> For the complete documentation index, see [llms.txt](https://docs.hackle.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.hackle.io/en/development-guide/react.md).

# React

{% hint style="info" %}
The Hackle React SDK supports React version 16.8 and above.

The React SDK is built on top of the [JavaScript SDK](/en/development-guide/javascript.md).
{% endhint %}

## Add Dependency

[![](https://img.shields.io/npm/v/%40hackler%2Freact-sdk)](https://www.npmjs.com/package/@hackler/react-sdk)

{% tabs %}
{% tab title="NPM" %}

```shell
npm install --save @hackler/react-sdk
```

{% endtab %}

{% tab title="YARN" %}

```shell
yarn add @hackler/react-sdk
```

{% endtab %}
{% endtabs %}

## SDK Initialization

You must initialize `HackleReactSDKClient` before using the SDK.

* `HackleReactSDKClient` is the class that provides methods for using SDK features.
* You can find the SDK Key in [SDK Integration Info](https://dashboard.hackle.io/config/sdk-setting) on the Hackle Dashboard.

During the application initialization phase, the SDK communicates with the Hackle server to sync data. This typically takes only a few milliseconds. Rendering begins immediately after synchronization is complete.

{% hint style="warning" %}
**Do not call SDK features before initialization is complete.**

Initialization runs asynchronously and is only complete once synchronization with the Hackle server has finished. If you call SDK features before initialization is complete, the SDK may not work correctly or events may be lost.

* **A/B Tests, Feature Flags, and Remote Config do not work correctly.** Instead of the actual assignment result, they return the default group (`A`), off (`false`), or the default value passed in the call. (Reason: `SDK_NOT_READY`)
* **Exposure events are not recorded.** Even if a user was actually part of the experiment, they are not counted as exposed, which can distort the experiment results.
* **Events may be lost.** Events collected with `track()` may not be sent.
* **Events may carry an inaccurate session ID.**
* **In-App Messages are not displayed.** Trigger conditions are evaluated at the moment an event is collected, and events collected before initialization is complete are not re-evaluated afterwards.

Make sure to call SDK features only after initialization is complete.
{% endhint %}

{% hint style="warning" %}
Note when using Google Tag Manager (GTM)

When integrating via GTM, you need to initialize the Hackle SDK and add it to the window object so that the SDK can be accessed from GTM.
{% endhint %}

{% tabs %}
{% tab title="React" %}

```javascript
import { createInstance, HackleProvider } from "@hackler/react-sdk";

// YOUR_BROWSER_SDK_KEY 자리에 SDK 키를 넣습니다.
const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY")

ReactDOM.render(
  <HackleProvider hackleClient={hackleClient}>
    <YourApp />
  </HackleProvider>,
  document.getElementById('root')
);

// GTM 연동 시 추가 script
window.hackleClient = hackleClient
```

{% endtab %}

{% tab title="Next.js" %}

```javascript
import {createInstance, HackleProvider} from "@hackler/react-sdk";

// YOUR_BROWSER_SDK_KEY 자리에 SDK 키를 넣습니다.
const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY")

function MyApp({Component, pageProps}) {
  return (
    <HackleProvider hackleClient={hackleClient} supportSSR>
      <Component {...pageProps} />
    </HackleProvider>
  )
}

export default MyApp
```

{% endtab %}

{% tab title="Gatsby" %}

```javascript
import {createInstance, HackleProvider} from "@hackler/react-sdk";

// YOUR_BROWSER_SDK_KEY 자리에 SDK 키를 넣습니다.
const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY")

function App() {
  return (
    <HackleProvider hackleClient={hackleClient} supportSSR>
      <YourApp />
    </HackleProvider>
  )
}

export default App
```

{% endtab %}
{% endtabs %}

### SDK Initialization Config

You can initialize the SDK with configuration options.

{% tabs %}
{% tab title="React" %}

```javascript
import { createInstance, HackleProvider } from "@hackler/react-sdk";

// 설정정보를 포함하여 초기화
const config = {
  debug: true
};

const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY", config);

ReactDOM.render(
  <HackleProvider hackleClient={hackleClient}>
    <YourApp />
  </HackleProvider>,
  document.getElementById('root')
);
```

{% endtab %}

{% tab title="Next.js" %}

```javascript
import {createInstance, HackleProvider} from "@hackler/react-sdk";

// 설정정보를 포함하여 초기화
const config = {
  debug: true
};

const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY", config);

function MyApp({Component, pageProps}) {
  return (
    <HackleProvider hackleClient={hackleClient} supportSSR>
      <Component {...pageProps} />
    </HackleProvider>
  )
}

export default MyApp
```

