Variables

Variables are key/value pairs of data that we evaluate against features using Featurevisor SDKs in our applications.

They are one of the 3 different types of values that we can evaluate against features, including:

• Flags
• Variations
• Variables (you are here)

Visual explanation#

Default variable values#

When defining a feature, we can set a default value for each variable:

description: My feature here...
tags:
  - web
  - ios
  - android
bucketBy: userId
variablesSchema:
  my_variable:
    type: string
    defaultValue: default value
rules:
  production:
    - key: nl
      segments: netherlands
      percentage: 0
    - key: de
      segments: germany
      percentage: 80
    - key: us
      segments: usa
      percentage: 100

Whenever the variable is evaluated, if the feature itself is evaluated as enabled, the default value will be served.

Disabled variable values#

The feature itself will not always be evaulated as enabled, given it is being rolled out gradually targeting specific segments.

If we wish to serve a variable value when the feature is disabled, we can make use of the disabledValue property:

# ...
variablesSchema:
  my_variable:
    type: string
    defaultValue: default value
    disabledValue: different value for disabled feature

Overrides at rule level#

There are times when we want to override the default value for a variable for a specific rule alone. In that case, we can make use of the variables property at individual rule level:

# ...
rules:
  production:
    - key: nl
      segments: netherlands
      percentage: 0
    - key: de
      segments: germany
      percentage: 80
    - key: us
      segments: usa
      percentage: 100
      variables:
        my_variable: different value for USA

Overrides at variation level#

It's very much possible that we are running experiments, and want to override the variable value depending on the variation that the user is bucketed into.

We can achieve that by expressing the variations property as follows:

# ...
variations:
  - value: A
    weight: 50
    # default variable values will be served for this variation
    # if no `variables` property is defined here
  - value: B
    weight: 50
    variables:
      my_variable: different value for B variation
# ...

This approach basically makes it a multivariate test experiment, which you can read more about here.

Usage of SDK#

If we take JavaScript SDK as an example, variable values can be evaluated as follows:

import { createInstance } from '@featurevisor/sdk'
// create Featurevisor SDK instance
const f = createInstance({
  datafile: { ... }
});
// set some common context to evaluate values against
f.setContext({
  userId: '123',
});
const myVariableValue = f.getVariable('my_feature', 'my_variable');
const anotherVariableValue = f.getVariable('another_feature', 'another_variable');

Learn about more advanced use cases for evaluations here.