# async onAsync()

Registers the listener function as callback of the selected RPC event.

**Type**

`async onAsync(eventName, listener): void`

**Parameters**

| Name      | Type      | Description                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| --------- | --------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| eventName | `String`  | Event to listen. Depeding on the provider chain one of [Constellation RPC event](https://2892156949-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FAUvaNviXuvMQPGFFlTu0%2Fuploads%2FlwMsSc6JGh3Hs9uhTPhW%2FconstellationRPCAPI?alt=media) or an [Ethereum RPC event](https://2892156949-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FAUvaNviXuvMQPGFFlTu0%2Fuploads%2FMUnqupiDBooRpr30wRuc%2FethereumRPCAPI?alt=media). |
| listener  | `()=>any` | Callback function.                                                                                                                                                                                                                                                                                                                                                                                                                                                  |

**Return Type**

`void`

**Example**

TypeScript

```typescript
await provider.onAsync("accountsChanged", () => {
  // Do something when accounts changed
});
```


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