feat(browser): Tree shake feature flags#3166
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marandaneto
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Move PostHogFeatureFlags to conditional construction via __extensionClasses. When not included in the bundle, a proxy stub provides graceful degradation with no-op methods. Bootstrap flag logic is moved from posthog-core into PostHogFeatureFlags.initialize(). The updateFlags() method is added to encapsulate flag injection logic previously in posthog-core.
This closes a behavioral gap where `.featureFlags` would return a stub before `init()` is called
- So we can mangle it - Because `featureFlags` should always be available anyway
Still somewhat experimental, but annoying as it can't be disabled.
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Problem
PostHogFeatureFlagsis always constructed in the PostHog constructor and deeply referenced throughout posthog-core. It's the largest remaining class that can't be excluded from custom bundles, but it's also the most pervasive, so making it optional requires careful handling of every call site.This is PR 3/3
Changes
Makes
PostHogFeatureFlagstree-shakable via__extensionClasseswith a Proxy-based stub for graceful degradation.posthog-featureflags-stub.ts): When FeatureFlags isn't in the bundle,this.featureFlagsreturns a Proxy that logs an error and returns no-op values for any method call. This avoids crashes or unexpected behavior without requiring optional chaining at every call site (esp. considering end-user code may expect these calls to work)._featureFlags?is the real property;get featureFlags()returns the instance or the stub. Internal code that needs to distinguish "not loaded" from "loaded" uses_featureFlagsdirectly. This is necessary because it allows us to avoid changing thePostHogInterface(i.e., a breaking change).posthog-core._init()intoPostHogFeatureFlags.initialize(), keeping feature-flag-specific logic in its own class (and tree-shakable).updateFlags()method: Flag injection logic moved fromposthog-core.setFeatureFlags()into the FeatureFlags class. Similar reasoning to above.FeatureFlagsExtensionsadded. Bundles that depend on flags (ProductToursExtensions,SurveysExtensions,ExperimentsExtensions) spread...FeatureFlagsExtensionsso flags are automatically included.Bundle size
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