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# once

> once method for the RoomSession class.

### once

* **once**(`event`, `fn`)

Attaches an event handler to the specified event. The handler will fire only once.

#### Parameters

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

> once method for the RoomSession class.