## Set up the SDK

{% steps %}
{% step title="Install the SDK" %}
```shell
npx expo install @statsig/expo-bindings
```

### Peer Dependencies

The `@statsig/expo-bindings` package has peer dependencies which may also need to be installed if they aren't already in your project.

```shell
npx expo install expo-device expo-application @react-native-async-storage/async-storage
```
{% /step %}

{% step title="Initialize the SDK" %}
Next, initialize the SDK with a client SDK key from the ["API Keys" tab on the Statsig console](https://console.statsig.com/api_keys). These keys are safe to embed in a client application.

Along with the key, pass in a [User Object](#statsig-user) with the attributes you'd like to target later on in a gate or experiment.

The setup for an Expo environment is very similar to a plain [React environment](/client/React).
The only difference is that you need to use the Expo specific `StatsigProviderExpo`.
This automatically switches out the storage layer used by the SDK, utilizing [AsyncStorage](https://github.com/react-native-async-storage) instead of LocalStorage (which isn't available in RN environments).

```tsx
import { StatsigProviderExpo, useFeatureGate } from "@statsig/expo-bindings";

function Content() {
  const gate = useFeatureGate("a_gate");

  return <Text>Reason: {gate.details.reason}</Text>; // Reason: Network or NetworkNotModified
}

function App() {
  return (
    <StatsigProviderExpo
      sdkKey={YOUR_CLIENT_KEY}
      user={{ userID: "a-user" }}
      options={{ environment: { tier: "development" } }} // (Optional)
      loadingComponent={<Text>Loading...</Text>}
    >
      <Content />
    </StatsigProviderExpo>
  );
}
```
{% /step %}
{% /steps %}

## Use the SDK

You can get an instance of the StatsigClient to check gates, experiments, dynamic configs, layers, and log events.

```jsx
import { useStatsigClient } from "@statsig/expo-bindings";

const { client } = useStatsigClient();
```

The methods you can call on the client are listed below.

### Checking a Feature Flag/Gate

Now that your SDK is initialized, let's check a [**Feature Gate**](/feature-flags/overview). Feature Gates can be used to create logic branches in code that can be rolled out to different users from the Statsig Console. Gates are always **CLOSED** or **OFF** (think `return false;`) by default.

You can evaluate a gate by getting the client with the `useStatsigClient` hook, and then calling `checkGate`

```tsx
const { client } = useStatsigClient();
return (
  <div>Gate is {client.checkGate('check_user') ? 'passing' : 'failing'}.</div>
);
```

### Reading a Dynamic Config

Feature Gates are useful for simple on/off switches with optional advanced user targeting. To send a different set of values (strings, numbers, etc.) to clients based on specific user attributes such as country, use **Dynamic Configs**. The API is similar to Feature Gates, but you get a complete JSON object you can configure on the server and fetch typed parameters from it. For example:

You can get a DynamicConfig value by getting the client with the `useStatsigClient` hook, and then calling `getConfig`

```tsx
const { client } = useStatsigClient();
const config = client.getConfig('app_properties');

return (
  <div>{config.get('title', 'Default Title')}</div>
);
```

### Getting a Layer/Experiment

**Layers/Experiments** let you run A/B/n experiments. Two APIs are available, but Statsig recommends [layers](/experiments/layers-overview) for quicker iterations with parameter reuse.

You can access the experiment variant and parameters for the user by getting the client with the `useStatsigClient` hook, and then calling `getExperiment`.

```tsx
const { client } = useStatsigClient();
const experiment = client.getExperiment('headline_test');

return (
  <div>Headline Parameter: {experiment.get('headline', 'Default')}.</div>
);
```

You can access layers and layer parameters for the user by getting the client with the `useStatsigClient` hook, and then calling `getLayer`.

```tsx
const { client } = useStatsigClient();
const layer = client.getLayer('homepage_layer');

return (
  <div>Headline Parameter: {layer.get('hero_text', 'Welcome')}.</div>
);
```

### Logging an Event

After setting up a Feature Gate or Experiment, you may want to track custom events to see how new features or experiment groups affect those events. Call the Log Event API for the event. You can also provide a value and metadata object to be logged with the event.

