Duration#toISO() may not conform to ISO 8601.

Weeks should be expressed as days, isn’t it?

cf. https://en.wikipedia.org/wiki/ISO_8601#Durations

Example

const duration = Duration.fromObject({
  years: 3,
  months: 6,
  weeks: 1,
  days: 4,
  hours: 12,
  minutes: 30,
  seconds: 5
})
console.log(duration.toISO())

• expected: P3Y6M11DT12H30M5S
  • 1[weeks] + 4[days] = 7[days] + 4[days] = 11[days] -> 11D
• actual: P3Y6M1W4DT12H30M5S
  • 1W4D

FYI

Description of Java’s Period#parse():

ISO-8601 does not permit mixing between the PnYnMnD and PnW formats. Any week-based input is multiplied by 7 and treated as a number of days.

https://docs.oracle.com/en/java/javase/12/docs/api/java.base/java/time/Period.html#parse(java.lang.CharSequence)

[munierujp]

It seems that we need to buy to see it… 💸

https://www.iso.org/standard/70908.html

[icambron]

I think it’s a little awkward that we only get the W representation if the duration data is just so. Will only serve to surprise people that the strings look really different in some situations. So let’s have separate methods:

• toISO always converts weeks to days
• toISOWeeks converts the duration to weeks via as('weeks') and then just formats in that number of weeks