Go's time.ParseInLocation in TypeScript

How to use

Install via yarn add locutus and import: import { ParseInLocation } from 'locutus/golang/time/ParseInLocation'.

Or with CommonJS: const { ParseInLocation } = require('locutus/golang/time/ParseInLocation')

Use a bundler that supports tree-shaking so you only ship the functions you actually use. Vite, webpack, Rollup, and Parcel all handle this. For server-side use this is less of a concern.

Examples

These examples are extracted from test cases that automatically verify our functions against their native counterparts.

#	code	expected result
1	ParseInLocation('2006-01-02 15:04:05', '2026-03-03 13:14:15', 'America/New_York')	new Date('2026-03-03T18:14:15.000Z')
2	ParseInLocation('2006-01-02 15:04:05', '2026-07-03 13:14:15', 'America/New_York')	new Date('2026-07-03T17:14:15.000Z')
3	ParseInLocation('2006-01-02 15:04:05', '2024-11-03 01:30:00', 'America/New_York')	new Date('2024-11-03T05:30:00.000Z')
4	ParseInLocation('2006-01-02 15:04:05', '2024-03-10 02:30:00', 'America/New_York')	new Date('2024-03-10T06:30:00.000Z')
5	ParseInLocation('2006-01-02T15:04:05-07:00', '2026-03-03T13:14:15+02:30', 'America/New_York')	new Date('2026-03-03T10:44:15.000Z')
6	ParseInLocation('2006-01-02 15:04:05', '2026-03-03 13:14:15', ('America' + '/New_York'))	new Date('2026-03-03T18:14:15.000Z')

Notes

• Supports the same focused layout-token subset as Parse.

• Inputs without an explicit numeric offset are interpreted in the supplied IANA time zone.

• Explicit numeric offsets still take precedence over the supplied location, matching Go’s absolute-time result.

Here's what our current TypeScript equivalent to Go's time.ParseInLocation looks like.

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

Copy code

type GoParseToken = (typeof GO_PARSE_TOKENS)[number]

const GO_PARSE_TOKENS = [
  'Z07:00',
  '-07:00',
  '-0700',
  '2006',
  'PM',
  'pm',
  '15',
  '06',
  '01',
  '02',
  '03',
  '04',
  '05',
  '1',
  '2',
  '3',
] as const

type ParsedGoTime = {
  localMillis: number
  hasOffset: boolean
  offsetMinutes: number
}

const escapeRegex = (value: string): string => value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')

const isTokenAt = (layout: string, index: number): GoParseToken | undefined =>
  GO_PARSE_TOKENS.find((token) => layout.startsWith(token, index))

const tokenRegex = (token: GoParseToken): string => {
  switch (token) {
    case '2006':
      return '(\\d{4})'
    case '06':
      return '(\\d{2})'
    case '01':
      return '(0[1-9]|1[0-2])'
    case '1':
      return '([1-9]|1[0-2])'
    case '02':
      return '(0[1-9]|[12]\\d|3[01])'
    case '2':
      return '([1-9]|[12]\\d|3[01])'
    case '15':
      return '([01]\\d|2[0-3])'
    case '03':
      return '(0[1-9]|1[0-2])'
    case '3':
      return '([1-9]|1[0-2])'
    case '04':
      return '([0-5]\\d)'
    case '05':
      return '([0-5]\\d)'
    case 'PM':
      return '(AM|PM)'
    case 'pm':
      return '(am|pm)'
    case '-0700':
      return '([+-]\\d{4})'
    case '-07:00':
      return '([+-]\\d{2}:\\d{2})'
    case 'Z07:00':
      return '(Z|[+-]\\d{2}:\\d{2})'
    default:
      return escapeRegex(token)
  }
}

const parseOffsetMinutes = (offset: string): number => {
  if (offset === 'Z') {
    return 0
  }

  const compact = offset.match(/^([+-])(\d{2})(\d{2})$/)
  if (compact?.[1] && compact[2] && compact[3]) {
    const sign = compact[1] === '-' ? -1 : 1
    const hours = Number.parseInt(compact[2], 10)
    const minutes = Number.parseInt(compact[3], 10)
    if (hours > 23 || minutes > 59) {
      throw new TypeError('ParseInLocation(): invalid offset')
    }
    return sign * (hours * 60 + minutes)
  }

