Flags SDK: Missing documentation details for Posthog

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1

I am trying to setup feature flags via the flags sdk with the posthog provider.

Defining

export const myTestFlag = flag({
  key: "my-test-flag",
  adapter: postHogAdapter.isFeatureEnabled(),
});

is valid and TypeScript doesn’t complain.

However it will throw an error:

Error: PostHog Adapter: Missing entities, flag must be defined with an identify() function.

In the docs this is simple referred to as:

import identify from "@/lib/identify";
 
export const myFlag = flag({
  key: "posthog-is-feature-enabled",
  adapter: postHogAdapter.isFeatureEnabled(),
  identify,
});

with no details how the identify function has to be implemented.

Adding an async function that returns the email as string or as an object {email: string} will lead to an error on the adapter:

image
image2954×842 236 KB

After a while of digging it seems identify should return Promise<{distinctId: string}> . This would be a valuable addition to the docs as it’s not obvious.

Additionally when a feature-flag is disabled in PostHog and the feature flag is implemented as shown in the docs this will lead to following error:

Error: PostHog Adapter isFeatureEnabled returned undefined for my-test-flag and no default value was provided.

hence the documentation should contain the defaultValue:

export const myTestFlag = flag({
  key: "my-test-flag",
  defaultValue: false,
  adapter: postHogAdapter.isFeatureEnabled(),
  identify,
});
4

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