Incompatibility with @formatjs/datetimeformat polyfill

[Titozzz]

When polyfilling Intl.DateTimeFormat with @formatjs/datetimeformat and using tzOffset, 2 issues arise:

https://github.com/formatjs/formatjs/blob/main/packages/ecma402-abstract/IsValidTimeZoneName.ts#L6
https://github.com/date-fns/tz/blob/main/src/tzOffset/index.ts#L20

1. The timezone format isn't supported by the polyfill (that is supposed to cover 100% of the spec),
   -> So who's correct ? Does the format here or there needs fixing ?

2. The cache that's added to prevent performance issues is not working when the method throws, so it will try to recreate a new format function on every call, harming performance seriously when using a JS engine that is slow regarding Intl APIs (hermes on react native)

Fixing 1) would mean 2) doesn't affect me anymore but we could still address the issue to not retry and crash everytime.

I'm open to addressing those issues in a PR, but just making just we are aligned first, thanks!

Linked issue in the other repo: formatjs/formatjs#4804

[ryaa]

@Titozzz as I understand the error happens because timeZoneName: "longOffset" which is not supported on iOS 15.4 or below (see https://github.com/date-fns/tz/blob/main/src/tzOffset/index.ts#L22). More details can be found #23 (comment)

[Titozzz]

Yes iOS 15.4 or below has that issue, but the polyfill is supposed to address that, as it is supposed to fill the gaps to match the spec. Here the issue that I'm pointing at is that even the polyfill doesn't fix the issue, which mean that either the polyfill or this library is wrong

[ryaa]

but the polyfill is supposed to address that, as it is supposed to fill the gaps to match the spec

exactly. This is the polyfill issue.

[ryaa]

Until formatjs polyfills is fixed to correctly handle the above use case, I implemented a temporary fix for date-fns/tz package - see #23 (comment)

I can create a PR for date-fns/tz based on my temporary fix but I believe that this must be fixed in formatjs