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Readme

Before you Begin

Harness Feature Flags (FF) is a feature management solution that enables users to change the software’s functionality, without deploying new code. FF uses feature flags to hide code or behaviours without having to ship new versions of the software. A feature flag is like a powerful if statement.

For more information, see https://harness.io/products/feature-flags/

To sign up, https://app.harness.io/auth/#/signup/

Harness Feature Flags Client SDK for JavaScript

Library for integrating Harness Feature Flags into JavaScript UI applications.

Install

npm i @harnessio/ff-javascript-client-sdk

yarn add @harnessio/ff-javascript-client-sdk

Usage

import { initialize, Event } from '@harnessio/ff-javascript-client-sdk'

Initialize SDK with api key and target information.

initialize(FeatureFlagSDKKey: string, target: Target, options?: Options)

In which Target and Options are defined as:

interface Target {
  identifier: string
  name?: string
  anonymous?: boolean
  attributes?: object
}

interface Options {
  baseUrl?: string
  eventUrl?: string
  eventsSyncInterval?: number
  streamEnabled?: boolean
  allAttributesPrivate?: boolean
  privateAttributeNames?: string[]
  debug?: boolean
}

For example:

const client = initialize('00000000-1111-2222-3333-444444444444', {
  identifier: YOUR_TARGET_IDENTIFIER,      // Target identifier
  name: YOUR_TARGET_NAME,                  // Optional target name
  attributes: {                            // Optional target attributes
    email: 'sample@sample.com'
  }
})

Listening to events from the `client` instance.

client.on(Event.READY, flags => {
  // Event happens when connection to server is established
  // flags contains all evaluations against SDK key
})

client.on(Event.FLAGS_LOADED, evaluations => {
  // Event happens when flags are loaded from the server
})

client.on(Event.CACHE_LOADED, evaluations => {
  // Event happens when flags are loaded from the cache
})

client.on(Event.CHANGED, flagInfo => {
  // Event happens when a changed event is pushed
  // flagInfo contains information about the updated feature flag
})

client.on(Event.DISCONNECTED, () => {
  // Event happens when connection is disconnected
})

client.on(Event.ERROR, error => {
  // Event happens when connection some error has occurred
})

client.on(Event.ERROR_AUTH, error => {
  // Event happens when unable to authenticate
})

client.on(Event.ERROR_FETCH_FLAGS, error => {
  // Event happens when unable to fetch flags from the service
})

client.on(Event.ERROR_FETCH_FLAG, error => {
  // Event happens when unable to fetch an individual flag from the service
})

client.on(Event.ERROR_METRICS, error => {
  // Event happens when unable to report metrics back to the service
})

client.on(Event.ERROR_STREAM, error => {
  // Event happens when the stream returns an error
})

Getting value for a particular feature flag

const value = client.variation('Dark_Theme', false) // second argument is default value when variation does not exist

Cleaning up

Remove a listener of an event by client.off.

client.off(Event.ERROR, error => {
  // Do something when an error occurs
})

Remove all listeners:

client.off()

On closing your application, call client.close() to close the event stream.

client.close()

Caching

In practice flags rarely change and so it can be useful to cache the last received evaluations from the server to allow your application to get started as fast as possible. Setting the cache option as true will allow the SDK to store its evaluations to localStorage and retrieve at startup. This lets the SDK get started near instantly and begin serving flags, while it carries on authenticating and fetching up-to-date evaluations from the server behind the scenes.

const client = initialize('00000000-1111-2222-3333-444444444444', {
    identifier: YOUR_TARGET_IDENTIFIER,
    name: YOUR_TARGET_NAME
  }, {
    cache: true // enable caching
  }
)

Set evaluations

In some cases it might be worthwhile providing the SDK with a set of evaluations which it can then serve instantly. You might want to consider this when you need to:

reduce application startup time by providing default values or a snapshot of evaluations. For example, if your application is server-side generated, then it might make sense to retrieve evaluations on the server and provide them in the HTML of the page to be injected into the SDK
provide network redundancy by allowing your app to detect network connectivity issues accessing the service and loading evaluations from another source

To achieve this you can call the setEvaluations method at any time after initializing the client. The setEvaluations method takes an array of Evaluation objects as an argument.

client.setEvaluations(evals);

In which Evaluation is defined as:

export interface Evaluation {
  flag: string // Feature flag identifier
  identifier: string // variation identifier
  value: boolean | string | number | object | undefined // variation value
  kind: string // boolean | json | string | int
  deleted?: boolean // mark that feature flag is deleted
}

Import directly from unpkg

In case you want to import this library directly (without having to use npm or yarn):

<script type="module">
  import { initialize, Event } from 'https://unpkg.com/@harnessio/ff-javascript-client-sdk/dist/sdk.client.js'
</script>

If you need to support old browsers which don't support ES Module:

<script src="https://unpkg.com/@harnessio/ff-javascript-client-sdk/dist/sdk.client.js"></script>
<script>
  var initialize = HarnessFFSDK.initialize
  var Event = HarnessFFSDK.Event
</script>

License

Apache version 2.

@harnessio/ff-javascript-client-sdk