  const colon = offset.match(/^([+-])(\d{2}):(\d{2})$/)
  if (colon?.[1] && colon[2] && colon[3]) {
    const sign = colon[1] === '-' ? -1 : 1
    const hours = Number.parseInt(colon[2], 10)
    const minutes = Number.parseInt(colon[3], 10)
    if (hours > 23 || minutes > 59) {
      throw new TypeError('ParseInLocation(): invalid offset')
    }
    return sign * (hours * 60 + minutes)
  }

  throw new TypeError('ParseInLocation(): invalid offset')
}

const resolveTwoDigitYear = (year: number): number => (year >= 69 ? 1900 + year : 2000 + year)

const createUtcDate = (
  year: number,
  month: number,
  day: number,
  hour: number,
  minute: number,
  second: number,
): Date => {
  const date = new Date(0)
  date.setUTCFullYear(year, month - 1, day)
  date.setUTCHours(hour, minute, second, 0)
  return date
}

const parseGoTime = (layout: string, value: string): ParsedGoTime => {
  const resolvedLayout = String(layout)
  const resolvedValue = String(value)

  const tokenOrder: GoParseToken[] = []
  let regexSource = '^'

  for (let i = 0; i < resolvedLayout.length; ) {
    const token = isTokenAt(resolvedLayout, i)
    if (token) {
      regexSource += tokenRegex(token)
      tokenOrder.push(token)
      i += token.length
      continue
    }

    const char = resolvedLayout[i]
    if (char === undefined) {
      break
    }

    regexSource += escapeRegex(char)
    i += 1
  }

  regexSource += '$'
  const match = new RegExp(regexSource).exec(resolvedValue)
  if (!match) {
    throw new TypeError('ParseInLocation(): input does not match layout')
  }

  let year = 1970
  let month = 1
  let day = 1
  let hour24 = 0
  let minute = 0
  let second = 0
  let hour12: number | undefined
  let ampm: 'AM' | 'PM' | undefined
  let offsetMinutes = 0
  let hasOffset = false

  let matchIndex = 1
  for (const token of tokenOrder) {
    const raw = match[matchIndex]
    matchIndex += 1
    if (!raw) {
      continue
    }

    switch (token) {
      case '2006':
        year = Number.parseInt(raw, 10)
        break
      case '06':
        year = resolveTwoDigitYear(Number.parseInt(raw, 10))
        break
      case '01':
      case '1':
        month = Number.parseInt(raw, 10)
        break
      case '02':
      case '2':
        day = Number.parseInt(raw, 10)
        break
      case '15':
        hour24 = Number.parseInt(raw, 10)
        break
      case '03':
      case '3':
        hour12 = Number.parseInt(raw, 10)
        break
      case '04':
        minute = Number.parseInt(raw, 10)
        break
      case '05':
        second = Number.parseInt(raw, 10)
        break
      case 'PM':
      case 'pm':
        ampm = raw.toUpperCase() === 'PM' ? 'PM' : 'AM'
        break
      case '-0700':
      case '-07:00':
      case 'Z07:00':
        offsetMinutes = parseOffsetMinutes(raw)
        hasOffset = true
        break
      default:
        break
    }
  }

  if (hour12 !== undefined) {
    if (ampm === 'PM' && hour12 < 12) {
      hour24 = hour12 + 12
    } else if (ampm === 'AM' && hour12 === 12) {
      hour24 = 0
    } else {
      hour24 = hour12
    }
  }

  if (
    month < 1 ||
    month > 12 ||
    day < 1 ||
    day > 31 ||
    hour24 < 0 ||
    hour24 > 23 ||
    minute < 0 ||
    minute > 59 ||
    second < 0 ||
    second > 59
  ) {
    throw new TypeError('ParseInLocation(): invalid datetime components')
  }

