feat(feature-flags): Add bootstrap option for feature flags

[neilkakkar]

Just like PostHog/posthog-js#444 but for react-native.

@benjackwhite I could use some help figuring out this works for react-native.

Current issues I'm facing:

1. The CI doesn't seem to be testing posthog-react-native ?
2. How do I get the new test created specifically for react-native to run? Unfamiliar with expo, and it's complaining about those imports.
3. Can you help testing a 'live' version of this and confirming it works?

[benjackwhite]

1. The CI doesn't seem to be testing `posthog-react-native` ?

It does - It's right after the standard tests https://github.com/PostHog/posthog-js-lite/blob/master/.github/workflows/ci.yml#L22

2. How do I get the new test created specifically for react-native to run? Unfamiliar with expo, and it's complaining about those imports.

Expo is a hard beast to test but for this we can stick to the unit tests. They have to be run separate to the other tests due to some specific tsconfig rules for React Native...

3. Can you help testing a 'live' version of this and confirming it works?

Sure - I'll check it out!

[benjackwhite]

@neilkakkar trying to fix the tests but not sure what the logic should be.
Currently its doing this:

1. On load bootstrap the things
2. If feature flags are given they are set 👍
3. Immediately after we reload the feature flags

My assumption is we don't want to immediately reload the flags from the API if they are given. Is that correct?

[neilkakkar]

My assumption is we don't want to immediately reload the flags from the API if they are given. Is that correct?

No, this is okay!

The idea is that some flags are available on immediate load, while we wait for /decide or new properties to reflect in the feature flags.
Some flags would be impossible to bootstrap, hence the immediate reload ensures we get those as soon as possible as well.

[benjackwhite]

@neilkakkar this looks good now and everything passes. Turns out memorystorage for RN was always broken anyway so this is a good catch...

Might be worth a quick glance for yourself over what I changed but if that's all good then I'd say we are good to go

[neilkakkar]

Much appreciated, thanks! I just added a test for the async storage as well.