***

id: 80050029-f408-4151-9f89-8df161d56d6c
title: once
slug: /node/reference/pubsub/client/once
description: once method for the Client class.
max-toc-depth: 3
----------------

### 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 [Events](/docs/server-sdk/v3/node/reference/pubsub/client/events) for the list of available events. |
| `fn`    | Function | An event handler.                                                                                                          |