DateInfo

• Node module that helps with the Gregorian calendar.
• Especially good for week numbering.
• No bloated feature set: six methods, four classes.

Installation

npm install date-info

Example Usage

1. Iterate over all weeks

const DateInfo = require('date-info')

DateInfo.year(2017).weeks.forEach(week => {
  const begin = week.days.get(0)
  const end   = week.days.get(week.days.length - 1)

  const from  = `${begin.date}/${begin.month}`
  const to    = `${end.date}/${end.month}`

  console.log(`Week ${week.week}: ${from} to ${to}`)
})

Output:

Week 52: 1/1 to 1/1
Week 1:  2/1 to 8/1
Week 2:  9/1 to 15/1
Week 3: 16/1 to 22/1
...
Week 50: 11/12 to 17/12
Week 51: 18/12 to 24/12
Week 52: 25/12 to 31/12

2. Iterate over all weeks in every month

DateInfo.year(2017).months.forEach(month => {

  console.log(`===== Month ${month.month} =====`)

  month.weeks.forEach(week => {
    const begin = week.days.get(0)
    const end   = week.days.get(week.days.length - 1)

    const from  = `${begin.date}/${begin.month}`
    const to    = `${end.date}/${end.month}`

    console.log(`Week ${week.week}: ${from} to ${to}`)
  })

})

Output:

===== Month 1 =====
Week 52: 1/1 to 1/1
Week 1: 2/1 to 8/1
Week 2: 9/1 to 15/1
Week 3: 16/1 to 22/1
Week 4: 23/1 to 29/1
Week 5: 30/1 to 31/1  <-- Notice how Week 5 is cut in half. One
===== Month 2 =====       part is in January, the other part is
Week 5: 1/2 to 5/2        in February.
Week 6: 6/2 to 12/2
Week 7: 13/2 to 19/2
Week 8: 20/2 to 26/2
Week 9: 27/2 to 28/2
===== Month 3 =====
Week 9: 1/3 to 5/3
Week 10: 6/3 to 12/3
Week 11: 13/3 to 19/3
Week 12: 20/3 to 26/3
Week 13: 27/3 to 31/3
...

3. Specific date information

const info = DateInfo.date(2017, 8, 31)

console.log(`Year:  ${info.year}`)               // Year:  2017
console.log(`Month: ${info.month}`)              // Month: 8
console.log(`Date:  ${info.date}`)               // Date:  31

console.log(`Day:   ${info.day}rd day of 2017`)  // Day:   243rd day of 2017
console.log(`Week:  ${info.week}`)               // Week:  35
console.log(`Day of week: ${info.weekDay}`)      // Day of week: 4 (Thursday)

4. Jump forwards and backwards in time

function print(msg, { year, month, date }) {
  console.log(`${msg} ${year}/${month}/${date}`)
}

const x = DateInfo.date(2017, 1, 5)
print('Original: ', x)                  // Original:  2017/1/5
print('+4 days:  ', x.jumpDays(4))      // +4 days:   2017/1/9
print('-8 days:  ', x.jumpDays(-8))     // -8 days:   2016/12/28
print('+1 week:  ', x.jumpWeeks(2))     // +1 week:   2017/1/19
print('+2 months:', x.jumpMonths(2))    // +2 months: 2017/3/5
print('-4 months:', x.jumpMonths(-4))   // -4 months: 2016/9/5
print('+2 years: ', x.jumpYears(2))     // +2 years:  2019/1/5

Documentation: Methods

DateInfo.year(year)

Takes one integer as the full year, returns a year object. Example usage:

const yr2017 = DateInfo.year(2017)

DateInfo.month(year, month)

Takes integer arguments, returns a month object. Months are counted from 1 (i.e. 1 = January, 12 = December). Alternatively you can use the built in constants DateInfo.JAN, DateInfo.FEB, etc...

Example usage:

const august = DateInfo.month(2017, DateInfo.AUG)

DateInfo.week(year, weekNumber)

Takes integer arguments, returns a week object. Standard week numbers are used.

