index.js

var MILLISECONDS_IN_HOUR = 3600000
var MILLISECONDS_IN_MINUTE = 60000
var DEFAULT_ADDITIONAL_DIGITS = 2

var patterns = {
  dateTimeDelimeter: /[T ]/,
  plainTime: /:/,

  // year tokens
  YY: /^(\d{2})$/,
  YYY: [
    /^([+-]\d{2})$/, // 0 additional digits
    /^([+-]\d{3})$/, // 1 additional digit
    /^([+-]\d{4})$/ // 2 additional digits
  ],
  YYYY: /^(\d{4})/,
  YYYYY: [
    /^([+-]\d{4})/, // 0 additional digits
    /^([+-]\d{5})/, // 1 additional digit
    /^([+-]\d{6})/ // 2 additional digits
  ],

  // date tokens
  MM: /^-(\d{2})$/,
  DDD: /^-?(\d{3})$/,
  MMDD: /^-?(\d{2})-?(\d{2})$/,
  Www: /^-?W(\d{2})$/,
  WwwD: /^-?W(\d{2})-?(\d{1})$/,

  HH: /^(\d{2}([.,]\d*)?)$/,
  HHMM: /^(\d{2}):?(\d{2}([.,]\d*)?)$/,
  HHMMSS: /^(\d{2}):?(\d{2}):?(\d{2}([.,]\d*)?)$/,

  // timezone tokens
  timezone: /([Z+-].*)$/,
  timezoneZ: /^(Z)$/,
  timezoneHH: /^([+-])(\d{2})$/,
  timezoneHHMM: /^([+-])(\d{2}):?(\d{2})$/
}

/**
 * @name toDate
 * @category Common Helpers
 * @summary Convert the given argument to an instance of Date.
 *
 * @description
 * Convert the given argument to an instance of Date.
 *
 * If the argument is an instance of Date, the function returns its clone.
 *
 * If the argument is a number, it is treated as a timestamp.
 *
 * If an argument is a string, the function tries to parse it.
 * Function accepts complete ISO 8601 formats as well as partial implementations.
 * ISO 8601: http://en.wikipedia.org/wiki/ISO_8601
 *
 * If the argument is null, it is treated as an invalid date.
 *
 * If all above fails, the function passes the given argument to Date constructor.
 *
 * **Note**: *all* Date arguments passed to any *date-fns* function is processed by `toDate`.
 * All *date-fns* functions will throw `RangeError` if `options.additionalDigits` is not 0, 1, 2 or undefined.
 *
 * @param {*} argument - the value to convert
 * @param {Options} [options] - the object with options. See [Options]{@link https://date-fns.org/docs/Options}
 * @param {0|1|2} [options.additionalDigits=2] - the additional number of digits in the extended year format
 * @returns {Date} the parsed date in the local time zone
 * @throws {TypeError} 1 argument required
 * @throws {RangeError} `options.additionalDigits` must be 0, 1 or 2
 *
 * @example
 * // Convert string '2014-02-11T11:30:30' to date:
 * var result = toDate('2014-02-11T11:30:30')
 * //=> Tue Feb 11 2014 11:30:30
 *
 * @example
 * // Convert string '+02014101' to date,
 * // if the additional number of digits in the extended year format is 1:
 * var result = toDate('+02014101', {additionalDigits: 1})
 * //=> Fri Apr 11 2014 00:00:00
 */
export default function toDate (argument, dirtyOptions) {
  if (arguments.length < 1) {
    throw new TypeError('1 argument required, but only ' + arguments.length + ' present')
  }

  if (argument === null) {
    return new Date(NaN)
  }

  var options = dirtyOptions || {}

  var additionalDigits = options.additionalDigits === undefined ? DEFAULT_ADDITIONAL_DIGITS : Number(options.additionalDigits)
  if (additionalDigits !== 2 && additionalDigits !== 1 && additionalDigits !== 0) {
    throw new RangeError('additionalDigits must be 0, 1 or 2')
  }

  // Clone the date
  if (argument instanceof Date) {
    // Prevent the date to lose the milliseconds when passed to new Date() in IE10
    return new Date(argument.getTime())
  } else if (typeof argument !== 'string') {
    return new Date(argument)
  }

  var dateStrings = splitDateString(argument)

  var parseYearResult = parseYear(dateStrings.date, additionalDigits)
  var year = parseYearResult.year
  var restDateString = parseYearResult.restDateString

  var date = parseDate(restDateString, year)

  if (date) {
    var timestamp = date.getTime()
    var time = 0
    var offset

    if (dateStrings.time) {
      time = parseTime(dateStrings.time)
    }

    if (dateStrings.timezone) {
      offset = parseTimezone(dateStrings.timezone)
    } else {
      // get offset accurate to hour in timezones that change offset
      offset = new Date(timestamp + time).getTimezoneOffset()
      offset = new Date(timestamp + time + offset * MILLISECONDS_IN_MINUTE).getTimezoneOffset()
    }

    return new Date(timestamp + time + offset * MILLISECONDS_IN_MINUTE)
  } else {
    return new Date(argument)
  }
}

function splitDateString (dateString) {
  var dateStrings = {}
  var array = dateString.split(patterns.dateTimeDelimeter)
  var timeString

