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ReactJS

This is a thin wrapper on top of the Javascript Library, so you might want to view those docs first to familiarize yourself with the basic classes and methods.

This SDK supports both ReactJS and ReactNative environments.

Important: Starting in version 1.0.0, you must always pass a GrowthBook instance into the GrowthBookProvider. In previous versions, you were allowed to pass null as well.

Installation

Install with a package manager

npm install --save @growthbook/growthbook-react

Quick Usage

Step 1: Configure your app

import { useEffect } from "react";
import { GrowthBook, GrowthBookProvider } from "@growthbook/growthbook-react";

// Create a GrowthBook instance
const gb = new GrowthBook({
apiHost: "https://cdn.growthbook.io",
clientKey: "sdk-abc123",
enableDevMode: true,
// Only required for A/B testing
// Called every time a user is put into an experiment
trackingCallback: (experiment, result) => {
console.log("Experiment Viewed", {
experimentId: experiment.key,
variationId: result.key,
});
},
});
gb.init({
// Optional, enable streaming updates
streaming: true
})

export default function App() {
useEffect(() => {
// Set user attributes for targeting (from cookie, auth system, etc.)
gb.setAttributes({
id: user.id,
company: user.company,
});
}, [user])

return (
<GrowthBookProvider growthbook={gb}>
<OtherComponent />
</GrowthBookProvider>
);
}

Step 2: Start feature flagging!

There are a few ways to use feature flags in GrowthBook:

Feature Hooks

import { useFeatureValue, useFeatureIsOn } from "@growthbook/growthbook-react";

export default function OtherComponent() {
// Boolean on/off features
const newLogin = useFeatureIsOn("new-login-form");

// String/Number/JSON features with a fallback value
const buttonColor = useFeatureValue("login-button-color", "blue");

if (newLogin) {
return <NewLogin color={buttonColor} />;
} else {
return <Login color={buttonColor} />;
}
}

Feature Wrapper Components

import { IfFeatureEnabled, FeatureString } from "@growthbook/growthbook-react";

export default function OtherComponent() {
return (
<div>
<h1>
<FeatureString feature="site-h1" default="My Site"/>
</h1>
<IfFeatureEnabled feature="welcome-message">
<p>Welcome to our site!</p>
</IfFeatureEnabled>
</div>
);
}

useGrowthBook hook

If you need low-level access to the GrowthBook instance for any reason, you can use the useGrowthBook hook.

One example is updating targeting attributes when a user logs in:

import { useGrowthBook } from "@growthbook/growthbook-react";

export default function Auth() {
const growthbook = useGrowthBook();

const user = useUser();
useEffect(() => {
if (!user) return;
growthbook.setAttributes({
loggedIn: true,
id: user.id,
company: user.company,
isPro: user.plan === "pro"
})
}, [user, growthbook])

...
}

Loading Features

In order for the GrowthBook SDK to work, it needs to have feature definitions from the GrowthBook API. There are 2 ways to get this data into the SDK.

Built-in Fetching and Caching

If you pass an apiHost and clientKey into the GrowthBook constructor, it will handle the network requests, caching, retry logic, etc. for you automatically. If your feature payload is encrypted, you can also pass in a decryptionKey.

const gb = new GrowthBook({
apiHost: "https://cdn.growthbook.io",
clientKey: "sdk-abc123",
// Only required if you have feature encryption enabled in GrowthBook
decryptionKey: "key_abc123",
});

await gb.init({
// If the network request takes longer than this (in milliseconds), continue
// Default: `0` (no timeout)
timeout: 2000,
})

Until features are loaded, all features will evaluate to null. If you're ok with a potential flicker in your application (features going from null to their real value), you can call init without awaiting the result.

If you want to refresh the features at any time (e.g. when a navigation event occurs), you can call gb.refreshFeatures().

Error Handling

In the case of network issues, the init call will not throw an error. Instead, it will stay in the default state where every feature evaluates to null.

