Go's time.Format in TypeScript

How to use

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

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

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	Format('2026-03-03T13:14:15.000Z', '2006-01-02')	'2026-03-03'
2	Format('2026-03-03T13:14:15.000Z', '15:04:05')	'13:14:15'
3	Format('2026-03-03T13:14:15.000Z', '01/02/06 03:04 PM')	'03/03/26 01:14 PM'
4	Format('2026-03-03T13:14:15.000Z', 'Z07:00')	'Z'
5	Format('2026-03-03T13:14:15.000Z', '-07:00')	'+00:00'

Notes

• Supports a focused subset of Go layout tokens and formats in UTC for deterministic output. Unsupported layout markers are treated as literals.

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

TSTypeScript JSJavaScript TSStandalone TS JSStandalone JS

Copy code

type DateInput = Date | string | number

type GoLayoutToken = (typeof GO_LAYOUT_TOKENS)[number]

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

const pad2 = (value: number): string => String(value).padStart(2, '0')

const formatToken = (token: GoLayoutToken, date: Date): string => {
  const year = date.getUTCFullYear()
  const month = date.getUTCMonth() + 1
  const day = date.getUTCDate()
  const hour24 = date.getUTCHours()
  const hour12 = hour24 % 12 || 12

  switch (token) {
    case '2006':
      return String(year)
    case '06':
      return pad2(year % 100)
    case '01':
      return pad2(month)
    case '1':
      return String(month)
    case '02':
      return pad2(day)
    case '2':
      return String(day)
    case '15':
      return pad2(hour24)
    case '03':
      return pad2(hour12)
    case '3':
      return String(hour12)
    case '04':
      return pad2(date.getUTCMinutes())
    case '05':
      return pad2(date.getUTCSeconds())
    case 'PM':
      return hour24 >= 12 ? 'PM' : 'AM'
    case 'pm':
      return hour24 >= 12 ? 'pm' : 'am'
    case '-0700':
      return '+0000'
    case '-07:00':
      return '+00:00'
    case 'Z07:00':
      return 'Z'
    default:
      return token
  }
}

const toUtcDate = (value: DateInput): Date => {
  const date = value instanceof Date ? new Date(value.getTime()) : new Date(value)

  if (Number.isNaN(date.getTime())) {
    throw new TypeError('Format(): invalid date input')
  }

  return date
}

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

export function Format(value: DateInput, layout: string): string {
  //      discuss at: https://locutus.io/golang/time/Format
  // parity verified: Go 1.23
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Supports a focused subset of Go layout tokens and formats in UTC for deterministic output.
  //          note 1: Unsupported layout markers are treated as literals.
  //       example 1: Format('2026-03-03T13:14:15.000Z', '2006-01-02')
  //       returns 1: '2026-03-03'
  //       example 2: Format('2026-03-03T13:14:15.000Z', '15:04:05')
  //       returns 2: '13:14:15'
  //       example 3: Format('2026-03-03T13:14:15.000Z', '01/02/06 03:04 PM')
  //       returns 3: '03/03/26 01:14 PM'
  //       example 4: Format('2026-03-03T13:14:15.000Z', 'Z07:00')
  //       returns 4: 'Z'
  //       example 5: Format('2026-03-03T13:14:15.000Z', '-07:00')
  //       returns 5: '+00:00'

  const date = toUtcDate(value)
  const resolvedLayout = String(layout)
  let result = ''

  for (let i = 0; i < resolvedLayout.length; ) {
    const token = isTokenAt(resolvedLayout, i)
    if (token) {
      result += formatToken(token, date)
      i += token.length
      continue
    }

    const char = resolvedLayout[i]
    if (char === undefined) {
      break
    }
    result += char
    i += 1
  }

  return result
}

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

const pad2 = (value) => String(value).padStart(2, '0')

const formatToken = (token, date) => {
  const year = date.getUTCFullYear()
  const month = date.getUTCMonth() + 1
  const day = date.getUTCDate()
  const hour24 = date.getUTCHours()
  const hour12 = hour24 % 12 || 12

  switch (token) {
    case '2006':
      return String(year)
    case '06':
      return pad2(year % 100)
    case '01':
      return pad2(month)
    case '1':
      return String(month)
    case '02':
      return pad2(day)
    case '2':
      return String(day)
    case '15':
      return pad2(hour24)
    case '03':
      return pad2(hour12)
    case '3':
      return String(hour12)
    case '04':
      return pad2(date.getUTCMinutes())
    case '05':
      return pad2(date.getUTCSeconds())
    case 'PM':
      return hour24 >= 12 ? 'PM' : 'AM'
    case 'pm':
      return hour24 >= 12 ? 'pm' : 'am'
    case '-0700':
      return '+0000'
    case '-07:00':
      return '+00:00'
    case 'Z07:00':
      return 'Z'
    default:
      return token
  }
}

const toUtcDate = (value) => {
  const date = value instanceof Date ? new Date(value.getTime()) : new Date(value)

  if (Number.isNaN(date.getTime())) {
    throw new TypeError('Format(): invalid date input')
  }

  return date
}

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

export function Format(value, layout) {
  //      discuss at: https://locutus.io/golang/time/Format
  // parity verified: Go 1.23
  //     original by: Kevin van Zonneveld (https://kvz.io)
  //          note 1: Supports a focused subset of Go layout tokens and formats in UTC for deterministic output.
  //          note 1: Unsupported layout markers are treated as literals.
  //       example 1: Format('2026-03-03T13:14:15.000Z', '2006-01-02')
  //       returns 1: '2026-03-03'
  //       example 2: Format('2026-03-03T13:14:15.000Z', '15:04:05')
  //       returns 2: '13:14:15'
  //       example 3: Format('2026-03-03T13:14:15.000Z', '01/02/06 03:04 PM')
  //       returns 3: '03/03/26 01:14 PM'
  //       example 4: Format('2026-03-03T13:14:15.000Z', 'Z07:00')
  //       returns 4: 'Z'
  //       example 5: Format('2026-03-03T13:14:15.000Z', '-07:00')
  //       returns 5: '+00:00'

  const date = toUtcDate(value)
  const resolvedLayout = String(layout)
  let result = ''

  for (let i = 0; i < resolvedLayout.length; ) {
    const token = isTokenAt(resolvedLayout, i)
    if (token) {
      result += formatToken(token, date)
      i += token.length
      continue
    }

    const char = resolvedLayout[i]
    if (char === undefined) {
      break
    }
    result += char
    i += 1
  }

  return result
}

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

---

We have 47 Go functions so far - 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