Flags

Flags are boolean (on/off) values 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 (you are here)
Variations
Variables

Visual explanation#

Flags illustration

Above we can see that:

We have 3 different users coming to our application
We have 3 different rules targeting the Netherlands, Germany, and US
Each rule having a different rollout percentage

Below we will find out how to express this requirement as a feature in Featurevisor.

Expressing the feature#

Assuming we already have the segments created for the countries, we can define our feature as follows:

features/my_feature.yml

description: My feature description here...
tags:
  - web
  - ios
  - android
bucketBy: userId
rules:
  production:
    - key: nl               # any unique string is fine here
      segments: netherlands # references segments/netherlands.yml
      percentage: 0         # 0 means disabled for all
    - key: de
      segments: germany
      percentage: 80
    - key: us
      segments: usa
      percentage: 100

Learn more in:

Features: express more complex features
Tags: generate separate datafiles (JSON files) containing only the features we need for our application(s) to load on demand
Bucketing: allows evaluating values consistently for the same user throughout the whole session across different devices (for e.g., a page refresh should not lead to evaluating a different value for the same user)
Rules: different rules different sets of segments with their own gradual rollout percentage value
Environments: for having different sets of rules per environment (like staging and production)

Mapping the evaluations#

Above rules for the feature my_feature suggest that:

Everyone in the Netherlands would see it as disabled
80% of traffic in Germany would see it as enabled (other 20% would see it as disabled consistently)
100% of traffic in USA would see it as enabled

Usage of SDK#

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

your-app/index.js

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 myFeatureIsEnabled = f.isEnabled('my_feature_name');
const anotherFeatureIsEnabled = f.isEnabled('another_feature');

Learn about more advanced use cases for evaluations here.