  const localCheck = createUtcDate(year, month, day, hour24, minute, second)
  if (
    localCheck.getUTCFullYear() !== year ||
    localCheck.getUTCMonth() + 1 !== month ||
    localCheck.getUTCDate() !== day ||
    localCheck.getUTCHours() !== hour24 ||
    localCheck.getUTCMinutes() !== minute ||
    localCheck.getUTCSeconds() !== second
  ) {
    throw new TypeError('ParseInLocation(): invalid datetime components')
  }

  const localMillis = localCheck.getTime()

  return {
    localMillis,
    hasOffset,
    offsetMinutes,
  }
}

const zonedFormatterCache = new Map<string, Intl.DateTimeFormat>()

const getZonedFormatter = (timeZone: string): Intl.DateTimeFormat => {
  let formatter = zonedFormatterCache.get(timeZone)
  if (!formatter) {
    formatter = new Intl.DateTimeFormat('en-CA', {
      timeZone,
      year: 'numeric',
      month: '2-digit',
      day: '2-digit',
      hour: '2-digit',
      minute: '2-digit',
      second: '2-digit',
      hourCycle: 'h23',
    })
    zonedFormatterCache.set(timeZone, formatter)
  }
  return formatter
}

const assertValidLocation = (location: string): void => {
  try {
    getZonedFormatter(location).format(new Date(0))
  } catch {
    throw new TypeError('ParseInLocation(): invalid location')
  }
}

const getOffsetMinutesAt = (timeZone: string, utcMillis: number): number => {
  const formatter = getZonedFormatter(timeZone)
  const parts = formatter.formatToParts(new Date(utcMillis))

  let year = 0
  let month = 1
  let day = 1
  let hour = 0
  let minute = 0
  let second = 0

  for (const part of parts) {
    switch (part.type) {
      case 'year':
        year = Number.parseInt(part.value, 10)
        break
      case 'month':
        month = Number.parseInt(part.value, 10)
        break
      case 'day':
        day = Number.parseInt(part.value, 10)
        break
      case 'hour':
        hour = Number.parseInt(part.value, 10)
        break
      case 'minute':
        minute = Number.parseInt(part.value, 10)
        break
      case 'second':
        second = Number.parseInt(part.value, 10)
        break
      default:
        break
    }
  }

  const zonedAsUtcMillis = createUtcDate(year, month, day, hour, minute, second).getTime()
  return Math.round((zonedAsUtcMillis - utcMillis) / 60_000)
}

const resolveWallTimeInLocation = (timeZone: string, localMillis: number): number => {
  let offsetMinutes = getOffsetMinutesAt(timeZone, localMillis)

  if (offsetMinutes !== 0) {
    const utcMillis = localMillis - offsetMinutes * 60_000
    const correctedOffsetMinutes = getOffsetMinutesAt(timeZone, utcMillis)
    if (correctedOffsetMinutes !== offsetMinutes) {
      offsetMinutes = correctedOffsetMinutes
    }
  }

  return localMillis - offsetMinutes * 60_000
}

export function ParseInLocation(layout: string, value: string, location: string): Date {
  //      discuss at: https://locutus.io/golang/time/ParseInLocation
  // parity verified: Go 1.23
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Supports the same focused layout-token subset as Parse.
  //          note 2: Inputs without an explicit numeric offset are interpreted in the supplied IANA time zone.
  //          note 3: Explicit numeric offsets still take precedence over the supplied location, matching Go's absolute-time result.
  //       example 1: ParseInLocation('2006-01-02 15:04:05', '2026-03-03 13:14:15', 'America/New_York')
  //       returns 1: new Date('2026-03-03T18:14:15.000Z')
  //       example 2: ParseInLocation('2006-01-02 15:04:05', '2026-07-03 13:14:15', 'America/New_York')
  //       returns 2: new Date('2026-07-03T17:14:15.000Z')
  //       example 3: ParseInLocation('2006-01-02 15:04:05', '2024-11-03 01:30:00', 'America/New_York')
  //       returns 3: new Date('2024-11-03T05:30:00.000Z')
  //       example 4: ParseInLocation('2006-01-02 15:04:05', '2024-03-10 02:30:00', 'America/New_York')
  //       returns 4: new Date('2024-03-10T06:30:00.000Z')
  //       example 5: ParseInLocation('2006-01-02T15:04:05-07:00', '2026-03-03T13:14:15+02:30', 'America/New_York')
  //       returns 5: new Date('2026-03-03T10:44:15.000Z')
  //       example 6: ParseInLocation('2006-01-02 15:04:05', '2026-03-03 13:14:15', ('America' + '/New_York'))
  //       returns 6: new Date('2026-03-03T18:14:15.000Z')