You can still get access to the error if needed:

const res = await gb.init({
timeout: 1000
});
console.log(res);

The return value has 3 properties:

  • status - true if the GrowthBook instance was populated with features/experiments. Otherwise false
  • source - Where this result came from. One of the following values: network, cache, init, error, or timeout
  • error - If status is false, this will contain an Error object with more details about the error

Custom Integration

If you prefer to handle the network and caching logic yourself, you can pass in a full JSON "payload" directly into the SDK. For example, you might store features in Postgres and send it down to your front-end as part of your app's initial bootstrap API call.

await gb.init({
payload: {
features: {
"feature-1": {...},
"feature-2": {...},
"another-feature": {...},
}
}
})

The data structure for "payload" is exactly the same as what is returned by the GrowthBook SDK endpoints and webhooks.

You can update the payload at any time by calling setPayload(newPayloadJSON) and there are also getPayload() and getDecryptedPayload() methods, which are useful in hybrid apps where you want to hydrate the client with data from the server.

Note: you don't need to specify clientKey or apiHost on your GrowthBook instance unless you want to enable streaming (see below) or call refreshFeatures() later.

Synchronous Init

There is a alternate synchronous version of init named initSync, which can be especially useful in SSR to prevent hydration mismatches. There are some restrictions/differences:

  • You MUST pass in payload
  • The payload MUST NOT have encrypted features or experiments
  • If you use sticky bucketing, you MUST pass stickyBucketAssignmentDocs into your GrowthBook constructor
  • The return value is the GrowthBook instance to enable easy method chaining

Waiting for Features to Load

There is a helper component <FeaturesReady> that lets you render a fallback component until features are done loading. This works for both built-in fetching and custom integrations.

<FeaturesReady timeout={500} fallback={<LoadingSpinner/>}>
<ComponentThatUsesFeatures/>
</FeaturesReady>
  • timeout is the max time you want to wait for features to load (in ms). The default is 0 (no timeout).
  • fallback is the component you want to display before features are loaded. The default is null.

If you want more control, you can use the useGrowthBook() hook and the ready flag:

const gb = useGrowthBook();

if (gb.ready) {
// Do something
}

Streaming Updates

The GrowthBook SDK supports streaming with Server-Sent Events (SSE). When enabled, changes to features within GrowthBook will be streamed to the SDK in realtime as they are published. This is only supported on GrowthBook Cloud or if running a GrowthBook Proxy Server.

Streaming in Browser Environments

SSE is supported on all major browsers, so enabling streaming is as easy as passing streaming: true into your init call:

gb.init({
streaming: true,
// Other settings...
})

You may also differentiate your streaming host URL from your API host by setting the streamingHost property in the GrowthBook constructor (ex: Remote Evaluation is done on a CDN edge worker while Streaming is done through a GrowthBook Proxy server).

Streaming on the Server

Node.js does not natively support SSE, but there is a small library you can install:

npm install --save eventsource

Instead of enabling streaming separately for every GrowthBook instance, we recommend opening a single shared stream at app startup instead:

const { setPolyfills, prefetchPayload } = require("@growthbook/growthbook");

// Configure GrowthBook to use the eventsource library
setPolyfills({
EventSource: require("eventsource"),
});

// Start a streaming connection
prefetchPayload({
apiHost: "https://cdn.growthbook.io",
clientKey: "sdk-abc123",
streaming: true
}).then(() => console.log("Streaming connection open!"))

This will work as long as you use the exact same apiHost and clientKey when creating GrowthBook instances in your middleware.