{% endtab %}
{% endtabs %}

#### All Configuration Options

<table data-full-width="false"><thead><tr><th width="213.57">Option</th><th width="295.49">Description</th><th width="125.81">Default</th><th width="108.1">Supported Version</th></tr></thead><tbody><tr><td><code>debug</code></td><td>Prints logs for all features to the console.</td><td><code>false</code></td><td>1.0.0+</td></tr><tr><td><code>pollingIntervalMillis</code></td><td>Periodically updates the configuration set in the Dashboard.<br>Minimum: 60000 (60 seconds)</td><td><code>-1</code></td><td>11.1.0+</td></tr><tr><td><code>exposureEventDedupIntervalMillis</code></td><td>Removes duplicate exposure events for the same A/B Test or Feature Flag distribution result triggered by the same user consecutively.<br>Minimum: 1000 (1 second)<br>Maximum: 3600000 (1 hour)</td><td><p><code>60000</code> (1 min / 11.23.0+)</p><p><code>-1</code> (no dedup / below 11.23.0)</p></td><td>11.1.0+</td></tr><tr><td><code>sessionTimeoutMillis</code> (deprecated)</td><td>Sets the session expiration time. Please use <code>sessionPolicy</code> instead.</td><td><code>1800000</code> (30 min)</td><td>11.8.0+</td></tr><tr><td><code>devTool</code></td><td>Enables <a href="/en/development-guide/react/react-user-explorer.md">User Explorer</a>.</td><td><code>undefined</code></td><td>11.13.0+</td></tr><tr><td><code>autoOpenDevTool</code></td><td>Option to automatically show the User Explorer button.</td><td><code>false</code></td><td>11.13.0+</td></tr><tr><td><code>user</code></td><td>Injects a user at initialization time.</td><td><code>undefined</code></td><td>11.22.3+</td></tr><tr><td><code>sessionPolicy</code></td><td>Configures session persistence and expiration conditions.</td><td><p><code>ALWAYS_NEW_SESSION</code> ,</p><p><code>1800000</code></p></td><td>11.54.0+</td></tr><tr><td><code>optOutTracking</code></td><td>Whether opt-out is enabled.</td><td><code>false</code></td><td>11.54.0+</td></tr><tr><td><code>evaluationMode</code></td><td>Configures the evaluation mode.</td><td><code>local</code></td><td>12.0.0+</td></tr></tbody></table>

#### Evaluation Mode Configuration

You can choose whether the SDK performs evaluation itself or fetches results that the Hackle server has already evaluated.\
If not configured, the default value `"local"` (local evaluation) is used.

```javascript
import { createInstance, HackleProvider } from "@hackler/react-sdk";

const config = {
    evaluationMode: "remote"
};

const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY", config);

ReactDOM.render(
  <HackleProvider hackleClient={hackleClient}>
    <YourApp />
  </HackleProvider>,
  document.getElementById('root')
);
```

{% hint style="warning" %}
When you use remote evaluation, user information is not stored in the browser. If user information was already stored while using local evaluation, it is deleted.

For the differences between the two modes and how to choose between them, refer to the [Evaluation Mode](/en/development-guide/sdk/evaluation-mode.md) documentation.
{% endhint %}

#### Session Policy Configuration

You can configure session persistence and expiration conditions using the session policy.

```javascript
import { createInstance, HackleProvider, HackleSessionPersistConditions } from "@hackler/react-sdk";

const config = {
    sessionPolicy: {
        timeoutMillis: 3600000,
        persistCondition: HackleSessionPersistConditions.NULL_TO_USER_ID
    }
};

const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY", config);

ReactDOM.render(
  <HackleProvider hackleClient={hackleClient}>
    <YourApp />
  </HackleProvider>,
  document.getElementById('root')
);
```

#### Injecting User at Initialization

When `user` is set in config, you can initialize the SDK with user information included.

* If no user information is provided, the user information stored in cookies is used.
* If user information is provided, the user information stored in cookies is not used.
* If there is no user information in cookies, a user with the Hackle Device ID as the device id is used.

{% hint style="info" %}
You can freely update user information after SDK initialization using the user information setter functions.
{% endhint %}

{% hint style="warning" %}
The user information injected at initialization and the user information stored in cookies are not merged.

e.g.) If `userId: A` is stored in cookies and you inject `deviceId: B` at initialization, the user is set to `userId: null, deviceId: B`.
{% endhint %}

{% hint style="warning" %}
As of React SDK 12.0.0, the `user` prop of `HackleProvider` is applied only when its value changes, and when applied it replaces the existing user information instead of merging it.

If you use both the `user` prop and the user information setter functions (`setUser`, `setUserId`, `setDeviceId`, and so on), user information can be lost. Use only one of the two approaches. If you only need the initial user information, we recommend using `user` in config instead of the `user` prop.
{% endhint %}

{% tabs %}
{% tab title="React" %}

```javascript
import { createInstance, HackleProvider } from "@hackler/react-sdk";

const user = {
  userId: "LOGIN_ID",
  deviceId: "CUSTOM_DEVICE_ID"
};

const config = {
  debug: true,
  user: user
};

const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY", config);

ReactDOM.render(
  <HackleProvider hackleClient={hackleClient}>
    <YourApp />
  </HackleProvider>,
  document.getElementById('root')
);
```

{% endtab %}

{% tab title="Next.js" %}

```javascript
import {createInstance, HackleProvider} from "@hackler/react-sdk";

const user = {
  userId: "LOGIN_ID",
  deviceId: "CUSTOM_DEVICE_ID"
};

const config = {
  debug: true,
  user: user
};

const hackleClient = createInstance("YOUR_BROWSER_SDK_KEY", config);

function MyApp({Component, pageProps}) {
  return (
    <HackleProvider hackleClient={hackleClient} supportSSR>
      <Component {...pageProps} />
    </HackleProvider>
  )
}

export default MyApp
```

{% endtab %}
{% endtabs %}

### Refreshing Dashboard Configuration

You can explicitly refresh the Dashboard configuration.

{% hint style="warning" %}
This function can only be called once every 60 seconds.
{% endhint %}

```javascript
await hackleClient.fetch();
```

As of React SDK 12.0.0, hooks such as `useVariation` are re-evaluated based on the latest configuration after `fetch()` completes.


---

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