  const resolvedLocation = String(location)
  assertValidLocation(resolvedLocation)

  const parsed = parseGoTime(layout, value)
  const utcMillis = parsed.hasOffset
    ? parsed.localMillis - parsed.offsetMinutes * 60_000
    : resolveWallTimeInLocation(resolvedLocation, parsed.localMillis)

  return new Date(utcMillis)
}

const GO_PARSE_TOKENS = [
  'Z07:00',
  '-07:00',
  '-0700',
  '2006',
  'PM',
  'pm',
  '15',
  '06',
  '01',
  '02',
  '03',
  '04',
  '05',
  '1',
  '2',
  '3',
]

const escapeRegex = (value) => value.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')

const isTokenAt = (layout, index) => GO_PARSE_TOKENS.find((token) => layout.startsWith(token, index))

const tokenRegex = (token) => {
  switch (token) {
    case '2006':
      return '(\\d{4})'
    case '06':
      return '(\\d{2})'
    case '01':
      return '(0[1-9]|1[0-2])'
    case '1':
      return '([1-9]|1[0-2])'
    case '02':
      return '(0[1-9]|[12]\\d|3[01])'
    case '2':
      return '([1-9]|[12]\\d|3[01])'
    case '15':
      return '([01]\\d|2[0-3])'
    case '03':
      return '(0[1-9]|1[0-2])'
    case '3':
      return '([1-9]|1[0-2])'
    case '04':
      return '([0-5]\\d)'
    case '05':
      return '([0-5]\\d)'
    case 'PM':
      return '(AM|PM)'
    case 'pm':
      return '(am|pm)'
    case '-0700':
      return '([+-]\\d{4})'
    case '-07:00':
      return '([+-]\\d{2}:\\d{2})'
    case 'Z07:00':
      return '(Z|[+-]\\d{2}:\\d{2})'
    default:
      return escapeRegex(token)
  }
}

const parseOffsetMinutes = (offset) => {
  if (offset === 'Z') {
    return 0
  }

  const compact = offset.match(/^([+-])(\d{2})(\d{2})$/)
  if (compact?.[1] && compact[2] && compact[3]) {
    const sign = compact[1] === '-' ? -1 : 1
    const hours = Number.parseInt(compact[2], 10)
    const minutes = Number.parseInt(compact[3], 10)
    if (hours > 23 || minutes > 59) {
      throw new TypeError('ParseInLocation(): invalid offset')
    }
    return sign * (hours * 60 + minutes)
  }

  const colon = offset.match(/^([+-])(\d{2}):(\d{2})$/)
  if (colon?.[1] && colon[2] && colon[3]) {
    const sign = colon[1] === '-' ? -1 : 1
    const hours = Number.parseInt(colon[2], 10)
    const minutes = Number.parseInt(colon[3], 10)
    if (hours > 23 || minutes > 59) {
      throw new TypeError('ParseInLocation(): invalid offset')
    }
    return sign * (hours * 60 + minutes)
  }

  throw new TypeError('ParseInLocation(): invalid offset')
}

const resolveTwoDigitYear = (year) => (year >= 69 ? 1900 + year : 2000 + year)

const createUtcDate = (year, month, day, hour, minute, second) => {
  const date = new Date(0)
  date.setUTCFullYear(year, month - 1, day)
  date.setUTCHours(hour, minute, second, 0)
  return date
}

const parseGoTime = (layout, value) => {
  const resolvedLayout = String(layout)
  const resolvedValue = String(value)

  const tokenOrder = []
  let regexSource = '^'

