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在请求过程中的任意时间,onErrorOccurred 可以被触发。虽然有时候触发的事件顺序不同,举个例子,在火狐浏览器中的HSTS过程,在onBeforeRequest事件执行后,onBeforeRedirect 事件会被立即触发。

所有的事件,接受onErrorOccurred事件, addListener()有三个参数 :

  • 监听本身
  • 一个filter 对象, 所以你仅可以被特定请求或特定的资源类型提醒
  • 一个可选的extraInfoSpec对象. 你可以使用这个对象添加特定的事件命令

这个监听函数接收一个details对象,这个对象包含这个请求的信息。他包含一个请求ID, 在插件中这个ID可以关联唯一个请求事件. 这个ID是浏览器会话和插件上下文中唯一的。他始终在同一个请求中,贯穿着转发和授权等事件中。

在一个给定的主机上使用webRequest API, 你必须有这个主机的相关权限,包括"webRequest" API permission 和 host permission. 为了使用 "blocking" 特性,你必须有 "webRequestBlocking" API 权限。

这个webRequest API不能让你进入一些安全敏感的请求,比如update checks and OCSP checks.

Modifying requests

在下边这些事件中,你可以修改请求. Specifically, you can:

To do this, you need to pass an option with the value "blocking" in the extraInfoSpec argument to the event's addListener(). This makes the listener synchronous. In the listener, you can then return a BlockingResponse object, which indicates the modification you need to make: for example, the modified request header you want to send.

From Firefox 52 onwards, instead of returning BlockingResponse, the listener can return a Promise which is resolved with a BlockingResponse. This enables the listener to process the request asynchronously.


Represents a particular kind of resource fetched in a web request.
An object describing filters to apply to webRequest events.
An array of HTTP headers. Each header is represented as an object with two properties: name and either value or binaryValue.

An object of this type is returned by event listeners that have set "blocking" in their extraInfoSpec argument. By setting particular properties in BlockingResponse, the listener can modify network requests.

Contains data uploaded in a URL request.


The maximum number of times that handlerBehaviorChanged() can be called in a 10 minute period.


This function can be used to ensure that event listeners are applied correctly when pages are in the browser's in-memory cache.


Fired when a request is about to be made, and before headers are available. This is a good place to listen if you want to cancel or redirect the request.
Fired before sending any HTTP data, but after HTTP headers are available. This is a good place to listen if you want to modify HTTP request headers.
Fired just before sending headers. If your add-on or some other add-on modified headers in onBeforeSendHeaders, you'll see the modified version here.
Fired when the HTTP response headers associated with a request have been received. You can use this event to modify HTTP response headers.
Fired when the server asks the client to provide authentication credentials. The listener can do nothing, cancel the request, or supply authentication credentials.
Fired when the first byte of the response body is received. For HTTP requests, this means that the status line and response headers are available.
Fired when a server-initiated redirect is about to occur.
Fired when a request is completed.
Fired when an error occurs.

Browser compatibility

ChromeEdgeFirefoxFirefox for AndroidOpera
BlockingResponse Yes Yes4548 Yes
HttpHeaders Yes Yes4548 Yes
RequestFilter Yes Yes4548 Yes
ResourceType44 No454831
StreamFilter No No5757 No
UploadData Yes Yes4548 Yes
filterResponseData No No5757 No
handlerBehaviorChanged Yes Yes4548 Yes
onAuthRequired Yes Yes54 *54 * Yes
onBeforeRedirect Yes Yes4648 Yes
onBeforeRequest Yes * Yes *46 *48 * Yes *
onBeforeSendHeaders Yes * Yes *45 *48 * Yes *
onCompleted Yes Yes4548 Yes
onErrorOccurred Yes Yes4548 Yes
onHeadersReceived Yes * Yes *45 *48 * Yes *
onResponseStarted Yes Yes4548 Yes
onSendHeaders Yes Yes4548 Yes

Edge incompatibilities

Promises are not supported in Edge. Use callbacks instead.

Chrome incompatibilities


  • In Firefox requests can be redirected only if their original URL uses the http: or https: scheme.
  • In Firefox, events are not fired for system requests (for example, extension upgrades or searchbar suggestions). From Firefox 57 onwards, Firefox makes an exception for extensions that need to intercept webRequest.onAuthRequired for proxy authorization. See the documentation for webRequest.onAuthRequired.
  • In Firefox, if an extension wants to redirect a public (e.g. HTTPS) URL to an extension page, the extension's manifest.json file must contain a web_accessible_resources key that lists the URL for the extension page. Note that any website may then link or redirect to that url, and extensions should treat any input (POST data, for examples) as if it came from an untrusted source, just as a normal web page should.

Example extensions


This API is based on Chromium's chrome.webRequest API. This documentation is derived from web_request.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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