Interface LDClient

Readonlylogger

addHook

• addHook(hook: Hook): void

  Add a hook to the client. In order to register a hook before the client starts, please use the hooks property of LDOptions.

  Hooks provide entrypoints which allow for observation of SDK functions.

  Parameters

  • hook: Hook

    The hook to add.

  Returns void

allFlags

• allFlags(): LDFlagSet

  Returns a map of all available flags to the current context's values.

  Returns LDFlagSet

  An object in which each key is a feature flag key and each value is the flag value. Note that there is no way to specify a default value for each flag as there is with variation, so any flag that cannot be evaluated will be undefined.

boolVariation

• boolVariation(key: string, defaultValue: boolean): boolean

  Determines the boolean variation of a feature flag.

  If the flag variation does not have a boolean value, defaultValue is returned.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: boolean

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns boolean

  The boolean value.

boolVariationDetail

• boolVariationDetail(
      key: string,
      defaultValue: boolean,
  ): LDEvaluationDetailTyped<boolean>

  Determines the boolean variation of a feature flag, along with information about how it was calculated.

  The reason property of the result will also be included in analytics events, if you are capturing detailed event data for this flag.

  If the flag variation does not have a boolean value, defaultValue is returned. The reason will indicate an error of the type WRONG_KIND in this case.

  For more information, see the SDK reference guide.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: boolean

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns LDEvaluationDetailTyped<boolean>

  The result (as an ).

close

• close(): Promise<void>

  Shuts down the client and releases its resources, after delivering any pending analytics events.

  Returns Promise<void>

flush

• flush(): Promise<{ error?: Error; result: boolean }>

  Flushes all pending analytics events.

  Normally, batches of events are delivered in the background at intervals determined by the flushInterval property of LDOptions. Calling flush() triggers an immediate delivery.

  Returns Promise<{ error?: Error; result: boolean }>

  A Promise which resolves once flushing is finished. You can inspect the result of the flush for errors.

getContext

• getContext(): platform.LDContext | undefined

  Returns the client's current context.

  This is the context that was most recently passed to identify, or, if identify has never been called, this will be undefined.

  Returns platform.LDContext | undefined

identify

• identify(context: LDContext, identifyOptions?: LDIdentifyOptions): Promise<void>

  Identifies a context to LaunchDarkly.

  Unlike the server-side SDKs, the client-side JavaScript SDKs maintain a current context state, which is set when you call identify().

  Changing the current context also causes all feature flag values to be reloaded. Until that has finished, calls to variation will still return flag values for the previous context. You can await the Promise to determine when the new flag values are available.

  If used with the sheddable option set to true, then the identify operation will be sheddable. This means that if multiple identify operations are done, without waiting for the previous one to complete, then intermediate operations may be discarded.

  Parameters

  • context: LDContext

    The LDContext object.

  • OptionalidentifyOptions: LDIdentifyOptions

    Optional configuration. Please see LDIdentifyOptions.

  Returns Promise<void>

  A Promise which resolves when the flag values for the specified context are available. It rejects when:

  1. The context is unspecified or has no key.

  2. The identify timeout is exceeded. In client SDKs this defaults to 5s. You can customize this timeout with identifyOptions.

  3. A network error is encountered during initialization.

jsonVariation

• jsonVariation(key: string, defaultValue: unknown): unknown

  Determines the json variation of a feature flag.

  This version may be favored in TypeScript versus variation because it returns an unknown type instead of any. unknown will require a cast before usage.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: unknown

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns unknown

  The json value.

jsonVariationDetail

• jsonVariationDetail(
      key: string,
      defaultValue: unknown,
  ): LDEvaluationDetailTyped<unknown>

  Determines the json variation of a feature flag, along with information about how it was calculated.

  The reason property of the result will also be included in analytics events, if you are capturing detailed event data for this flag.

  This version may be favored in TypeScript versus variation because it returns an unknown type instead of any. unknown will require a cast before usage.

  For more information, see the SDK reference guide.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: unknown

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns LDEvaluationDetailTyped<unknown>

  The result (as an ).

numberVariation

• numberVariation(key: string, defaultValue: number): number

  Determines the numeric variation of a feature flag.

  If the flag variation does not have a numeric value, defaultValue is returned.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: number

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns number

  The numeric value.

numberVariationDetail

• numberVariationDetail(
      key: string,
      defaultValue: number,
  ): LDEvaluationDetailTyped<number>

  Determines the numeric variation of a feature flag for a context, along with information about how it was calculated.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: number

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns LDEvaluationDetailTyped<number>

  The result (as an ).

  Remarks

  The reason property of the result will also be included in analytics events, if you are capturing detailed event data for this flag.

  If the flag variation does not have a numeric value, defaultValue is returned. The reason will indicate an error of the type WRONG_KIND in this case.