Streaming in ReactNative

Similar to Node.js, you need to install a polyfill for SSE to use streaming in a ReactNative application:

npm install --save eventsource

The, tell GrowthBook to use this polyfill:

const { setPolyfills } = require("@growthbook/growthbook");

// Configure GrowthBook to use the eventsource library
setPolyfills({
EventSource: require("eventsource"),
});

And finally, you can simply pass streaming: true into your init calls:

gb.init({
streaming: true,
// Other options...
})

Remote Evaluation

When used in a front-end context, the React SDK may be run in Remote Evaluation mode. This mode brings the security benefits of a backend SDK to the front end by evaluating feature flags exclusively on a private server. Using Remote Evaluation ensures that any sensitive information within targeting rules or unused feature variations are never seen by the client. Note that Remote Evaluation should not be used in a backend context (Hybrid SSR/CSR is also not supported).

You must enable Remote Evaluation in your SDK Connection settings. Cloud customers are also required to self-host a GrowthBook Proxy Server or custom remote evaluation backend.

To use Remote Evaluation, add the remoteEval: true property to your SDK instance. A new evaluation API call will be made any time a user attribute or other dependency changes. You may optionally limit these API calls to specific attribute changes by setting the cacheKeyAttributes property (an array of attribute names that, when changed, trigger a new evaluation call).

const gb = new GrowthBook({
apiHost: "https://gb-proxy.mydomain.io/",
clientKey: "sdk-abc123",
// Enable remote evaluation
remoteEval: true,

// Optional: only trigger a new evaluation call when the `id` and `email` attribute changes
cacheKeyAttributes: ["id", "email"],
});
note

If you would like to implement Sticky Bucketing while using Remote Evaluation, you must configure your remote evaluation backend to support Sticky Bucketing. In the case of the GrowthBook Proxy Server, this means implementing a Redis database for sticky bucketing use. You will not need to provide a StickyBucketService instance to the client side SDK.

Caching

The JavaScript SDK has 2 caching layers:

  1. In-memory cache (available on all platforms)
  2. Persistent localStorage cache (only available in browsers by default)

There are a number of cache settings you can configure within GrowthBook. This must be done BEFORE creating a GrowthBook instance.

Below are all of the default values. You can call configureCache with a subset of these fields and the rest will keep their default values.

import { configureCache } from "@growthbook/growthbook";

configureCache({
// The localStorage key the cache will be stored under
cacheKey: "gbFeaturesCache",
// Consider features stale after this much time (60 seconds default)
staleTTL: 1000 * 60,
// Cached features older than this will be ignored (24 hours default)
maxAge: 1000 * 60 * 60 * 24,
// For Remote Eval only - limit the number of cache entries (~1 entry per user)
maxEntries: 10,
// When `false`, we add a `visibilitychange` listener to disable SSE when the page is idle
disableIdleStreams: false,
// Consider a page "idle" when it is hidden for this long (default 20 seconds)
idleStreamInterval: 20000,
// Set to `true` to completely disable both in-memory and persistent caching
disableCache: false,
})

Polyfilling localStorage

Outside of a browser environment, you can still use persistent caching. You just need to provide an implementation of the localStorage interface.

Here's an example of using Redis in Node.js:

const { setPolyfills } = require("@growthbook/growthbook");

setPolyfills({
localStorage: {
// Example using Redis
getItem: (key) => redisClient.get(key),
setItem: (key, value) => redisClient.set(key, value),
}
});

This must be done BEFORE you call either prefetchPayload or create the first GrowthBook instance.

Experimentation (A/B Testing)

In order to run A/B tests, you need to set up a tracking callback function. This is called every time a user is put into an experiment and can be used to track the exposure event in your analytics system (Segment, Mixpanel, GA, etc.).

const gb = new GrowthBook({
apiHost: "https://cdn.growthbook.io",
clientKey: "sdk-abc123",
trackingCallback: (experiment, result) => {
// Example using Segment
analytics.track("Experiment Viewed", {
experimentId: experiment.key,
variationId: result.key,
});
},
});

This same tracking callback is used for both feature flag experiments and Visual Editor experiments.

Feature Flag Experiments

There is nothing special you have to do for feature flag experiments. Just evaluate the feature flag like you would normally do. If the user is put into an experiment as part of the feature flag, it will call the trackingCallback automatically in the background.

