time-values/index.js

Gets date/time attributes from a date or string with no dependencies

const emptyObj = { year: 0, month: 0, day: 0, hour: 0, minute: 0, second: 0 }

const stringNums = (start = 0, end = 0) => Array.from(Array(end - start + 1), (_, i) => `${i + start}`)

const getTimeValues = (inputDate = new Date()) => {
  if (!inputDate) {
    return { ...emptyObj }
  }

  // Assume this is a time-values output object, and fill in the blanks
  if (!(inputDate instanceof Date) && inputDate instanceof Object) {
    let year = inputDate.year == null ? new Date().getFullYear() : +inputDate.year
    let month = inputDate.month == null ? new Date().getMonth() + 1 : +inputDate.month
    let day = inputDate.day == null ? new Date().getDate() : +inputDate.day
    let hour = inputDate.hour == null ? new Date().getHours() : +inputDate.hour
    let minute = inputDate.minute == null ? new Date().getMinutes() : +inputDate.minute
    let second = inputDate.second == null ? new Date().getSeconds() : +inputDate.second

    // Loop around values out of range
    while (second >= 60) { second -= 60; minute++ }
    while (second < 0) { second += 60; minute-- }

    while (minute >= 60) { minute -= 60; hour++ }
    while (minute < 0) { minute += 60; hour-- }

    while (hour >= 24) { hour -= 24; day++ }
    while (hour < 0) { hour += 24; day-- }

    while (month > 12) { month -= 12; year++ }
    while (month < 1) { month += 12; year-- }

    // days are trickier because they're based off the days in a given month

    while (day > new Date(year, month, 0).getDate()) {
      day -= new Date(year, month, 0).getDate()
      month++
      while (month > 12) { month -= 12; year++ }
    }

    while (day < 1) {
      month--
      while (month < 1) { month += 12; year-- }
      day += new Date(year, month, 0).getDate()
    }

    return { year, month, day, hour, minute, second }
  }

  // String dates often have weird, special handling
  if (typeof inputDate === 'string') {
    // mm/dd/yyyy dates are a little wonky because they are always considered local tz, not UTC.
    if (/^\d{2}\/\d{2}\/\d{4}$/.test(inputDate)) {
      const [month, day, year] = inputDate.split('/')
      return { ...emptyObj, year: +year, month: +month, day: +day }
    }

    // ISO dates that don't specify a time should default to the start of the day
    // (amusingly this only applies for properly formatted ISO dates, so 2022-2-2 is fine)
    if (/^\d{4}\-\d{2}\-\d{2}$/.test(inputDate)) {
      const [year, month, day] = inputDate.split('-')
      return { ...emptyObj, year: +year, month: +month, day: +day }
    }

    // A year followed by a time value (separated by a 'T')
    if (/^\d{4}T/.test(inputDate)) {
      const [year, timeRaw] = inputDate.split('T')
      const [hour, minute, second] = timeRaw.split('.')[0].split(':').map(n => +n)
      return { year: +year, month: 1, day: 1, hour, minute, second }
    }

    // A year followed by a time value (separated by a ':')
    if (/^\d{4}:/.test(inputDate)) {
      const year = inputDate.substring(0, inputDate.indexOf(':'))
      const timeRaw = inputDate.substring(inputDate.indexOf(':') + 1)
      const [hour, minute, second] = timeRaw.split('.')[0].split(':').map(n => +n)
      return { year: +year, month: 1, day: 1, hour, minute, second }
    }

    // yyyy-mm with no day format defaults to the first of the month at hour 0
    if (/^\d{4}-\d{2}$/.test(inputDate)) {
      const year = inputDate.substring(0, inputDate.indexOf('-'))
      const month = inputDate.substring(inputDate.indexOf('-') + 1)
      return { year: +year, month: +month, day: 1, hour: 0, minute: 0, second: 0 }
    }

    // When just 1-4 digits are specified
    if (/^\d?\d?\d?\d$/.test(inputDate)) {
      // Yeah, this is a thing
      if (inputDate === '0') {
        return { ...emptyObj, year: 2000, month: 1, day: 1 }
      }

      // As is this
      if (stringNums(1, 12).includes(inputDate) || stringNums(1, 12).map(s => `0${s}`).includes(inputDate)) {
        return { ...emptyObj, year: 2001, month: +inputDate, day: 1 }
      }

      // Anything else that is just up to 4 digits is a year
      return { ...emptyObj, year: +inputDate, month: 1, day: 1}
    }
  }

  const date = new Date(new Date(inputDate).getTime() - new Date(inputDate).getTimezoneOffset() * 6e4)

  const [dateRaw, timeRaw] = date.toISOString().split('T')
  const [year, month, day] = dateRaw.split('-').map(v => parseInt(v, 10))
  const [hour, minute, second] = timeRaw.split('.')[0].split(':').map(n => +n)
  return { year, month: month, day, hour, minute, second }
}

getTimeValues.toDate = (timeValues) => {
  const p = s => `${s}`.padStart(2, '0')
  const t = getTimeValues(timeValues)
  return new Date(`${t.year}-${p(t.month)}-${p(t.day)}T${p(t.hour)}:${p(t.minute)}:${p(t.second)}`)
}

module.exports = getTimeValues