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React Native SDK reference


This SDK is not currently supported on Harness Self-Managed Enterprise Edition (on premises).

This topic describes how to use the Harness Feature Flags SDK for your React Native application. 

For getting started quickly, you can use our sample code from the SDK README. You can also clone and run a sample application from the React Native SDK GitHub Repository.

Before You Begin


The current version of this SDK is 1.0.2.


To use this SDK, make sure you: 

Install the SDK

To set up the React Native SDK, complete the following steps:

Install directly to the package.json file

Install the React Native SDK by adding it to your project's package.json file:

"ff-react-native-client-sdk": "1.0.2",

Install using npm

You can also use npm install:

$ npm install --save ff-react-native-client-sdk

Install on IOS

For installing on iOS, run the following commands from the project root folder:

$ cd ios  
$ pod install

Initialize the SDK

To initialize the React Native SDK, you need to:

  1. Import the cfClientInstance base instance. This provides all the features of the SDK.
  2. Add your Client SDK key to connect to your Harness Environment.
  3. Add a Target that you want to Evaluate against a Feature Flag.
  4. (Optional) Configure the SDK options.
  5. Complete the initialization with the SDK using the Client SDK Key, Target, and Configuration parameters you set.

Import the base instance

Use the following command to import the cfClientInstance base instance:

import cfClientInstance from 'ff-react-native-client-sdk';

Add your Client SDK Key

To connect to the correct Environment that you set up on the Harness Platform, you need to add the Client SDK Key from that Environment. Input the Client SDK Key into the apiKey parameter, for example:

const apiKey = "YOUR_API_KEY";

Add a Target

What is a Target?
Targets are used to control which users see which Variation of a Feature Flag, for example, if you want to do internal testing, you can enable the Flag for some users and not others. When creating a Target, you give it a name and a unique identifier. Often Targets are users but you can create a Target from anything that can be uniquely identified, such as an app or a machine.

For more information about Targets, go to Targeting Users With Flags.

To add a Target that you want to Evaluate, build it using cfTarget and pass in arguments for the following:

identifierUnique ID for the Target.Required.identifier("HT_1")
Regex requirements for Target names and identifiers


Regex: ^[A-Za-z0-9.@_-]*$
Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
_ (underscore)

The characters can be lowercase or uppercase but cannot include accented letters, for example Cafe_789.

Name Regex: ^[\\p{L}\\d .@_-]*$

Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
_ (underscore)

The characters can be lowercase or uppercase and can include accented letters, for example Café_123.

For example:

const cfTarget = new CfTarget();  
cfTarget.identifier = 'HT_1';

Configure the SDK

You can configure the following features of the SDK:

NameExampleDescriptionDefault Value
baseUrlbaseUrl = "``"``;The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000
eventUrleventUrl = "``"``;The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000
pollIntervalpollInterval = 60;The interval in seconds that we poll for changes when you are using stream mode.60 (seconds)
streamEnabledstreamEnabled = true;Set to true to enable streaming mode.Set to false to disable streaming mode.true
analyticsEnabledanalyticsEnabled = true;Set to true to enable analytics.Set to false to disable analytics.Note: When enabled, analytics data is posted every 60 seconds.true

Use cfConfiguration to declare the configuration options you want to use, for example:

const cfConfiguration = new CfConfiguration();  
cfConfiguration.streamEnabled = false;

Complete the initialization

Complete the initialization using the apiKey, cfConfiguration, and cfTarget variables, for example:

const result = await cfClientInstance.initialize(apiKey, cfConfiguration, cfTarget);

Sample of initializing the SDK

import cfClientInstance, {CfConfiguration, CfTarget} from 'ff-react-native-client-sdk';  

const client = cfClientInstance;

const cfConfiguration = new CfConfiguration();
cfConfiguration.streamEnabled = true;

const cfTarget = new CfTarget();
cfTarget.identifier = 'Harness_Target_1';

const apiKey = "YOUR_API_KEY";

const result = await cfClientInstance.initialize(apiKey, cfConfiguration, cfTarget);

Evaluate a Flag

Evaluating a Flag is when the SDK processes all Flag rules and returns the correct Variation of that Flag for the Target you provide. 

If a matching Flag can’t be found, or the SDK can’t remotely fetch flags, the default value is returned. 

There are different methods for the different Variation types and for each method you need to pass in:

  • Identifier of the Flag you want to evaluate
  • The default Variation

Evaluate a boolean Variation

//get boolean evaluation  
let evaluation = await client.boolVariation("demo_bool_evaluation", false)

Evaluate a number Variation

//get number evaluation  
let numberEvaluation = await client.numberVariation("demo_number_evaluation", 0)

Evaluate a string Variation

//get string evaluation  
let stringEvaluation = await client.stringVariation("demo_string_evaluation", "default");

Evaluate a JSON Variation

//get json evaluation  
let jsonEvaluation = await client.jsonVariation("demo_json_evaluation", {});

Listen for events

Register the event listener

Use client.registerListener to register a listener for different events that might be triggered by SDK.

The possible events and their responses are outlined in the following table:

Event TypeReturn Value

Close the event listener

When the listener is not needed, you can remove the desired listener from the internal list to avoid unexpected behavior.


Test your app is connected to Harness

When you receive a response showing the current status of your Feature Flag, go to the Harness Platform and toggle the Flag on and off. Then, check your app to verify if the Flag Variation displayed is updated with the Variation you toggled.


The SDK must run for at least 60 seconds before it sends metrics. Please ensure metrics have not been disabled in the SDK.

Close the SDK

When SDK is not needed, for example, when the app is not running, you can shut down the SDK. This can avoid potential memory leaks.


Additional options

Use the Harness Relay Proxy

When using your Feature Flag SDKs with a Harness Relay Proxy you need to change the default URL.

To do this, import the following URL helper functions:

from featureflags.config import with_base_url  
from featureflags.config import with_events_url

Then pass them with the new URLs when creating your client.

    client = CfClient(api_key,  

Use our public API methods

Our Public API exposes the following methods that you can use:

async initialize(apiKey: string, config: CfConfiguration, target:CfTarget)
boolVariation(evalutionId: string, defaultValue?: boolean)
stringVariation(evalutionId: string, defaultValue?:string)
numberVariation(evalutionId: string, defaultValue?:number)
jsonVariation(evalutionId: string, defaultValue: any)
registerListener(listener: (type: string, flags: any) => void)
unregisterListener(listener: (type: string, flags: any) => void)

Sample code for a React application

Here is a sample code for using Harness Feature Flag SDKs with a React Native application. To learn more about using the sample React application, go to the React Native SDK GitHub repository.

import cfClientInstance, {CfConfiguration, CfTarget} from '@harnessio/ff-react-native-client-sdk';  

export default function App() {
const flagName = 'harnessappdemodarkmode';

const [client, setClient] = useState(null);
const [flagValue, setFlagValue] = useState(null);

async function initializeClient() {
let cfClient = cfClientInstance;
let cfConfig = new CfConfiguration();
cfConfig.streamEnabled = true;

const cfTarget = new CfTarget();
cfTarget.identifier = 'Harness RN Sample App'

const apiKey = "your-client-sdk-key";

try {
await cfClientInstance.initialize(apiKey, cfConfig, cfTarget);
} catch (err) {

async function evalFlag() {
let res = await client.boolVariation(flagName, false);

useEffect(() => {
if (client == null) {
} else {

return (
<View style={styles.container}>
Feature flag '{flagName}' is {JSON.stringify(flagValue)}

const styles = StyleSheet.create({
container: {
flex: 1,
backgroundColor: '#fff',
alignItems: 'center',
justifyContent: 'center',