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id: cfeac22a-42c5-45b2-b7d8-e37bd486b48d
title: once
slug: /js/reference/chat/client/once
max-toc-depth: 3
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* **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/chat/client/events). |
| `fn`    | Function | An event handler.                                                                                  |