title: Feature flag module

Concept

This module enables the usage of feature flags.

interface FeatureFlag<T> {
  key: string;
  title?: string;
  description?: string;
  source?: string;
  enabled?: boolean;
  readOnly?: boolean;
  value?: T;
}

Configuration

import { enableFeatureFlags } from '@equinor/fusion-framework-module-feature-flag';

import { 
  createLocalStoragePlugin,
  createUrlPlugin
} from '@equinor/fusion-framework-module-feature-flag/plugins';

export const configure: ModuleInitiator = (configurator, args) => {
  enableFeatureFlags(configurator, builder => {
    builder.addPlugin(
      /** define flags that will be stored in local storage when toggled */
      createLocalStoragePlugin([
        {
          key: MyFeatures.MyFlag,
          title: 'this is a flag',
        },
        {
          key: MyFeatures.MyUrlFlag,
          title: 'this feature can be toggled by ?my-url-flag=true',
        }
      ])
    );
    builder.addPlugin(
      /** define flags which are allowed to be toggled from url */
      createUrlPlugin([ MyFeatures.MyUrlFlag ])
    )
  });
}

[!NOTE] In the near future, features will be as an API service

Plugins

sequenceDiagram
    autonumber
    participant Configuration
    participant Module
    participant C as Configurator
    participant Plugin
    participant Provider

    Configuration->>Module: enableFeatureFlagging
    Module->>C: create configurator
    C->>Configuration: configuration builder
    Configuration->>Plugin: enablePlugin
    Plugin->>C: setup callback
    Configuration-->>+Module: initialize
    Module-->>+C: initialize
    C-->>Plugin: setup
    Plugin-->>C: plugin instance
    C->>-Module: module config
    Module->>Provider: create provider
    Provider-->>Plugin: connect
    Provider-->>Plugin: subscribe to toggle actions
    Module-->>-Configuration: Feature flag provider

1. when configuring the framework, the feature flag module is enabled
2. the module creates a configuration builder (see BaseConfigBuilder).
3. the module returns an configuration builder callback function
4. when building the configuration, plugins are enabled to control feature flags
   • the plugin can access the provider to toggle flags
   • the plugin can set/add flags, like update/create flags from a rest call after initialization
   • the plugin can subscribe to the provider state, like storing a flag to locale state.
5. the plugin return a setup callback function which is called when the module is initialize
   • the plugin receives ConfigBuilderCallbackArgs for accessing other modules
   • the plugin return a callback for generating initial flags for the provider
   • the plugin returns a callback for accessing the feature flag provider
6. the framework initializes the module
7. the module initializes configuration
8. the configuration calls the registered plugins setup function
9. Plugin instance
   • the plugin creates initial flags, like read stored flags or fetch flags from a service
   • the plugin returns a callback function for connecting the plugin to the provider
10. the configurator return an instance of the config
11. the module create a provider instance
12. the provider connects the plugins
13. the provider subscribes to toggle actions and connects plugin toggle handlers
14. the module returns the feature flag module to the framework

export interface FeatureFlagPlugin {
    /**
     * connect the plugin to the provider
     */
    connect: (args: { provider: IFeatureFlagProvider }) => VoidFunction | Subscription;

    /**
     * generate initial value for the provider
     */
    initial?: () => ObservableInput<Array<IFeatureFlag>>;
}

Local Storage

import { createLocalStoragePlugin } from '@equinor/fusion-framework-module-feature-flag/plugins';

plugin for allowing to store the toggled state of a feature flag

Url

import { createUrlPlugin } from '@equinor/fusion-framework-module-feature-flag/plugins';

plugin for toggling features threw url search params

Custom

initial

async callback function which returns the initial feature flags of the plugin

connect

async callback which allows the plugin to connect to the feature flag provider

import { 
  enableFeatureFlagging, 
  type FeatureFlagPluginConfigCallback 
} from '@equinor/fusion-framework-module-feature-flag';

const customPlugin: FeatureFlagPluginConfigCallback = async (args) => {
  const myModule = await args.requireModule('my-module');
  return {
    initial: () => fetch('/api/features')
      .then(res => res.json())
      .then(features => features.map(feature => feature.source = 'my-source')),
    connect: ({provider}) => {
      /** subscribe to changes of feature flags */
      provider.onFeatureToggle: async({flags}) => {
        await fetch(
          '/api/me/features', 
          { 
            method: 'PATCH', 
            body: flags.filter(feature => feature.source === 'my-source')
          }
        )
      }
      /** update feature flags */
      signalR.received(data => {
        provider.setFeatures(data.map(feature => feature.source = 'my-source'));
      });
    },
  }
}

// ...configuration
enableFeatureFlagging(builder => {
  builder.addPlugin(customPlugin);
})

Selectors

Filter features

Operator function for filtering out specific features

import { filterFeatures } from '@equinor/fusion-framework-module-feature-flag/selectors';
const features$ = modules.featureFlag.feature$.pipe(
  filterFeatures(x => x.enabled = true);
);

Find feature

Operator for selecting a specific feature

[!IMPORTANT] The operator will not re-emit unless value or selector changes

import { findFeature } from '@equinor/fusion-framework-module-feature-flag/selectors';
const feature$ = modules.featureFlag.feature$.pipe('my-key');

Events

onFeatureFlagToggle

Event fired before a feature is toggled

onFeatureFlagsToggled

Event fired after features are toggled (state updated)

Usage

// my-code.ts
const provider = modules.featureFlag;
const fooEnabled = provider.getFeatures('foo').enabled;
console.log('feature foo is ', fooEnabled ? 'enabled' : 'disabled');