// If this has an active experiment and the user is included,
// it will call trackingCallback automatically
useFeatureIsOn("new-signup-form")

If the experiment came from a feature rule, result.featureId in the trackingCallback will contain the feature id, which may be useful for tracking/logging purposes.

Visual Editor Experiments

Experiments created through the GrowthBook Visual Editor will run automatically as soon as their targeting conditions are met.

Note: Visual Editor experiments are only supported in a web browser environment. They will not run in React Native or during Server Side Rendering (SSR).

If you are using this SDK in a Single Page App (SPA), you will need to let the GrowthBook instance know when the URL changes so the active experiments can update accordingly.

For example, in Next.js, you could do this:

function updateGrowthBookURL() {
gb.setURL(window.location.href);
}

export default function MyApp() {
// Subscribe to route change events and update GrowthBook
const router = useRouter();
useEffect(() => {
router.events.on("routeChangeComplete", updateGrowthBookURL);
return () => router.events.off("routeChangeComplete", updateGrowthBookURL);
}, []);

// ...
}

URL Redirect Experiments

Similarly to Visual Editor experiments, URL redirect tests will run automatically if targetting conditions are met.

If you are using this SDK in a Single Page App (SPA), you'll want to pass in a custom navigation function into the SDK (as default navigation for URL Redirects uses window.location.replace(url)) and set the navigateDelay to 0.

// Example in Next.js
import router from "next/router";

const gb = new GrowthBook({
navigate: (url) => router.replace(url),
navigateDelay: 0,
// ... other settings
});

For SPA's you will also need to let the GrowthBook instance know when the URL changes so the active experiments can update accordingly.

// Call this every time a navigation event happens in your SPA
function onRouteChange() {
gb.setURL(window.location.href);
}

Sticky Bucketing

Sticky bucketing ensures that users see the same experiment variant, even when user session, user login status, or experiment parameters change. See the Sticky Bucketing docs for more information. If your organization and experiment supports sticky bucketing, you must implement an instance of the StickyBucketService to use Sticky Bucketing. The JS SDK exports several implementations of this service for common use cases, or you may build your own:

  • LocalStorageStickyBucketService — For simple bucket persistence using the browser's LocalStorage (can be polyfilled for other environments).

  • BrowserCookieStickyBucketService — For simple bucket persistence using browser cookies, which are transportable to the back end. Assumes js-cookie is implemented (can be polyfilled). Cookie attributes can also be configured.

  • ExpressCookieStickyBucketService — For NodeJS/Express controller-level bucket persistence using browser cookies; intended to be interoperable with BrowserCookieStickyBucketService. Assumes cookie-parser is implemented (can be polyfilled). Cookie attributes can also be configured.

  • RedisStickyBucketService — For NodeJS Redis-based bucket persistence. Requires an ioredis Redis client instance to be passed in.

  • Build your own — Implement the abstract StickyBucketService class and connect to your own data store, or custom wrap multiple service implementations (ex: read/write to both cookies and Redis).

Implementing most StickyBucketService implementations is straightforward and works with minimal setup. For instance, to use the BrowserCookieStickyBucketService:

import { BrowserCookieStickyBucketService } from "@growthbook/growthbook";
import Cookies from 'js-cookie';

const gb = new GrowthBook({
apiHost: "https://cdn.growthbook.io",
clientKey: "sdk-abc123",
stickyBucketService: new BrowserCookieStickyBucketService({
jsCookie: Cookies,
}),
// ...
});

Next.js

If you are using Next.js, checkout our example apps for Next with App Router and Next with Pages Router.

The examples above show how to use GrowthBook with a number of different rendering strategies and app setups and the App Router example has been updated to support the latest features in Next 14.

Server Side Rendering (SSR)

This SDK fully supports server side rendering with React.