  for (let i = 0; i < resolvedLayout.length; ) {
    const token = isTokenAt(resolvedLayout, i)
    if (token) {
      regexSource += tokenRegex(token)
      tokenOrder.push(token)
      i += token.length
      continue
    }

    const char = resolvedLayout[i]
    if (char === undefined) {
      break
    }

    regexSource += escapeRegex(char)
    i += 1
  }

  regexSource += '$'
  const match = new RegExp(regexSource).exec(resolvedValue)
  if (!match) {
    throw new TypeError('ParseInLocation(): input does not match layout')
  }

  let year = 1970
  let month = 1
  let day = 1
  let hour24 = 0
  let minute = 0
  let second = 0
  let hour12
  let ampm
  let offsetMinutes = 0
  let hasOffset = false

  let matchIndex = 1
  for (const token of tokenOrder) {
    const raw = match[matchIndex]
    matchIndex += 1
    if (!raw) {
      continue
    }

    switch (token) {
      case '2006':
        year = Number.parseInt(raw, 10)
        break
      case '06':
        year = resolveTwoDigitYear(Number.parseInt(raw, 10))
        break
      case '01':
      case '1':
        month = Number.parseInt(raw, 10)
        break
      case '02':
      case '2':
        day = Number.parseInt(raw, 10)
        break
      case '15':
        hour24 = Number.parseInt(raw, 10)
        break
      case '03':
      case '3':
        hour12 = Number.parseInt(raw, 10)
        break
      case '04':
        minute = Number.parseInt(raw, 10)
        break
      case '05':
        second = Number.parseInt(raw, 10)
        break
      case 'PM':
      case 'pm':
        ampm = raw.toUpperCase() === 'PM' ? 'PM' : 'AM'
        break
      case '-0700':
      case '-07:00':
      case 'Z07:00':
        offsetMinutes = parseOffsetMinutes(raw)
        hasOffset = true
        break
      default:
        break
    }
  }

  if (hour12 !== undefined) {
    if (ampm === 'PM' && hour12 < 12) {
      hour24 = hour12 + 12
    } else if (ampm === 'AM' && hour12 === 12) {
      hour24 = 0
    } else {
      hour24 = hour12
    }
  }

  if (
    month < 1 ||
    month > 12 ||
    day < 1 ||
    day > 31 ||
    hour24 < 0 ||
    hour24 > 23 ||
    minute < 0 ||
    minute > 59 ||
    second < 0 ||
    second > 59
  ) {
    throw new TypeError('ParseInLocation(): invalid datetime components')
  }

  const localCheck = createUtcDate(year, month, day, hour24, minute, second)
  if (
    localCheck.getUTCFullYear() !== year ||
    localCheck.getUTCMonth() + 1 !== month ||
    localCheck.getUTCDate() !== day ||
    localCheck.getUTCHours() !== hour24 ||
    localCheck.getUTCMinutes() !== minute ||
    localCheck.getUTCSeconds() !== second
  ) {
    throw new TypeError('ParseInLocation(): invalid datetime components')
  }

  const localMillis = localCheck.getTime()

  return {
    localMillis,
    hasOffset,
    offsetMinutes,
  }
}

const zonedFormatterCache = new Map()

const getZonedFormatter = (timeZone) => {
  let formatter = zonedFormatterCache.get(timeZone)
  if (!formatter) {
    formatter = new Intl.DateTimeFormat('en-CA', {
      timeZone,
      year: 'numeric',
      month: '2-digit',
      day: '2-digit',
      hour: '2-digit',
      minute: '2-digit',
      second: '2-digit',
      hourCycle: 'h23',
    })
    zonedFormatterCache.set(timeZone, formatter)
  }
  return formatter
}

const assertValidLocation = (location) => {
  try {
    getZonedFormatter(location).format(new Date(0))
  } catch {
    throw new TypeError('ParseInLocation(): invalid location')
  }
}

const getOffsetMinutesAt = (timeZone, utcMillis) => {
  const formatter = getZonedFormatter(timeZone)
  const parts = formatter.formatToParts(new Date(utcMillis))