Get the client with the `useStatsigClient` hook, then call `logEvent`:

```tsx
const { client } = useStatsigClient();
return <button onClick={() => client.logEvent("button_click")}>Click Me</button>
```

### Flushing Logged Events

`flush()` sends queued events immediately. Use `shutdown()` when your app is exiting.

```tsx
import { Button } from 'react-native';
import { useStatsigClient } from '@statsig/expo-bindings';

const { client } = useStatsigClient();

return (
  <button
    onClick={async () => {
      await client.flush();
    }}
  >
    Flush Events
  </button>
);
```

## Loading State

Depending on your setup, you may want to wait for the latest values before checking a gate or experiment. If you are using `StatsigProviderExpo`, pass in a `loadingComponent` prop to display a loading state while the SDK is initializing. If you are using the `useClientAsyncInitExpo` hook, check the `isLoading` prop to determine if the SDK is still loading.

{% tabs %}
{% tab title="StatsigProviderExpo" %}
```tsx
export function App() {
  const loadingComponent = <div>Loading...</div>;

  return (
    <StatsigProviderExpo
      ...
      loadingComponent={loadingComponent} // <- Pass in the loading component
    >
        <YourComponent />
    </StatsigProviderExpo>
  );
}
```
{% /tab %}

{% tab title="useClientAsyncInitExpo" %}
```tsx
export function App() {
  const { client, isLoading } = useClientAsyncInitExpo(...);

  if (isLoading) {
    return <div>Loading...</div>;
  }

  return (
    <StatsigProviderExpo client={client}>
      <YourComponent />
    </StatsigProviderExpo>
  );
}
```
{% /tab %}
{% /tabs %}

## Lifecycle & Advanced Usage

## Shutting Statsig Down

The SDK keeps event logs in the client cache and flushes them periodically to save data and battery usage. Because of this, the SDK may not have flushed some events when your app shuts down.

To ensure all logged events are flushed or saved locally, shut down Statsig when your app is closing:

```tsx
import { useEffect } from 'react';
import { useStatsigClient } from '@statsig/expo-bindings';

const { client } = useStatsigClient();

useEffect(() => {
  return () => {
    void client.shutdown();
  };
}, [client]);
```

## Advanced

### Expo Without React

In some scenarios, you may need to use the `StatsigClient` outside the React component tree. For example, in background tasks or notification handlers, use the Expo-specific `StatsigClientExpo`.

```tsx
import { StatsigClientExpo } from '@statsig/expo-bindings';

const myClient = new StatsigClientExpo(
  YOUR_CLIENT_KEY,
  { userID: "a-user" }
);

await myClient.initializeAsync();

if (myClient.checkGate("my_gate")) {
  // do something cool
}
```

### Synchronous Storage with MMKV

If you are using [MMKV](https://github.com/mrousavy/react-native-mmkv) in your project and prefer it over the default ([AsyncStorage](https://github.com/react-native-async-storage)), provide your own `StorageProvider` through `StatsigOptions`.

```tsx
import { MMKV } from "react-native-mmkv";
import { StorageProvider } from "@statsig/client-core";
import { StatsigProviderExpo } from "@statsig/expo-bindings";

function App() {
    const [storageProvider] = useState<StorageProvider>(() => {
      const mmkv = new MMKV();

      return {
        isReady: () => true,
        isReadyResolver: () => null,
        getProviderName: () => "MMKV",
        getAllKeys: () => mmkv.getAllKeys(),
        getItem: (key: string) => mmkv.getString(key) ?? null,
        setItem: (key: string, value: string) => mmkv.set(key, value),
        removeItem: (key: string) => mmkv.delete(key),
      };
    });

   return (
    <StatsigProviderExpo
      sdkKey={YOUR_CLIENT_KEY}
      user={{ userID: "a-user" }}
      options={{
        storageProvider, // <- Passed into StatsigOptions
      }}
    >
      <Text>...</Text>
    </StatsigProviderExpo>
   );
}
```

## Debugging

### Network Issues

Some users have reported `ERROR: A networking error occured during POST request` messages when first initializing Statsig. Statsig resolved this issue in SDK versions after 3.1.0. Upgrade your SDK to resolve the error. If the error persists, reach out through [Slack](https://statsig.com/slack).