React Server Components

If your framework supports the new React Server Components (RSC), welcome to the future! GrowthBook works great with modern React.

First, if you are running experiments with GrowthBook, you will need to fire analytics tracking calls to record which variation a user is assigned. Analytics tools are often only supported client-side, so you can create a small Client Component first:

"use client";
import { TrackingData } from "@growthbook/growthbook-react";

// Helper component to track experiment views from server components
export default function GrowthBookTracking({ data }: { data: TrackingData[] }) {
useEffect(() => {
data.forEach(({ experiment, result }) => {
console.log("Viewed Experiment", {
experimentId: experiment.key,
variationId: result.key
});
});
}, [data])

return null;
}

The React SDK relies on client-side Context, so for Server Components, you need to import our Javascript SDK @growthbook/growthbook instead.

import { GrowthBook } from "@growthbook/growthbook";
import GrowthBookTracking from "./GrowthBookTracking";

export default async function MyServerPage() {
// Create and initialize a GrowthBook instance
const gb = new GrowthBook({
apiHost: process.env.NEXT_PUBLIC_GROWTHBOOK_API_HOST,
clientKey: process.env.NEXT_PUBLIC_GROWTHBOOK_CLIENT_KEY,
decryptionKey: process.env.NEXT_PUBLIC_GROWTHBOOK_DECRYPTION_KEY,
});
await gb.init({ timeout: 1000 });

// Set targeting attributes for the user/page
await gb.setAttributes({
// TODO: get this from cookies, headers, etc.
id: cookies().get("my_uuid")?.value || "",
});

// Evaluate any feature flags
const showBanner = gb.isOn("showBanner");
const title = gb.getFeatureValue("title", "My Site");

// If the above features ran any experiments, get the tracking call data
// This is passed into the <GrowthBookTracking> client component below
const trackingData = gb.getDeferredTrackingCalls();

// Cleanup
gb.destroy();

return (
<div>
<h1>{title}</h1>
{showBanner && (
<div className="sale">There's a Sale!</div>
)}

<GrowthBookTracking data={trackingData} />
</div>
);
}

Hydrating Client Components From the Server

The best part about React Server Components, is that you can easily share feature definitions with your Client Components. By doing this, you avoid any network requests from the browser and any flickering that goes along with that.

Let's first create a GrowthBookWrapper wrapper that takes a payload prop and uses it to initialize a GrowthBook instance:

"use client";
import {
GrowthBook,
GrowthBookProvider,
GrowthBookPayload
} from "@growthbook/growthbook-react";
import { PropsWithChildren, useMemo } from "react";
import Cookies from "js-cookie";

export default function GrowthBookWrapper({
payload,
children,
}: PropsWithChildren<{ payload: GrowthBookPayload }>) {
// Create a singleton GrowthBook instance for this page
const gb = useMemo(
() =>
new GrowthBook({
apiHost: process.env.NEXT_PUBLIC_GROWTHBOOK_API_HOST,
clientKey: process.env.NEXT_PUBLIC_GROWTHBOOK_CLIENT_KEY,
decryptionKey: process.env.NEXT_PUBLIC_GROWTHBOOK_DECRYPTION_KEY,
trackingCallback: (experiment, result) => {
console.log("Viewed Experiment", {
experimentId: experiment.key,
variationId: result.key
});
},
// Targeting attributes
attributes: {
id: Cookies.get("my_uuid"),
},
}).initSync({
payload,
// Optional, enable streaming updates
streaming: true,
}),
[payload]
);

return <GrowthBookProvider growthbook={gb}>{children}</GrowthBookProvider>;
}

Now we'll make a really simple client component using the GrowthBook React SDK:

"use client";
import { useFeatureIsOn } from "@growthbook/growthbook-react";

export default function OtherComponent() {
const clientFeature = useFeatureIsOn("client-feature");
return (
<p>Client feature: {clientFeature ? "ON" : "OFF"}</p>
)
}

