# Using the Custom Module in Wallet API Client

The Custom Module allows you to interact with any Custom Handler supported by the server.

## Custom Module Overview

> **Note:** We are still working on improving the type safety of custom modules

### Step 1

First, you need a Custom Module, you can import one from another lib or create it.

To create a Custom Module, you need to import and extend the CustomModule class.

You can add any method you want in your class and do any logic you need to.\
Use `this.request<ParamType, ReturnType>("custom.handler", param)` to call the Custom Handler methods supported by the server.

```javascript
import { CustomModule } from "@ledgerhq/wallet-api-client";

type CustomLogHandlersType = {
  "custom.log": (message: string) => Promise<{ res: "hello" }>;
};

class CustomLog extends CustomModule {
  log(message: string) {
    return this.request<
      Parameters<CustomLogHandlersType["custom.log"]>[0],
      ReturnType<CustomLogHandlersType["custom.log"]>
    >("custom.log", message);
  }
}
```

### Step 2

Go back to your transport declaration from your [Wallet API Configuration](../configuration).

You need to adapt the WalletAPIClient by passing a function that returns your custom handler.

> **Note:** You can use the `defaultLogger` export from the `@ledgerhq/wallet-api-client`
> if you weren't using the second parameter of the WalletAPIClient

```javascript
import { WalletAPIClient, defaultLogger } from "@ledgerhq/wallet-api-client";

const walletApiClient = new WalletAPIClient(
  transport,
  defaultLogger,
  (client) => {
    return new CustomLog(client);
  }
);
```

> **Note:** You can also use multiple Custom Module in an object.

```javascript
import { WalletAPIClient, defaultLogger } from "@ledgerhq/wallet-api-client";

const walletApiClient = new WalletAPIClient(
  transport,
  defaultLogger,
  (client) => {
    return {
      log: new CustomLog(client),
      log2: new CustomLog2(client),
      device: new CustomDevice(client),
    };
  }
);
```

### Step 3

Access the Custom Module via `walletApiClient.custom`.

```javascript
// Example using one module
const res = await walletApiClient.custom.log("test");
// Example using multiple modules
const res2 = await walletApiClient.custom.log.log("test");
```

## Handling Errors

Make sure to handle errors gracefully and provide appropriate feedback to the user.\
Additionally, always remember to disconnect the `WindowMessageTransport` when you're done interacting with the  API to free up resources.