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The StatsigSpecsDataAdapter is the default SpecsDataAdapter used by a StatsigOnDeviceEvalClient instance. It handles fetching and caching values from Statsig’s servers. If required, you can create your own custom SpecsDataAdapter and provide it to the Statsig client via StatsigOptions.dataAdapter.

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Overview

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Synchronous Behavior (Cache)

When calling StatsigOnDeviceEvalClient.initializeSync, the StatsigSpecsDataAdapter will load values from Cache and provide them to the client. The client will also call refresh in the background via StatsigSpecsDataAdapter.getDataAsync, leading to values lagging until the next time initializeSync. In practice, this means that for the very first session, there will be no values, and not until the next session will the cache have values.

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Asynchronous Behavior (Network)

When calling StatsigOnDeviceEvalClient.initializeAsync, the StatsigSpecsDataAdapter will load values from Cache and provide them to the client. The client will then block on a call to StatsigSpecsDataAdapter.getDataAsync, allowing the ability to await the latest values from Statsig. If you want the latest values, but do not want to await the asynchronous call, you may call initializeAsync and simply .catch the promise. Note that this could lead to values changing mid-session as newer values arrive from the network.

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Advanced Usage

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Getting the Data Adapter

You can access the data adapter from your Statsig on-device client instance: 
const client = new StatsigOnDeviceEvalClient('client-key');
await client.initializeAsync();

const dataAdapter = client.dataAdapter;
```python

[View full example on GitHub](https://github.com/statsig-io/js-client-monorepo/blob/main/samples/react/src/samples/on-device-eval-client/sample-on-device-get-data-adapter.tsx)

### Bootstrapping

Bootstrapping allows you to provide the required data without a network call. This can be useful if you do not wish to make network calls during startup.

If you are building a mobile app and want to bundle values with your application. Then you can load the values from a local file at startup and provide them to the data adapter.

```typescript
import { StatsigOnDeviceEvalClient } from '@statsig/js-on-device-eval-client';

const client = new StatsigOnDeviceEvalClient('client-key');

// Bootstrap with specs data from local file or bundle
const specsData = /* data from local file */;
await client.dataAdapter.setData(specsData);

await client.initializeAsync();
```python

[View full example on GitHub](https://github.com/statsig-io/js-client-monorepo/blob/main/samples/react/src/samples/on-device-eval-client/sample-on-device-bootstrap.tsx)

<Note>
You can get a copy of your current specs data by visiting: `https://api.statsigcdn.com/v1/download_config_specs/client-{YOUR_SDK_KEY}.json`
</Note>

### Custom Implementation

If you would like to customize when and how data is fetched, as well as where it is stored, you can create your own class the conforms to the `SpecsDataAdapter` type.

The `SpecsDataAdapter` type outlines the following functions:

- `attach` - Called when the `SpecsDataAdapter` is passed into a `StatsigOnDeviceEvalClient` via `StatsigOptions`. This allows the `SpecsDataAdapter` to use
  the same SDK Key and `StatsigOptions` as the `StatsigOnDeviceEvalClient` instance.

  - ```typescript
    attach: (sdkKey: string, options: StatsigOptionsCommon | null) => void
    ```sql

- `getDataSync` - Synchronously get evaluation data for the given user. Called during initializeSync. It is also called during
  async update operations before StatsigDataAdapter.getDataAsync is called.

  - ```typescript
    getDataSync: () => DataAdapterResult | null;
    ```text

- `getDataAsync` - Asynchronously get evaluation data for the given user. Called during initializeAsync.

  - ```typescript
    getDataAsync: (current: DataAdapterResult | null) => Promise<DataAdapterResult | null>;
    ```text

- `prefetchData` - Manually trigger a fetch for new specs data.

  - ```typescript
    prefetchData: () => Promise<void>;
    ```text

- `setData` - Manually set specs data.

  - ```typescript
    setData: (data: string) => Promise<void>;