Now, we can render these from our server component:

import { GrowthBook } from "@growthbook/growthbook";
import GrowthBookWrapper from "./GrowthBookWrapper";
import OtherComponent from "./OtherComponent";
import GrowthBookTracking from "./GrowthBookTracking";

export default async function MyServerPage() {
// Create and initialize a GrowthBook instance
const gb = new GrowthBook({
apiHost: process.env.NEXT_PUBLIC_GROWTHBOOK_API_HOST,
clientKey: process.env.NEXT_PUBLIC_GROWTHBOOK_CLIENT_KEY,
decryptionKey: process.env.NEXT_PUBLIC_GROWTHBOOK_DECRYPTION_KEY,
});
await gb.init({ timeout: 1000 });

// Set targeting attributes for the user
gb.setAttributes({
id: cookies().get("my_uuid")?.value || "",
});

// Evaluate any feature flags
const serverFeature = gb.isOn("server-feature");

// If the above features ran any experiments, get the tracking call data
// This is passed into the <GrowthBookTracking> client component below
const trackingData = gb.getDeferredTrackingCalls();

// Get the payload to hydrate the client-side GrowthBook instance
// We need the decrypted payload so the initial client-render can be synchronous
const payload = gb.getDecryptedPayload();

// Cleanup your GrowthBook instance
gb.destroy();

return (
<div>
<p>Server feature: {serverFeature ? "ON" : "OFF"}</p>
<GrowthBookWrapper payload={payload}>
<OtherComponent>
</GrowthBookWrapper>
<GrowthBookTracking data={trackingData} />
</div>
);
}

Traditional SSR

Before React Server Components, each framework implemented their own way to do data fetching and SSR. This example uses Next.js getServerSideProps method, but other frameworks should be similar.

With this approach, feature flags are evaluated once when the page is rendered. If a feature flag changes, the user would need to refresh the page to see it.

export const getServerSideProps = async (context) => {
// Create and initialize a GrowthBook instance
const gb = new GrowthBook({
apiHost: process.env.GROWTHBOOK_API_HOST,
clientKey: process.env.GROWTHBOOK_CLIENT_KEY,
decryptionKey: process.env.GROWTHBOOK_DECRYPTION_KEY,
});
await gb.init({ timeout: 1000 });

// Set targeting attributes for the user
await gb.setAttributes({
id: context?.cookies?.my_uuid || "",
});

// Evaluate any feature flags
const showBanner = gb.isOn("show-banner");
const title = gb.getFeatureValue("title", "My Site");

// If the above features ran any experiments, get the tracking call data
// This is passed into the <GrowthBookTracking> client component below
const trackingData = gb.getDeferredTrackingCalls();

// Cleanup
gb.destroy();

// Pass the result into your component
return {
props: {
showBanner,
title,
trackingData
}
}
}

export default function MyPage({ title, showBanner, trackingData }) {
useEffect(() => {
trackingData?.forEach(({experiment, result}) => {
// TODO: Track in your analytics tool
console.log("Viewed Experiment", {
experimentId: experiment.key,
variationId: result.key
});
});
}, [trackingData])

return (
<div>
<h1>{title}</h1>
{showBanner && (
<div className="sale">There's a Sale!</div>
)}
</div>
)
}

Hybrid (SSR + Client-side)

Instead of passing the result of individual feature flags to your component, you can also pass the entire payload. By doing this, you get the benefits of client-side rendering (interactivity, realtime feature flag updates) plus the benefits of SSR (no flickering, improved SEO).

export const getServerSideProps = async (context) => {
// Create and initialize a GrowthBook instance
const gb = new GrowthBook({
apiHost: process.env.NEXT_PUBLIC_GROWTHBOOK_API_HOST,
clientKey: process.env.NEXT_PUBLIC_GROWTHBOOK_CLIENT_KEY,
decryptionKey: process.env.NEXT_PUBLIC_GROWTHBOOK_DECRYPTION_KEY,
});
await gb.init({ timeout: 1000 });

