Return year and week

[Robin Millette]

Looking at the readme, this example cought my attention:

weekNumberSun(new Date(2016, 0, 2, 12)) // Sat
//> 52
weekNumberSun(new Date(2016, 0, 3, 12)) // Sun
//> 1

In the first case, it's actually week 52 of the year 2015. Would you like a patch to return the year along with the week? And while we're here, maybe even return the day (monday=1)

Looking at the ISO 8601 page it lists these examples:

• Monday 29 December 2008 is written "2009-W01-1"
• Sunday 3 January 2010 is written "2009-W53-7"

Maybe another method to return this format? Thoughts?

[commenthol]

This snippet returns what is in the README. So no need for a patch.

const {weekNumberSun} = require('weeknumber')
console.log(weekNumberSun(new Date(2016, 0, 2, 12)))
//> 52

With regards to the enhancement proposed. This lib just tries to provide low level functions. Feel free to create a lib which returns the Date in the ISO8601 week format.

[Robin Millette]

I didn't mean the example was wrong, but it's counterintuitive with week 52 coming before week 1 in early 2016. It's how the ISO weeks work, not arguing that.

My use case: group items by year-week in the correct order. I discovered I had a bug since I was using the year (as given to weekNumber and variants) followed by the week - but that assumption is wrong.

In other words, I'm wondering how useful it is to get the week number without its year.

I don't mind writing another package, but I though it would help complete yours. It's fine if you feel otherwise, you can close the issue.

P.S.: I didn't mean to use weekNumberSun when I opened the ticket, but the same applies to any variant.

[commenthol]

Finally I got your point. I am used to use-cases where only the calendar-week is required. E.g. like the unix command-line tool ncal -w 2010.
So for 2008-12-29 its calendar-week 1, albeit calendar-week-year is already 2009.

We could add some functions like that.

const getYear = (date, weekNo) => {
  let year = date.getFullYear()
  if (date.getMonth() === 11 && week === 1) year++
  if (date.getMonth() === 0 && week > 51) year--
  return year
}
const weeknumberYear = date => {
  const week = weekNumber(date)
  const year = getYear(date, week)
  const day = date.getDay() || 7
  return {year, week, day}
}
const weeknumberYearSun = date => {
  const week = weekNumberSun(date)
  const year = getYear(date, week)
  const day = (date.getDay() + 1) % 7 || 7
  return {year, week, day}
}
const weeknumberYearSat = date => {
  const week = weekNumberSat(date)
  const year = getYear(date, week)
  const day = (date.getDay() + 2) % 7 || 7
  return {year, week, day}
}

What do you think?

[Robin Millette]

Yeah :-)

Although day should probably start at 1 to be consistent with ISO 8601?

[commenthol]

day is in range 1...7.

[Robin Millette]

Doh! Trouble waking up....

Adding this feature would make my day :-)

[commenthol]

v1.1.0 should make you happy...