4 ms·

You can do it in a consistent way, for example always store the timestamp at 00:00 UTC. But that's not obvious just by looking at the values, which is why it ca

You can do it in a consistent way, for example always store the timestamp at 00:00 UTC. But that's not obvious just by looking at the values, which is why it can be ambiguous. And when parsing those values, you could do for example (JS) `new Date(ts*1000).getDay()`. Of course that's not correct - you need to use the UTC methods. But it's easy to miss, and may pass all your tests until you switch the timezone. Those aren't massive issues - you just have to be careful with the parsing and serialization, and you need to be careful in any case. It just explains my personal preference.

vlovich123 3y ago
Not sure I follow. What's the difference between `new Date(ts).getDay()` when ts is an ISO8601 string or a ms since UNIX epoch value. Pretty sure the result is the same and whether you need to use `getDay` or `getUTCDay` is a display issue that affects both variants. I could see it being more convenient if you're just dumping the raw values without any transformation or you don't know what data type is stored in a column, but otherwise the difference seems largely one of taste and not so much relative error rates?
- joking 3y ago
  when you do that, it will give you different days depending on your timezone. 1701388800 is 2023-12-01 in london, but still 2023-11-30 on new york.
  - vlovich123 3y ago
    Sure, but that’s also true for an iso8601 string unless you’re extracting things directly. But also you’re assuming that your iso8601 string is in local time which it may not be (eg string generated in London but accessed in New York). Localizing things to be time zone aware in a way that meets user expectations is hard because it’s a squishy domain specific UX problem, not a technical one so arguing about it like a technical issue feels like a wrong approach.
- matharmin 3y ago
  You're right that you'll have exactly the same issues if you use Date with a string. However, with a string date you can bypass the Date class completely in many use cases. My experience with this is anecdotal, but I've ran into many bugs due to conversion between day-precision values and Date objects. One example was a date picker library that returned values at 00:00 in the local timezone instead of UTC, which were then not correctly converted to UTC-based values before being persisted. Once again, these are all preventable issues - just use UTC everywhere. I've just seen issues like that happen enough that I prefer never converting between dates and timestamps if I can avoid it.
  - zlg_codes 3y ago
    > My experience with this is anecdotal, but I've ran into many bugs due to conversion between day-precision values and Date objects. One example was a date picker library that returned values at 00:00 in the local timezone instead of UTC, which were then not correctly converted to UTC-based values before being persisted. Oh man, that sounds ugly, and an invitation for disaster. Lots of off-by-ones. In my project's case, I also need to do math with them for analytical purposes. It's a game collection manager, so it's tracking the day you bought, beat, and 100%d a game. I derive how long it took to beat a game by subtracting the UNIX timestamp of the purchase date from the beaten date's timestamp, then divide by (60*60*24) to measure days. It's handy to show games in the backlog and sort by purchase date, too, so you can target the games that've been sitting the longest. There are plans to graph out a collection in terms of its path from new to beaten to completed in a Gantt-style chart or something else fun. But yeah, I just thought to ask because in JSON I and others can read `2023-12-01`, but not `1701417600`. SQLite and Python can do conversions for the calculations, and Python even has the timedelta module that might make my comparisons easier to do or slightly more accurate. Edit: asterisks

vlovich123 3y ago

Not sure I follow. What's the difference between `new Date(ts).getDay()` when ts is an ISO8601 string or a ms since UNIX epoch value. Pretty sure the result is the same and whether you need to use `getDay` or `getUTCDay` is a display issue that affects both variants. I could see it being more convenient if you're just dumping the raw values without any transformation or you don't know what data type is stored in a column, but otherwise the difference seems largely one of taste and not so much relative error rates?

joking 3y ago
when you do that, it will give you different days depending on your timezone. 1701388800 is 2023-12-01 in london, but still 2023-11-30 on new york.
- vlovich123 3y ago
  Sure, but that’s also true for an iso8601 string unless you’re extracting things directly. But also you’re assuming that your iso8601 string is in local time which it may not be (eg string generated in London but accessed in New York). Localizing things to be time zone aware in a way that meets user expectations is hard because it’s a squishy domain specific UX problem, not a technical one so arguing about it like a technical issue feels like a wrong approach.
matharmin 3y ago
You're right that you'll have exactly the same issues if you use Date with a string. However, with a string date you can bypass the Date class completely in many use cases. My experience with this is anecdotal, but I've ran into many bugs due to conversion between day-precision values and Date objects. One example was a date picker library that returned values at 00:00 in the local timezone instead of UTC, which were then not correctly converted to UTC-based values before being persisted. Once again, these are all preventable issues - just use UTC everywhere. I've just seen issues like that happen enough that I prefer never converting between dates and timestamps if I can avoid it.
- zlg_codes 3y ago
  > My experience with this is anecdotal, but I've ran into many bugs due to conversion between day-precision values and Date objects. One example was a date picker library that returned values at 00:00 in the local timezone instead of UTC, which were then not correctly converted to UTC-based values before being persisted. Oh man, that sounds ugly, and an invitation for disaster. Lots of off-by-ones. In my project's case, I also need to do math with them for analytical purposes. It's a game collection manager, so it's tracking the day you bought, beat, and 100%d a game. I derive how long it took to beat a game by subtracting the UNIX timestamp of the purchase date from the beaten date's timestamp, then divide by (60*60*24) to measure days. It's handy to show games in the backlog and sort by purchase date, too, so you can target the games that've been sitting the longest. There are plans to graph out a collection in terms of its path from new to beaten to completed in a Gantt-style chart or something else fun. But yeah, I just thought to ask because in JSON I and others can read `2023-12-01`, but not `1701417600`. SQLite and Python can do conversions for the calculations, and Python even has the timedelta module that might make my comparisons easier to do or slightly more accurate. Edit: asterisks