// Get the payload to hydrate the client-side GrowthBook instance
// We need the decrypted payload so the initial client-render can be synchronous
const payload = gb.getDecryptedPayload();

// Cleanup
gb.destroy();

// Pass the result into your component
return {
props: {
payload
}
}
}

export default function MyPage({ payload }) {
// Create a singleton GrowthBook instance for this page
const gb = useMemo(
() =>
new GrowthBook({
apiHost: process.env.NEXT_PUBLIC_GROWTHBOOK_API_HOST,
clientKey: process.env.NEXT_PUBLIC_GROWTHBOOK_CLIENT_KEY,
decryptionKey: process.env.NEXT_PUBLIC_GROWTHBOOK_DECRYPTION_KEY,
trackingCallback: (experiment, result) => {
console.log("Viewed Experiment", {
experimentId: experiment.key,
variationId: result.key
});
},
attributes: {
id: Cookies.get("my_uuid"),
},
}).initSync({
payload,
// Optional, enable streaming updates
streaming: true,
}),
[payload]
);

return <GrowthBookProvider growthbook={gb}><MyComponent></GrowthBookProvider>;
}

Then, within MyComponent, you can use any of the normal client-side hooks or helper components - useFeatureIsOn, useFeatureValue, etc.

API Reference

There are a number of configuration options and settings that control how GrowthBook behaves.

Attributes

You can specify attributes about the current user and request. These are used for two things:

  1. Feature targeting (e.g. paid users get one value, free users get another)
  2. Assigning persistent variations in A/B tests (e.g. user id "123" always gets variation B)

The following are some commonly used attributes, but use whatever makes sense for your application.

new GrowthBook({
attributes: {
id: "123",
loggedIn: true,
deviceId: "abc123def456",
company: "acme",
paid: false,
url: "/pricing",
browser: "chrome",
mobile: false,
country: "US",
},
});

Updating Attributes

If attributes change, you can call setAttributes() to update. This will completely overwrite any existing attributes. To do a partial update, use the following pattern:

gb.setAttributes({
// Only update the `url` attribute, keep the rest the same
...gb.getAttributes(),
url: "/new-page"
})

Secure Attributes

When secure attribute hashing is enabled, all targeting conditions in the SDK payload referencing attributes with datatype secureString or secureString[] will be anonymized via SHA-256 hashing. This allows you to safely target users based on sensitive attributes. You must enable this feature in your SDK Connection for it to take effect.

If your SDK Connection has secure attribute hashing enabled, you will need to manually hash any secureString or secureString[] attributes that you pass into the GrowthBook SDK.

To hash an attribute, use a cryptographic library with SHA-256 support, and compute the SHA-256 hashed value of your attribute plus your organization's secure attribute salt.

const salt = "f09jq3fij"; // Your organization's secure attribute salt (see Organization Settings)

// hashing a secureString attribute
const userEmail = sha256(salt + user.email);

// hashing an secureString[] attribute
const userTags = user.tags.map(tag => sha256(salt + tag));

gb.setAttributes({
id: user.id,
loggedIn: true,
email: userEmail,
tags: userTags,
});

await gb.init();

// In this example, we are using Node.js's built-in crypto library
function sha256(str) {
return crypto.createHash("sha256").update(str).digest("hex");
}

Note that in a browser context, we will not be able to natively access the Node.js crypto library. In modern browsers window.crypto.subtle is available, although calls are asynchronous. You would need to await all attribute hashing to complete before calling gb.setAttributes().

async function sha256(str) {
const buffer = await crypto.subtle.digest("SHA-256", new TextEncoder().encode(str));
const hashArray = Array.from(new Uint8Array(buffer));
return hashArray.map(byte => byte.toString(16).padStart(2, "0")).join("");
}

Alternatively, CryptoJS (https://www.npmjs.com/package/crypto-js) provides a synchronous API:

import sha256 from 'crypto-js/sha256';

const userEmail = sha256(salt + user.email);

Feature Usage Callback

GrowthBook can fire a callback whenever a feature is evaluated for a user. This can be useful to update 3rd party tools like NewRelic or DataDog.

new GrowthBook({
onFeatureUsage: (featureKey, result) => {
console.log("feature", featureKey, "has value", result.value);
},
});

Note: If you evaluate the same feature multiple times (and the value doesn't change), the callback will only be fired the first time.

