Feature Flag Determination


Feature flags are only available for SDK version 2.0.0 or higher.

When using feature flags, please apply SDK version 2.0.0 or higher when adding dependencies.

A feature flag has an on and off state. You will set different functions according to each state.

Once a feature flag is applied, a specific user from your traffic should be able to either receive an off or on status. This on/off status determination can be done through the Hackle SDK.


You can pass a feature key to the isFeatureOn() method to receive status results for the user. After receiving the status, we can then implement the logic according to each status.

In the example code below, we are passing feature key 42.

// Execution should occur after the SDK is ready. Don't forget to wrap with onReady.
hackleClient.onReady(function() {
  // Determines the status of the feature flag to assign the user in a feature flag with a feature key of 42.
  // For undetermined cases, users are assigned to false (off status). 
  const isOn = hackleClient.isFeatureOn(42);

  // Logic by state
  if (isOn) {
    // Logic for on status
  } else {
    // Logic for off status


The featureDetail() method works the same as the isFeatureOn() method and additionally provides a reason for determining the status of a particular user. This can be useful when you want to check whether the manual allocation is working well or when you think that the traffic allocation you have set is not being reflected in your results.

You must pass a function key as a parameter. For the example code below, we are passing function key 42.

hackleClient.onReady(function() {
  // Status determination details
  const decision = hackleClient.featureFlagDetail(experimentKey);
  // Feature flag on/off results 
  const featureOn = decision.isOn;
  // Reason for status determination
  const reason = decision.reason;

Please refer to the table below for the full list of reasons for the different types of status distributions.

ReasonDescriptionFeature Status
SDK_NOT_READYThe SDK is not ready to use.
(e.g. trying to initialize with the wrong SDK key)
Default status(off)
FEATURE_FLAG_NOT_FOUNDNo feature flags were found for the function key you passed in.
The feature key may be incorrect or the corresponding feature flag may be in an archived state.
Default status(off)
FEATURE_FLAG_INACTIVEThe feature flag is off.Default status(off)
INDIVIDUAL_TARGET_MATCHUser has been matched to individual targeting settings.Set to individual targeting
TARGET_RULE_MATCHUser has been matched to audience targeting settings.Set to audience targeting
DEFAULT_RULEUser has not been matched to either individual targeting or audience targeting.Default status (off)
INVALID_INPUTThe input value is not valid.
(Example: Character type entered in a parameter that requires a numeric type)
Default status (off)
EXCEPTIONAn unknown error has occurred.Default status(off)

Feature Flag Parameter

  • Call featureFlagDetail() method to obtain parameter values which contains the feature flag status information
  • FeatureFlagDecisioninstance passed through the featureFlagDetail() method has full parameter setting information.
  • Parameter values you've set on the dashboard exists in the form of key and value, therefore you can use the method below to set the parameter values.
  • You can change feature flag's parameter values flexibly on the Feature Flag > Parameter Settings.
hackleClient.onReady(function() {
  const decision = hackleClient.featureFlagDetail(experimentKey);
  const parameterValue = decision.get(parameterKey, defaultValue)

  const config = decision.config
  const configParameterValue = config.get(parameterKey, defaultValue)

  // Example of string type parameter value
  const strValue = decision.get("parmeterKey", "defaultValue")
  const strValueInConfig = config.get("parmeterKey", "defaultValue")