***

id: 0c1e01c3-c188-41ad-beef-5c01507500c1
title: 'on'
slug: /node/reference/video/room-session/on
description: on method for the RoomSession class.
max-toc-depth: 3
----------------

### on

* **on**(`event`, `fn`)

Attaches an event handler to the specified event.

#### Parameters

| Name    | Type     | Description                                                                                                                     |
| :------ | :------- | :------------------------------------------------------------------------------------------------------------------------------ |
| `event` | `string` | Name of the event. See [Events](/docs/server-sdk/v3/node/reference/video/room-session/events) for the list of available events. |
| `fn`    | Function | An event handler.                                                                                                               |

#### Example

In the below example, we are listening for the `call.state` event and logging the current call state to the console.
This means this will be triggered every time the call state changes.

```js
call.on("call.state", (call) => {
    console.log("call state changed:", call.state);
});
```