  For more information, see the SDK reference guide.

off

• off(key: string, callback: (...args: any[]) => void): void

  Removes an event listener. See on for the available event types.

  Parameters

  • key: string

    The name of the event for which to stop listening.

  • callback: (...args: any[]) => void

    The function to deregister.

  Returns void

on

• on(key: string, callback: (...args: any[]) => void): void

  Registers an event listener.

  Parameters

  • key: string

    The name of the event for which to listen.

  • callback: (...args: any[]) => void

    The function to execute when the event fires. The callback may or may not receive parameters, depending on the type of event.

  Returns void

  Remarks

  You can subscribe to one of the supported EventName:

  • "change": The client has received new feature flag data. This can happen either because you have switched contexts with identify, or because the client has a stream connection and has received a live change to a flag value (see below). The callback parameters are the context and an array of flag keys that have changed.

  • "error": General event for any kind of error condition during client operation. The callback parameters are the context and an Error object. Errors are also output by the logger at the error level.

  • "dataSourceStatus": Event indicating that there has been a change in the status of the data source. This will include the state of the data source as well any error information.

stringVariation

• stringVariation(key: string, defaultValue: string): string

  Determines the string variation of a feature flag.

  If the flag variation does not have a string value, defaultValue is returned.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: string

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns string

  The string value.

stringVariationDetail

• stringVariationDetail(
      key: string,
      defaultValue: string,
  ): LDEvaluationDetailTyped<string>

  Determines the string variation of a feature flag for a context, along with information about how it was calculated.

  Parameters

  • key: string

    The unique key of the feature flag.

  • defaultValue: string

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns LDEvaluationDetailTyped<string>

  The result (as an ).

  Remarks

  The reason property of the result will also be included in analytics events, if you are capturing detailed event data for this flag.

  If the flag variation does not have a string value, defaultValue is returned. The reason will indicate an error of the type WRONG_KIND in this case.

  For more information, see the SDK reference guide.

track

• track(key: string, data?: any, metricValue?: number): void

  Track events for experiments.

  Parameters

  • key: string

    The name of the event, which may correspond to a goal in an experiment.

  • Optionaldata: any

    Additional information to associate with the event.

  • OptionalmetricValue: number

    An optional numeric value that can be used by the LaunchDarkly experimentation feature in numeric custom metrics. Can be omitted if this event is used by only non-numeric metrics. This field will also be returned as part of the custom event for Data Export.

  Returns void

variation

• variation(key: string, defaultValue?: any): any

  We recommend using strongly typed variation methods which perform type checks and handle type errors.

  Parameters

  • key: string

    The unique key of the feature flag.

  • OptionaldefaultValue: any

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns any

  The flag's value.

  Remarks

  Determines the variation of a feature flag.

  In the client-side JavaScript SDKs, this is always a fast synchronous operation because all of the feature flag values for the current context have already been loaded into memory.

variationDetail

• variationDetail(key: string, defaultValue?: any): LDEvaluationDetail

  We recommend using strongly typed variation detail methods which perform type checks and handle type errors.

  Parameters

  • key: string

    The unique key of the feature flag.

  • OptionaldefaultValue: any

    The default value of the flag, to be used if the value is not available from LaunchDarkly.

  Returns LDEvaluationDetail

  An LDEvaluationDetail object containing the value and explanation.

  Remarks

  Determines the variation of a feature flag for a context, along with information about how it was calculated.

  Note that this will only work if you have set withReasons to true in LDOptions.

  The reason property of the result will also be included in analytics events, if you are capturing detailed event data for this flag.

  For more information, see the SDK reference guide.

waitForInitialization

• waitForInitialization(
      options?: LDWaitForInitializationOptions,
  ): Promise<LDWaitForInitializationResult>

  Returns a Promise that tracks the client's initialization state.

  The Promise will be resolved to a LDWaitForInitializationResult object containing the status of the waitForInitialization operation.

  Parameters

  • Optionaloptions: LDWaitForInitializationOptions

    Optional configuration. Please see LDWaitForInitializationOptions.

  Returns Promise<LDWaitForInitializationResult>

  A Promise that will be resolved to a LDWaitForInitializationResult object containing the status of the waitForInitialization operation.

  Example

  This example shows use of async/await syntax for specifying handlers:

      const result = await client.waitForInitialization({ timeout: 5 });
  
      if (result.status === 'complete') {
        doSomethingWithSuccessfullyInitializedClient();
      } else if (result.status === 'failed') {
        doSomethingForFailedStartup(result.error);
      } else if (result.status === 'timeout') {
        doSomethingForTimedOutStartup();
      }
  Copy

  Remarks

  You can also use event listeners (on) for the same purpose: the event "initialized" indicates success, and "error" indicates an error.