@posthog/types/src/feature-flags.ts

Type definitions for the PostHog JavaScript SDK

/**
 * Feature flag types
 */

import type { JsonType } from './common'

export type FeatureFlagsCallback = (
    flags: string[],
    variants: Record<string, string | boolean>,
    context?: {
        errorsLoading?: boolean
    }
) => void

export type FeatureFlagDetail = {
    key: string
    enabled: boolean
    // Only used when overriding a flag payload.
    original_enabled?: boolean | undefined
    variant: string | undefined
    // Only used when overriding a flag payload.
    original_variant?: string | undefined
    reason: EvaluationReason | undefined
    metadata: FeatureFlagMetadata | undefined
    failed?: boolean
}

export type FeatureFlagMetadata = {
    id: number
    version: number | undefined
    description: string | undefined
    payload: JsonType | undefined
    /** Whether the flag is linked to an experiment. Absent when the server does not report it. */
    has_experiment?: boolean
    // Only used when overriding a flag payload.
    original_payload?: JsonType | undefined
}

export type EvaluationReason = {
    code: string
    condition_index: number | undefined
    description: string | undefined
}

export type RemoteConfigFeatureFlagCallback = (payload: JsonType) => void

// Sync this with the backend's EarlyAccessFeatureSerializer!
/** A feature that isn't publicly available yet.*/
export interface EarlyAccessFeature {
    name: string
    description: string
    stage: 'concept' | 'alpha' | 'beta'
    documentationUrl: string | null
    payload: JsonType
    flagKey: string | null
}

export type EarlyAccessFeatureStage = 'concept' | 'alpha' | 'beta' | 'general-availability'
export type EarlyAccessFeatureCallback = (earlyAccessFeatures: EarlyAccessFeature[]) => void

/**
 * Result of evaluating a feature flag, including both the flag value and its payload.
 */
export type FeatureFlagResult = {
    /** The key of the feature flag */
    readonly key: string
    /** Whether the feature flag is enabled (truthy value) */
    readonly enabled: boolean
    /** The variant key if this is a multivariate flag, undefined for boolean flags */
    readonly variant: string | undefined
    /** The JSON payload associated with this flag, if any */
    readonly payload: JsonType | undefined
}

export interface EarlyAccessFeatureResponse {
    earlyAccessFeatures: EarlyAccessFeature[]
}

export type FeatureFlagOverrides = {
    [flagName: string]: string | boolean
}

export type FeatureFlagPayloadOverrides = {
    [flagName: string]: JsonType
}

export type FeatureFlagOverrideOptions = {
    flags?: boolean | string[] | FeatureFlagOverrides
    payloads?: FeatureFlagPayloadOverrides
    suppressWarning?: boolean
}

/**
 * Options for feature flag lookup methods (getFeatureFlag, isFeatureEnabled, getFeatureFlagResult).
 */
export type FeatureFlagOptions = {
    /**
     * Whether to send a $feature_flag_called event. Defaults to true.
     */
    send_event?: boolean
    /**
     * If true, only return values loaded from the server, not cached localStorage values.
     * Returns undefined if flags haven't been loaded from the server yet.
     * Defaults to false.
     */
    fresh?: boolean
}

/**
 * Options for isFeatureEnabled.
 */
export type IsFeatureEnabledOptions = FeatureFlagOptions & {
    /**
     * Value to return when the flag has no value, e.g. flags have not loaded yet or no flag with that key exists.
     */
    defaultValue?: boolean
}

/**
 * Options for overriding feature flags on the client-side.
 *
 * Can be:
 * - `false` to clear all overrides
 * - `string[]` to enable a list of flags
 * - `FeatureFlagOverrides` to set variants directly
 * - `FeatureFlagOverrideOptions` for granular control over flags and payloads
 */
export type OverrideFeatureFlagsOptions =
    | boolean // clear all overrides
    | string[] // enable list of flags
    | FeatureFlagOverrides // set variants directly
    | FeatureFlagOverrideOptions