Skip to main content
Source code: statsig-io/js-client-monorepo

​
Setup the SDK

1

Install the SDK

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 are not already in your project.
npx expo install expo-device expo-application @react-native-async-storage/async-storage
2

Initialize the SDK

Next, initialize the SDK with a client SDK key from the “API Keys” tab on the Statsig console. These keys are safe to embed in a client application.Along with the key, pass in a User Object 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. 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 instead of LocalStorage (which isn’t available in RN environments).
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>
  );
}
Avoid iOS 18.4 on Simulator: Apple introduced a networking bug in iOS 18.4 that causes requests to fail when running in the Simulator. For more details, see this thread on Apple’s forums.

​
Use the SDK

You can get an instance of the StatsigClient to check gates, experiments, dynamic configs, layers, and log events. 
import { useStatsigClient } from "@statsig/expo-bindings";

const { client } = useStatsigClient();
See the methods you can call on the client below.

​
Checking a Feature Flag/Gate

Now that your SDK is initialized, let’s check a Feature Gate. 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 
const { client } = useStatsigClient();
return (
  <div>Gate is {client.checkGate('check_user') ? 'passing' : 'failing'}.</div>
);

​
Reading a Dynamic Config

Feature Gates can be very useful for simple on/off switches, with optional but advanced user targeting. However, if you want to be able send a different set of values (strings, numbers, and etc.) to your clients based on specific user attributes, e.g. country, Dynamic Configs can help you with that. The API is very similar to Feature Gates, but you get an entire json object you can configure on the server and you can 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 
const { client } = useStatsigClient();
const config = client.getConfig('app_properties');

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

​
Getting a Layer/Experiment

Then we have Layers/Experiments, which you can use to run A/B/n experiments. We offer two APIs, but we recommend the use of layers to enable 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. 
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. 
const { client } = useStatsigClient();
const layer = client.getLayer('homepage_layer');

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

​
Logging an Event

Now that you have a Feature Gate or an Experiment set up, you may want to track some custom events and see how your new features or different experiment groups affect these events. This is super easy with Statsig - simply call the Log Event API for the event, and you can additionally provide some value and/or an object of metadata to be logged together with the event: You can get the client with the useStatsigClient hook, and then call logEvent 
const { client } = useStatsigClient();
return <button onClick={() => client.logEvent("button_click")}>Click Me</button>

​
Loading State

Dependent on your setup, you may want to wait for the latest values before checking a gate or experiment. If you are using StatsigProviderExpo, you can pass in a loadingComponent prop to display a loading state while the SDK is initializing. If you are using the useClientAsyncInitExpo hook, you can check the isLoading prop to determine if the SDK is still loading.
  • StatsigProviderExpo
  • useClientAsyncInitExpo
export function App() {
  const loadingComponent = <div>Loading...</div>;

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

​
Advanced

​
Expo Without React

In some scenarios, you may need to use the StatsigClient when you are not in the React component tree. Things like background tasks or handling notifications. For these, you can use the Expo specific StatsigClientExpo. 
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 utilizing MMKV in your project, and would prefer to use that instead of the default (AsyncStorage). You can provide you own StorageProvider via StatsigOptions. Something like: 
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 a ERROR: A networking error occured during POST request messages when first initializing Statsig. This issue is solved in releases of the SDK after 3.1.0, so upgrading your SDK should solve the issue. If it persists, reach out to us in Slack.
⌘I