just wasting your time.

> Can you write a one liner to give me the timestamp for start or end of current week, or month?

And... it's a multi tenant system, where some organizations use Sunday as the start of a week, and some use Monday. And they all want to be able to switch.

I've always found moment to just present the same problems you would otherwise have with a few new ones tacked on stated in a different and more complicated way but with a pitch site and artwork.

The js date is a bit primitive and moment looks easier but in practice it's actually a convoluted clunky type system that hides important nuance behind impressively bad defaults.

I approach all of these "better than what the language offers" solutions the same way: it would be truly remarkable if some kid had a more nuanced and correct take then people with years of experience and PhDs in language design who made the language but more likely, I think the kid who wrote the library is just better at drawing cartoon characters, hype posting on social media and making something popular.

I used to get immediate hostility and belittling insults when I stated this about 10 years ago. I think people have finally come around. Let's see how the replies go.

Who is "some kid"?

Intentionally unspecified. This isn't a personal attack but instead a systemic and cultural critique

It's been like this for decades. Emotional salience sells software better than hard practicality to just about everyone. Then people rationalize their irrational choices then the timeline slips and the product sucks.

You can just sit and watch it play out like someone studying monkeys. It's remarkably predicable.

As important as the relatively low file size is for the utility of this library, the API compatibility with Moment is perhaps the magnum opus.

Absolutely. Great job. No question. Everyone should build things and follow their heart. Full stop.

This wasn't anything about the posted software. It was a reply to a comment.

For sure.

Formal peer-review does trump download count, nonetheless.

And I’m all for professional licensure, continuing education programs, and formal, public reviews of the software engineering behind the open source libraries that comprise global infrastructure.

Your main point wasn’t missed.

How accurate can your critique be if you're so inaccurate in your metaphor for the library authors?

I'm not a primatologist.

Tell me if you've ever had this experience.

You see something that looks like it's pretty popular. You try it. You find it has nothing but problems. After much research you then find out that other people don't have the level of sophisticated asks for the product and they are doing less complicated and less critical things.

It's the disconnect between the hype and the reality that really rubs me the wrong way. I've personally lost so much time on inappropriate tools.

Again I'm not here to insult anybody specifically or to speak poorly upon any specific product. I know how many people read these comments and I don't want to cast shade on anybody's hard work. I just wish there was more authenticity to the fit and purpose of things.

I know a lot of this depends on the users. I speak as somebody who has very popular projects and very not so popular projects. The popular ones are hyped (but sarcastically) and the ones that I worked very hard on to be extremely technical about do quite poorly.

To make things super current I haven't working for about a month on an article and I have been making sure it is extremely accurate and I know that that will probably hurt me because the liberties which inherently contain inaccuracy are simply more entertaining

This is a shared experience except for a select few. This carries is over to other things. Inaccurate pop science is read much more widely then the direct research material. There's something more emotionally approachable through this tactic. It just hurts productivity and it's a shame

> I think the kid who wrote the library is just better at drawing cartoon characters

Quoting your writing that is probably rubbing others the wrong way, as it certainly reads easily as being specific to “these” solutions, as you put it.

You might avoid triggering people’s negative emotions by sticking to your main point and avoiding the marginalizing.

> I just wish there was more authenticity to the fit and purpose of things.

This is so vague. Can you say how you're relating this to dayjs? How is its purpose inauthentic?

Must be a euphemism for “300 contributors on a js.org supported GitHub project”.

Immediate hostility and belittling attacks strike again.

That was a reply to a comment, not to the code posted. You're being sloppy imprecise and presumptive and expressing it as haughty snide arrogance.

Cool attitude

You are succumbing to the fundamental attribution error.

You described your comment being an attack on modern development culture, as your use of euphemism, you chose the insultingly denotative word “kid” to attack the project.

Cool attitude, too?

No I was not.

You're being sloppy imprecise and presumptive once again. I'm noticing a pattern here. Let's see if it comes in threes.

And in case you're wondering, you're the one who set the rules of this engagement, I'm only playing by them.

We can be adults any time you want.

> Immediate hostility and belittling attacks strike again.

Nothing about that comment was belittling or hostile. It was a bit snarky, but with very good reason, and did not name its target.

Hopefully the replies are the same - this is a dismissive and ill-informed view that you’ve taken as a result of your own ignorance and gatekeeping.

different countries use different date format and also how do you manage languages?

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