## Documentation Index

Fetch the complete documentation index at: [/llms.txt](https://docs.cognigy.com/llms.txt)

Use this file to discover all available pages before exploring further.

Adds an event listener for a specific event. See the [Event Reference](https://docs.cognigy.com/click-to-call/sdk/event-reference/overview) for all available events.

## Signature

```
client.on<T extends EventName>(event: T, callback: EventCallback<T>): this;
```

## Parameters

| Parameter | Type | Description | Required |
| --- | --- | --- | --- |
| `event` | `EventName` | The name of the event to listen for. | Yes |
| `callback` | `EventCallback<T>` | The callback function to invoke when the event is emitted. | Yes |

## Returns

`this` — the client instance, allowing method chaining.

## Example

```
client.on('answered', (session) => {
  console.log('Call answered:', session.id);
});

client.on('error', (error) => {
  console.error('SDK error:', error.message);
});
```

### Type-Safe Event Handling

```
import type { WebRTCClientEvents } from '@cognigy/click-to-call-sdk';

const handleAnswered: WebRTCClientEvents['answered'] = (session) => {
  console.log('Call answered:', session.id);
};

client.on('answered', handleAnswered);
```

## More Information

- [off](https://docs.cognigy.com/click-to-call/sdk/api-reference/off)
- [Event Reference](https://docs.cognigy.com/click-to-call/sdk/event-reference/overview)
- [WebRTCClientEvents](https://docs.cognigy.com/click-to-call/sdk/api-reference/types#webrtcclientevents)

Last modified on April 21, 2026.