Non-valid .toISOString(), must include 'Z' at the end

[warmrobot]

https://github.com/date-fns/tz/blob/main/src/date/index.js#L29-L30

And there is no seconds, by the way

[GianlucaWassermeyer]

Hello,

The 'Z' indicates that the ISOString is in Zulu time (UTC). He uses the variant with the timezone offset inside the ISOString for TZDate, which is just as valid as the other format. Furthermore, JavaScript Date does not accept any timezone offsets with seconds; it would be an invalid ISOString.

[sovcik]

Well, as format is is valid to have both "Z" and "+00:00", but it differs from what Javascript toISOString should do:

1. datetime is always UTC
2. suffix is always "Z"
   see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toISOString

I actually like TZDate approach more - never really understood why toISOString changes timezone too, but that's how it is... and if TZDate's goal is to be fully compatible, then this should be fixed.

[GianlucaWassermeyer]

If you don´t like the toISOString() from TZDate, you can use TZDateMini as a workaround. That´s what I use in my project to always return an ISOString with Z.