webRequest.onErrorOccurred

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. Returns true if it is listening, false otherwise.

addListener syntax

Parameters

listener

The function called when this event occurs. The function is passed this argument:

details

object. Details about the request. See the details section for more information.

filter

webRequest.RequestFilter. A filter that restricts the events that is sent to this listener.

Additional objects

details

cookieStoreId

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 the documentUrl 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 is main_frame or sub_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 the originUrl for the resulting request is "https://example.com".

The originUrl is often but not always the same as the documentUrl. For example, if a page contains an iframe, and the iframe contains a link that loads a new document into the iframe, then the documentUrl for the resulting request will be the iframe's parent document, but the originUrl 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 of string. Classification flags for the request's first party.

thirdParty

array of string. Classification flags for the request or its window hierarchy's third parties.

The classification flags include:

• fingerprinting and fingerprinting_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 and cryptomining_content: similar to the fingerprinting category but for cryptomining resources.
• tracking, tracking_ad, tracking_analytics, tracking_social, and tracking_content: indicates the request is involved in tracking. tracking is any generic tracking request, the ad, analytics, social, and content suffixes identify the type of tracker.
• emailtracking and emailtracking_content: indicates the request is involved in tracking emails.
• any_basic_tracking: a meta flag that combines tracking and fingerprinting flags, excluding tracking_content and fingerprinting_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.

You can find more information on tracker types on the disconnect.me website. The content suffix indicates trackers that track and serve content. Blocking them protects users but can lead to sites breaking or elements not being displayed.

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.

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

• stored-credentials

Browser compatibility