time.toSecondOfDay()

[thojanssens]

Can we provide a function to convert a Time to the total number of seconds of the day?

Similar to what Java and js-joda provide:
https://docs.oracle.com/javase/8/docs/api/java/time/LocalTime.html#toSecondOfDay--

[ptomato]

Filed under "feedback", thanks again! Here the same question, can you say anything more about the use case where you missed this method?

[justingrant]

Welcome, @thojanssens! Thanks so much for taking the time to review Temporal and give feedback. It's very helpful.

ECMAScript built-in objects tend to have fewer methods than OSS libraries built on top of those built-ins. The general philosophy is to expose few methods that can flexibly be applied to many different use cases. Therefore it's unlikely that Temporal would build a dedicated method for a use case like "how many seconds have elapsed so far today?".

However, the more general use case of "[unit] of [larger unit]" is an interesting one. There are already dayOfWeek, dayOfYear, weekOfYear properties on Date, DateTime, and (if #700 is accepted) LocalDateTime but I wonder if there is a more generalized "X of Y" solution possible... and if possible would it be needed?

For the specific case of "second of day", here's one way to do it.

function toSecondOfDay(timeLike) {
  const time = Temporal.Time.from(timeLike);
  const midnight = Temporal.Time.from('00:00');
  const diff = time.difference(midnight, {largestUnit: 'seconds'});
  return diff.seconds;
}
toSecondOfDay({hour: 12})
// => 43200
toSecondOfDay(Temporal.DateTime.from('2020-07-07T10:34:56'))
// => 38096
toSecondOfDay(Temporal.Time.from('12:00'))
// => 43200 (although currently 0. See note below.)

BTW, while writing this sample I found bug #735 in Temporal.Time.from which will make the third call above return 0 until #736 is merged.

[thojanssens]

@ptomato For example, get the difference between two times in total of seconds. AFAIK Duration doesn't give a value like "total of X".

@justingrant or

function toSecondOfDay(timeLike) {
  const time = Temporal.Time.from(timeLike);
  return time.hour * 60 * 60 + time.minute * 60 + time.second;
}

[ptomato]

To get the difference between two times in total of seconds, you can do time1.difference(time2, { largestUnit: 'seconds' }), and we are also intending to provide some way to round Temporal.Durations to the nearest unit (#337). (Not implying that this method shouldn't also be considered, but I'm mentioning them as alternatives.)

[justingrant]

AFAIK Duration doesn't give a value like "total of X".

Getting totals from an existing duration is discussed here: #584

[justingrant]

This use case has gotten a little easier from recent changes. Here's what this code will look like in a few days after #1064 lands:

[ptomato]

I believe these use cases are covered well enough now.

// toSecondOfDay as Justin mentioned above:
plainTime.since('00:00').total({ unit: 'seconds' })
// get the difference between two times in seconds:
time1.until(time2).total({ unit: 'seconds' })

I'm not sure there's anything to propose at https://github.com/js-temporal/proposal-temporal-v2/issues at this point, but please do if you think there is.