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Get Feature Variable

This topic describes the Get Feature Variable method which evaluates the specified feature variable of a specific variable type and returns its value.

Evaluates the specified feature variable of a specific variable type and returns its value.

This method is used to evaluate and return a feature variable. Multiple versions of this method are available and are named according to the data type they return:

This method takes into account the user attributes passed in, to determine if the user is part of the audience that qualifies for the experiment.


Starting in v3.3.0 of the SDK, you can use the generic feature variable accessor. This can return a number, boolean, or string depending on the variable's defined type.

function getFeatureVariable(featureKey, variableKey, userId, attributes)


Returns the value of the specified Boolean variable.

function getFeatureVariableBoolean(featureKey, variableKey, userId, attributes)


Returns the value of the specified double variable.

function getFeatureVariableDouble(featureKey, variableKey, userId, attributes)


Returns the value of the specified integer variable.

function getFeatureVariableInteger(featureKey, variableKey, userId, attributes)


Returns the value of the specified string variable.

function getFeatureVariableString(featureKey, variableKey, userId, attributes)


Returns the value of the specified JSON variable.

function getFeatureVariableJson(featureKey, variableKey, userId, attributes)


SDK v3.0, v3.1, v3.3


Each of the Get Feature Variable methods follows the same logic as Is Feature Enabled:

  1. Evaluate any feature tests running for a user.
  2. Check the default configuration on a rollout.

The default value is returned if neither of these are applicable for the specified user, or if the user is in a variation where the feature is disabled.



Unlike Is Feature Enabled, the Get Feature Variable methods do not trigger an impression event. This means that if you are running a feature test, events will not be counted until you call Is Feature Enabled. If you do not call Is Feature Enabled, you will not see any visitors on your results page.


Required and optional parameters are listed below.

stringThe feature key is defined from the Features dashboard; see Use feature flags.
stringThe key that identifies the feature variable. For more information, see: Create feature variables.
stringThe user ID string uniquely identifies the participant in the experiment. For more information, see: Handle user IDs.
mapA map of custom key-value string pairs specifying attributes for the user that are used for audience targeting and results segmentation. Non-string values are only supported in the 3.0 SDK and above.


@return {string | number | boolean | object | null} The value of the variable, or null if the feature key is invalid, the variable key is invalid, or there is a mismatch with the type of the variable.


var attributes = {
  device: 'iPhone',
  lifetime: 24738388,
  is_logged_in: true,

var featureVariableValue = optimizelyClient.getFeatureVariableDouble('my_feature_key', 'double_variable_key', 'user_123', attributes);

// or in v3.3+ you can use the untyped variable accessor, which will return a number if the variable you defined in the Optimizely Dashboard is of type double
var featureVariableValue = optimizelyClient.getFeatureVariable('my_feature_key', 'double_variable_key', 'user_123', attributes);

See also

Is Feature Enabled

Side effects

In SDKs v3.1 and later: Invokes the DECISION notification listener if this listener is enabled.

Source files

The language/platform source files containing the implementation for Node are available on GitHub.