Dev Mode

There is a GrowthBook Chrome DevTools Extension that can help you debug and test your feature flags in development.

In order for this to work, you must explicitly enable dev mode when creating your GrowthBook instance:

const gb = new GrowthBook({
enableDevMode: true,
});

To avoid exposing all of your internal feature flags and experiments to users, we recommend setting this to false in production in most cases.

Inline Experiments

Depending on how you configure feature flags, they may run A/B tests behind the scenes to determine which value gets assigned to the user.

Sometimes though, you want to run an inline experiment without going through a feature flag first. For this, you can use either the useExperiment hook or the Higher Order Component withRunExperiment:

View the Javascript SDK Docs for all of the options available for inline experiments

useExperiment hook

import { useExperiment } from "@growthbook/growthbook-react";

export default function OtherComponent() {
const { value } = useExperiment({
key: "new-headline",
variations: ["Hello", "Hi", "Good Day"]
});

return <h1>{value}</h1>;
}

withRunExperiment (class components)

Note: This library uses hooks internally, so still requires React 16.8 or above.

import { withRunExperiment } from "@growthbook/growthbook-react";

class OtherComponent extends React.Component {
render() {
// The `runExperiment` prop is identical to the `useExperiment` hook
const { value } = this.props.runExperiment({
key: "headline-test",
variations: ["Hello World", "Hola Mundo"]
});
return <h1>{value}</h1>;
}
}
// Wrap your component in `withRunExperiment`
export default withRunExperiment(OtherComponent);

TypeScript support

Some hooks are available in type-safe versions. These require you to pass in your generated types as the generic argument.

See the GrowthBook CLI documentation for more information on generating type definitions and JavaScript TypeScript Scrict Typing for how to use them.

useGrowthBook<T>()

A type-safe version of the useGrowthBook() hook is available. Everywhere you use useGrowthBook(), pass the generated features as the generic argument:

const growthbook = useGrowthBook<AppFeatures>()

In that case, the hook will return GrowthBook<AppFeatures> | undefined.

You can reduce this boilerplate by creating your own hook, e.g.:

// ./src/utils/growthbook.ts
import { useGrowthBook as _useGrowthBook } from "@growthbook/growthbook-react";

export const useGrowthBook = (): GrowthBook<AppFeatures> | undefined =>
_useGrowthBook<AppFeatures>();

You can now reference the hook you created instead of the one from the official package:

import { useGrowthBook } from "@/src/utils/growthbook"

const growthbook = useGrowthBook();

growthbook.getFeatureValue(knownKey, defaultValueOfValidType)

useFeatureIsOn<T>()

The React SDK also provides access to a type-safe useFeatureIsOn<AppFeatures>() hook.

const isDarkModeOn = useFeatureIsOn<AppFeatures>("dark_mode");

This will only allow you to pass known keys to the hook.

You can reduce the boilerplate for this hook by creating your own and using that instead:

// ./src/utils/growthbook.ts
import { useFeatureIsOn as _useFeatureIsOn } from "@growthbook/growthbook-react";

export const useFeatureIsOn = (id: keyof AppFeatures & string): boolean =>
_useFeatureIsOn<AppFeatures>(id);

And then reference the hook you created instead of the one from the official package:

import { useFeatureIsOn } from "@/src/utils/growthbook"

const isDarkModeOn = useFeatureIsOn("dark_mode");

Examples