  if (patterns.plainTime.test(array[0])) {
    dateStrings.date = null
    timeString = array[0]
  } else {
    dateStrings.date = array[0]
    timeString = array[1]
  }

  if (timeString) {
    var token = patterns.timezone.exec(timeString)
    if (token) {
      dateStrings.time = timeString.replace(token[1], '')
      dateStrings.timezone = token[1]
    } else {
      dateStrings.time = timeString
    }
  }

  return dateStrings
}

function parseYear (dateString, additionalDigits) {
  var patternYYY = patterns.YYY[additionalDigits]
  var patternYYYYY = patterns.YYYYY[additionalDigits]

  var token

  // YYYY or ±YYYYY
  token = patterns.YYYY.exec(dateString) || patternYYYYY.exec(dateString)
  if (token) {
    var yearString = token[1]
    return {
      year: parseInt(yearString, 10),
      restDateString: dateString.slice(yearString.length)
    }
  }

  // YY or ±YYY
  token = patterns.YY.exec(dateString) || patternYYY.exec(dateString)
  if (token) {
    var centuryString = token[1]
    return {
      year: parseInt(centuryString, 10) * 100,
      restDateString: dateString.slice(centuryString.length)
    }
  }

  // Invalid ISO-formatted year
  return {
    year: null
  }
}

function parseDate (dateString, year) {
  // Invalid ISO-formatted year
  if (year === null) {
    return null
  }

  var token
  var date
  var month
  var week

  // YYYY
  if (dateString.length === 0) {
    date = new Date(0)
    date.setUTCFullYear(year)
    return date
  }

  // YYYY-MM
  token = patterns.MM.exec(dateString)
  if (token) {
    date = new Date(0)
    month = parseInt(token[1], 10) - 1
    date.setUTCFullYear(year, month)
    return date
  }

  // YYYY-DDD or YYYYDDD
  token = patterns.DDD.exec(dateString)
  if (token) {
    date = new Date(0)
    var dayOfYear = parseInt(token[1], 10)
    date.setUTCFullYear(year, 0, dayOfYear)
    return date
  }

  // YYYY-MM-DD or YYYYMMDD
  token = patterns.MMDD.exec(dateString)
  if (token) {
    date = new Date(0)
    month = parseInt(token[1], 10) - 1
    var day = parseInt(token[2], 10)
    date.setUTCFullYear(year, month, day)
    return date
  }

  // YYYY-Www or YYYYWww
  token = patterns.Www.exec(dateString)
  if (token) {
    week = parseInt(token[1], 10) - 1
    return dayOfISOYear(year, week)
  }

  // YYYY-Www-D or YYYYWwwD
  token = patterns.WwwD.exec(dateString)
  if (token) {
    week = parseInt(token[1], 10) - 1
    var dayOfWeek = parseInt(token[2], 10) - 1
    return dayOfISOYear(year, week, dayOfWeek)
  }

  // Invalid ISO-formatted date
  return null
}

function parseTime (timeString) {
  var token
  var hours
  var minutes

  // hh
  token = patterns.HH.exec(timeString)
  if (token) {
    hours = parseFloat(token[1].replace(',', '.'))
    return (hours % 24) * MILLISECONDS_IN_HOUR
  }

  // hh:mm or hhmm
  token = patterns.HHMM.exec(timeString)
  if (token) {
    hours = parseInt(token[1], 10)
    minutes = parseFloat(token[2].replace(',', '.'))
    return (hours % 24) * MILLISECONDS_IN_HOUR +
      minutes * MILLISECONDS_IN_MINUTE
  }

  // hh:mm:ss or hhmmss
  token = patterns.HHMMSS.exec(timeString)
  if (token) {
    hours = parseInt(token[1], 10)
    minutes = parseInt(token[2], 10)
    var seconds = parseFloat(token[3].replace(',', '.'))
    return (hours % 24) * MILLISECONDS_IN_HOUR +
      minutes * MILLISECONDS_IN_MINUTE +
      seconds * 1000
  }

  // Invalid ISO-formatted time
  return null
}

function parseTimezone (timezoneString) {
  var token
  var absoluteOffset

  // Z
  token = patterns.timezoneZ.exec(timezoneString)
  if (token) {
    return 0
  }

  // ±hh
  token = patterns.timezoneHH.exec(timezoneString)
  if (token) {
    absoluteOffset = parseInt(token[2], 10) * 60
    return (token[1] === '+') ? -absoluteOffset : absoluteOffset
  }

  // ±hh:mm or ±hhmm
  token = patterns.timezoneHHMM.exec(timezoneString)
  if (token) {
    absoluteOffset = parseInt(token[2], 10) * 60 + parseInt(token[3], 10)
    return (token[1] === '+') ? -absoluteOffset : absoluteOffset
  }

  return 0
}

function dayOfISOYear (isoYear, week, day) {
  week = week || 0
  day = day || 0
  var date = new Date(0)
  date.setUTCFullYear(isoYear, 0, 4)
  var fourthOfJanuaryDay = date.getUTCDay() || 7
  var diff = week * 7 + day + 1 - fourthOfJanuaryDay
  date.setUTCDate(date.getUTCDate() + diff)
  return date
}