TZDate class toISOString() method not returning correct ISO format

[krema]

The toISOString() method of the TZDate class is not returning the correct output. According to the ISO 8601 standard, the toISOString() method should return a string in the format YYYY-MM-DDTHH:mm:ss.sssZ, where the timezone is always UTC, denoted by the suffix Z.

See: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString

Current Behavior: The method currently returns:

// 2023-05-12T12:00:00.000+02:00    
new TZDate(2023, 4, 12, 12, 0, 0, 'Europe/Berlin').toISOString()

Please note that the format is wrong

Expected Behavior: The method should return (I'm located in 'Europe/Berlin') :

// 2023-05-12T10:00:00.000Z
new Date(2023, 4, 12, 12, 0, 0).toISOString()

I'm using v1.1.1

[johnny-T]

Hi, I am running into this issue as well in version 1.1.2. Not only the toISOString() method, but also the toJSON() method formats the time not in UTC but in local TZ.

[janneh]

Same here. Also expected it to follow the ISO 8601 standard and that this should hold:

test("toISOString", () => {
  const sg = new TZDate(2022, 2, 13, "Asia/Singapore")
  const ny = sg.withTimeZone("America/New_York")

  expect(
    sg.toISOString()
  ).toBe(
    ny.toISOString()
  )
})

but currently results in:

+ Expected: "2022-03-12T11:00:00.000-05:00"
- Received: "2022-03-13T00:00:00.000+08:00"

[ianawilson]

Same on tz 1.1.2 and date-fns 4.1.0. I'm working around this with formatISO(date, {in: tz("UTC")}) to force it to UTC format