---
title: extension.onRequest
slug: Mozilla/Add-ons/WebExtensions/API/extension/onRequest
tags:
  - API
  - Add-ons
  - Event
  - Extension
  - Extensions
  - Non-standard
  - Reference
  - WebExtensions
  - onRequest
browser-compat: webextensions.api.extension.onRequest
---
{{AddonSidebar()}}

> **Warning:** This is not implemented in Firefox because it has been deprecated since Chrome 33. Please use [runtime.onMessage](/en-US/docs/Mozilla/Add-ons/WebExtensions/API/runtime/onMessage) instead.

Fired when a request is sent from either an extension process or a content script.

## Syntax

```js
chrome.extension.onRequest.addListener(function(
  request,         // optional any
  sender,          // runtime.MessageSender
  function() {...} // function
) {...})
chrome.extension.onRequest.removeListener(listener)
chrome.extension.onRequest.hasListener(listener)
```

Events have three functions:

- `addListener(callback)`
  - : Adds a listener to this event.
- `removeListener(listener)`
  - : Stop listening to this event. The `listener` argument is the listener to remove.
- `hasListener(listener)`
  - : Check whether `listener` is registered for this event. Returns `true` if it is listening, `false` otherwise.

## addListener syntax

### Parameters

- `callback`

  - : Function that will be called when this event occurs. The function will be passed the following arguments:

    - `request`
      - : `any`. The request sent by the calling script.

    <!---->

    - `sender`
      - : {{WebExtAPIRef('runtime.MessageSender')}}.

    <!---->

    - `sendResponse`
      - : `function`. Function to call (at most once) when you have a response. The argument should be any JSON-ifiable object, or undefined if there is no response. If you have more than one `onRequest` listener in the same document, then only one may send a response.

## Browser compatibility

{{Compat}}

{{WebExtExamples}}

> **Note:** This API is based on Chromium's [`chrome.extension`](https://developer.chrome.com/extensions/extension#event-onRequest) API. This documentation is derived from [`extension.json`](https://chromium.googlesource.com/chromium/src/+/master/chrome/common/extensions/api/extension.json) in the Chromium code.
>
> Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

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