webRequest.onErrorOccurred
Fired when a request could not be processed due to an error: for example, a lack of Internet connectivity.
The error is passed to the listener as the error
property of the details
object.
Note that this event is not fired for HTTP errors (4XX or 5XX responses): these will go through the normal stages of a request, calling any event listeners, and setting details.statusCode
to report the error.
This event is informational only.
Syntax
browser.webRequest.onErrorOccurred.addListener(
listener, // function
filter // object
)
browser.webRequest.onErrorOccurred.removeListener(listener)
browser.webRequest.onErrorOccurred.hasListener(listener)
Events have three functions:
addListener(listener, filter)
-
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. Returnstrue
if it is listening,false
otherwise.
addListener syntax
Parameters
listener
-
The function called when this event occurs. The function is passed this argument:
filter
-
webRequest.RequestFilter
. A filter that restricts the events that is sent to this listener.
Additional objects
details
-
string
. If the request is from a tab open in a contextual identity, the cookie store ID of the contextual identity. See Work with contextual identities for more information. documentUrl
-
string
. URL of the document in which the resource will be loaded. For example, if the web page at "https://example.com" contains an image or an iframe, then thedocumentUrl
for the image or iframe will be "https://example.com". For a top-level document,documentUrl
is undefined. error
-
string
. The error description. This string is an internal error string, may vary from one browser to another, and is not guaranteed to stay the same between releases. frameId
-
integer
. Zero if the request happens in the main frame; a positive value is the ID of a subframe in which the request happens. If the document of a (sub-)frame is loaded (type
ismain_frame
orsub_frame
),frameId
indicates the ID of this frame, not the ID of the outer frame. Frame IDs are unique within a tab. fromCache
-
boolean
. Indicates if this response was fetched from disk cache. incognito
-
boolean
. Whether the request is from a private browsing window. ip
-
string
. The IP address of the server the request was sent to. It may be a literal IPv6 address. method
-
string
. Standard HTTP method: for example, "GET" or "POST". originUrl
-
string
. URL of the resource which triggered the request. For example, if "https://example.com" contains a link, and the user clicks the link, then theoriginUrl
for the resulting request is "https://example.com".The
originUrl
is often but not always the same as thedocumentUrl
. For example, if a page contains an iframe, and the iframe contains a link that loads a new document into the iframe, then thedocumentUrl
for the resulting request will be the iframe's parent document, but theoriginUrl
will be the URL of the document in the iframe that contained the link. parentFrameId
-
integer
. ID of the frame that contains the frame which sent the request. Set to -1 if no parent frame exists. proxyInfo
-
object
. This property is present only if the request is being proxied. It contains the following properties:host
-
string
. The hostname of the proxy server. port
-
integer
. The port number of the proxy server. type
-
string
. The type of proxy server. One of:- "http": HTTP proxy (or SSL CONNECT for HTTPS)
- "https": HTTP proxying over TLS connection to proxy
- "socks": SOCKS v5 proxy
- "socks4": SOCKS v4 proxy
- "direct": no proxy
- "unknown": unknown proxy
username
-
string
. Username for the proxy service. proxyDNS
-
boolean
. True if the proxy will perform domain name resolution based on the hostname supplied, meaning that the client should not do its own DNS lookup. failoverTimeout
-
integer
. Failover timeout in seconds. If the proxy connection fails, the proxy will not be used again for this period.
requestId
-
string
. The ID of the request. Request IDs are unique within a browser session, so you can use them to relate different events associated with the same request. tabId
-
integer
. The ID of the tab in which the request takes place. Set to -1 if the request isn't related to a tab. thirdParty
-
boolean
. Indicates whether the request and its content window hierarchy are third party. timeStamp
-
number
. The time when this event fired, in milliseconds since the epoch. type
-
webRequest.ResourceType
. The type of resource being requested: for example, "image", "script", "stylesheet". url
-
string
. Target of the request. urlClassification
-
object
. The type of tracking associated with the request, if the request is classified by Firefox Tracking Protection. This is an object with these properties:firstParty
-
array
ofstrings
. Classification flags for the request's first party. thirdParty
-
array
ofstrings
. Classification flags for the request or its window hierarchy's third parties.
The classification flags include:
fingerprinting
andfingerprinting_content
: indicates the request is involved in fingerprinting ("an origin found to fingerprint").fingerprinting
indicates the domain is in the fingerprinting and tracking category. Examples of this type of domain include advertisers who want to associate a profile with the visiting user.fingerprinting_content
indicates the domain is in the fingerprinting category but not the tracking category. Examples of this type of domain include payment providers who use fingerprinting techniques to identify the visiting user for anti-fraud purposes.
cryptomining
andcryptomining_content
: similar to the fingerprinting category but for cryptomining resources.tracking
,tracking_ad
,tracking_analytics
,tracking_social
, andtracking_content
: indicates the request is involved in tracking.tracking
is any generic tracking request, thead
,analytics
,social
, andcontent
suffixes identify the type of tracker.any_basic_tracking
: a meta flag that combines tracking and fingerprinting flags, excludingtracking_content
andfingerprinting_content
.any_strict_tracking
: a meta flag that combines all tracking and fingerprinting flags.any_social_tracking
: a meta flag that combines all social tracking flags.
Note If Firefox Tracking Protection blocks the request an empty object is returned and
error
returns one of these codes:NS_ERROR_MALWARE_URI
indicating a malware URI.NS_ERROR_PHISHING_URI
indicating a phishing URI.NS_ERROR_TRACKING_URI
indicating a tracking URI.NS_ERROR_UNWANTED_URI
indicating an unwanted URI.NS_ERROR_BLOCKED_URI
indicating a blocked URI.NS_ERROR_HARMFUL_URI
indicating a harmful URI.NS_ERROR_FINGERPRINTING
indicating a fingerprinting URI.NS_ERROR_CRYPTOMINING_URI
indicating a cryptomining URI.NS_ERROR_SOCIALTRACKING_URI
indicating a social tracking URI.
Browser compatibility
BCD tables only load in the browser
Examples
let target = "<all_urls>";
/*
e.g., with no network:
"https://developer.mozilla.org/en-US/"
NS_ERROR_NET_ON_RESOLVED in Firefox
net::ERR_INTERNET_DISCONNECTED in Chrome
*/
function logError(responseDetails) {
console.log(responseDetails.url);
console.log(responseDetails.error);
}
browser.webRequest.onErrorOccurred.addListener(logError, { urls: [target] });
Example extensions
Note: This API is based on Chromium's chrome.webRequest
API. This documentation is derived from web_request.json
in the Chromium code.