Example usage:

const week31 = DateInfo.week(2017, 31)

The week returned will only include days that are in the year you want. If a week starts in your year but extends into the next, the days which are in the next year won't be included in the returned week object. Instead they will be in DateInfo.year(year+1).weeks.get(0)

DateInfo.week(year, month, weekNumber) (alternative usage)

Takes integer arguments, returns a week object. By giving a month, the days included in the week will only be those that are in the given month.

Example usage:

// Normal:
const week31 = DateInfo.week(2017, 31)

// Week 31 starts in July and ends in August.
// If you only want the part of week 31 that
// is in August, do this:
const w31aug = DateInfo.week(2017, 8, 31)

// As a result:
console.log(week31.days.length)  // 7
console.log(w31aug.days.length)  // 6

DateInfo.date(year, month, date)

Takes integer arguments, returns a day object. Example usage:

const may1st = DateInfo.date(2017, 5, 1)

DateInfo.day(year, day)

Takes integer arguments, returns a day object. Example usage:

const day200 = DateInfo.day(2017, 200)  // 200th day of 2017

DateInfo.weekDay(year, weekNumber, weekDay)

Takes integer arguments, returns a day object. Week days are counted from 1 (i.e. 1 = Monday, 7 = Sunday). Alternatively you can use the built in constants DateInfo.MON, DateInfo.TUE, etc...

Example usage:

const wk6tue = DateInfo.weekDay(2017, 6, 2) // Tuesday, week 6

DateInfo.fromId(id)

Takes an integer id, returns a day object. Every day is uniquely identified with an id. The id represents the number of days since 1970-01-01. You can use fromId() to turn an id into a day object.

Example usage:

const may1st = DateInfo.date(2017, 5, 1)
const may2nd = DateInfo.fromId(may1st.id + 1)

Documentation: Classes

The year object

yr2017 = {
  year: 2017,
  isLeapYear: false,
  months: VirtualizedArray,
  weeks: VirtualizedArray,
  days: VirtualizedArray
}

All arrays are in the form of VirtualizedArrays. None of their elements are calculated unless you need them. See below how VirtualizedArray works.

The month object

august = {
  year: 2017,
  month: 8,
  weeks: VirtualizedArray,
  days: VirtualizedArray
}

The week object

week31 = {
  year: 2017,
  month: 7,   // Month of the first day
  week: 31,
  days: VirtualizedArray
}

The day object

may1st = {
  id:      17287,  // 1970/1/1 + 17287 = 2017/5/1
  year:    2017,
  day:     121,    // 121st day of 2017
  month:   5,
  date:    1,
  weekDay: 1,      // Monday
  week:    18,

  jumpDays:   n => ...,
  jumpWeeks:  n => ...,
  jumpMonths: n => ...,
  jumpYears:  n => ...
}

jumpDays(2) returns May 3rd, jumpWeeks(1) returns May 8th, jumpMonths(-2) returns March 1st, jumpYears(1) return May 1st 2018.

The VirtualizedArray object

Let's assume virtual is a virtualized version of the array: actual. In that case:

virtual.length      === actual.length
virtual.get(i)      === actual[i]
virtual.map(fn)     === actual.map(fn)
virtual.forEach(fn) === actual.forEach(fn)
virtual.filter(fn)  === actual.filter(fn)
virtual.toArray()   === actual

Appendix: month numbering, week day numbering

Months are counted from 1 = January to 12 = December. Week days are counted from 1 = Monday to 7 = Sunday. You can also use the constants included in the package:

DateInfo.MON === 1
DateInfo.TUE === 2
DateInfo.WED === 3
DateInfo.THU === 4
DateInfo.FRI === 5
DateInfo.SAT === 6
DateInfo.SUN === 7

DateInfo.JAN === 1
DateInfo.FEB === 2
DateInfo.MAR === 3
DateInfo.APR === 4
DateInfo.MAY === 5
DateInfo.JUN === 6
DateInfo.JUL === 7
DateInfo.AUG === 8
DateInfo.SEP === 9
DateInfo.OCT === 10
DateInfo.NOV === 11
DateInfo.DEC === 12