  let year = 0
  let month = 1
  let day = 1
  let hour = 0
  let minute = 0
  let second = 0

  for (const part of parts) {
    switch (part.type) {
      case 'year':
        year = Number.parseInt(part.value, 10)
        break
      case 'month':
        month = Number.parseInt(part.value, 10)
        break
      case 'day':
        day = Number.parseInt(part.value, 10)
        break
      case 'hour':
        hour = Number.parseInt(part.value, 10)
        break
      case 'minute':
        minute = Number.parseInt(part.value, 10)
        break
      case 'second':
        second = Number.parseInt(part.value, 10)
        break
      default:
        break
    }
  }

  const zonedAsUtcMillis = createUtcDate(year, month, day, hour, minute, second).getTime()
  return Math.round((zonedAsUtcMillis - utcMillis) / 60_000)
}

const resolveWallTimeInLocation = (timeZone, localMillis) => {
  let offsetMinutes = getOffsetMinutesAt(timeZone, localMillis)

  if (offsetMinutes !== 0) {
    const utcMillis = localMillis - offsetMinutes * 60_000
    const correctedOffsetMinutes = getOffsetMinutesAt(timeZone, utcMillis)
    if (correctedOffsetMinutes !== offsetMinutes) {
      offsetMinutes = correctedOffsetMinutes
    }
  }

  return localMillis - offsetMinutes * 60_000
}

export function ParseInLocation(layout, value, location) {
  //      discuss at: https://locutus.io/golang/time/ParseInLocation
  // parity verified: Go 1.23
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Supports the same focused layout-token subset as Parse.
  //          note 2: Inputs without an explicit numeric offset are interpreted in the supplied IANA time zone.
  //          note 3: Explicit numeric offsets still take precedence over the supplied location, matching Go's absolute-time result.
  //       example 1: ParseInLocation('2006-01-02 15:04:05', '2026-03-03 13:14:15', 'America/New_York')
  //       returns 1: new Date('2026-03-03T18:14:15.000Z')
  //       example 2: ParseInLocation('2006-01-02 15:04:05', '2026-07-03 13:14:15', 'America/New_York')
  //       returns 2: new Date('2026-07-03T17:14:15.000Z')
  //       example 3: ParseInLocation('2006-01-02 15:04:05', '2024-11-03 01:30:00', 'America/New_York')
  //       returns 3: new Date('2024-11-03T05:30:00.000Z')
  //       example 4: ParseInLocation('2006-01-02 15:04:05', '2024-03-10 02:30:00', 'America/New_York')
  //       returns 4: new Date('2024-03-10T06:30:00.000Z')
  //       example 5: ParseInLocation('2006-01-02T15:04:05-07:00', '2026-03-03T13:14:15+02:30', 'America/New_York')
  //       returns 5: new Date('2026-03-03T10:44:15.000Z')
  //       example 6: ParseInLocation('2006-01-02 15:04:05', '2026-03-03 13:14:15', ('America' + '/New_York'))
  //       returns 6: new Date('2026-03-03T18:14:15.000Z')

  const resolvedLocation = String(location)
  assertValidLocation(resolvedLocation)

  const parsed = parseGoTime(layout, value)
  const utcMillis = parsed.hasOffset
    ? parsed.localMillis - parsed.offsetMinutes * 60_000
    : resolveWallTimeInLocation(resolvedLocation, parsed.localMillis)

  return new Date(utcMillis)
}

Improve this function

Locutus is a community effort following The McDonald's Theory: we ship first iterations, hoping others will improve them. If you see something that could be better, we'd love your contribution.

View on GitHub · Edit on GitHub · View Raw

---

Help us add more

Got a rainy Sunday afternoon and a taste for a porting puzzle?

• Get inspiration from Go strings documentation, Go strings source, Go strings examples source, GopherJS.
• Click "New file" in the appropriate folder on GitHub. This will fork the project to your account, directly add the file to it, and send a Pull Request to us.

We will then review it. If it's useful to the project and in line with our contributing guidelines your work will become part of Locutus and you'll be automatically credited in the authors section accordingly.

« More Go time functions

Star