chrome.declarativeContent

Description: Use the chrome.declarativeContent API to take actions depending on the content of a page, without requiring permission to read the page's content.
Availability: Since Chrome 33.
Permissions: "declarativeContent"
Learn More: Declarative Events
activeTab

Usage

The Declarative Content API allows you to show your extension's page action depending on the URL of a web page and the CSS selectors its content matches, without needing to take a host permission or inject a content script. Use the activeTab permission in order to be able to interact with a page after the user clicks on your page action.

If you need more precise control over when your page action appears or you need to change its appearance to match the current tab before the user clicks on it, you'll have to keep using the pageAction API.

Rules

As a declarative API, this API lets you register rules on the onPageChanged event object which take an action (ShowPageAction and SetIcon) when a set of conditions, represented as a PageStateMatcher, are met.

The PageStateMatcher matches web pages if and only if all listed criteria are met. The following rule would show a page action for pages on https://www.google.com/ when a password field is present on it: 

      var rule1 = {
        conditions: [
          new chrome.declarativeContent.PageStateMatcher({
            pageUrl: { hostEquals: 'www.google.com', schemes: ['https'] },
            css: ["input[type='password']"]
          })
        ],
        actions: [ new chrome.declarativeContent.ShowPageAction() ]
      };

Note: All conditions and actions are created via a constructor as shown in the example above.

In order to also show a page action for sites with a video, you can add a second condition, as each condition is sufficient to trigger all specified actions: 

      var rule2 = {
        conditions: [
          new chrome.declarativeContent.PageStateMatcher({
            pageUrl: { hostEquals: 'www.google.com', schemes: ['https'] },
            css: ["input[type='password']"]
          }),
          new chrome.declarativeContent.PageStateMatcher({
            css: ["video"]
          })
        ],
        actions: [ new chrome.declarativeContent.ShowPageAction() ]
      };

Added rules are saved across browser restarts, so register them as follows: 

      chrome.runtime.onInstalled.addListener(function(details) {
        chrome.declarativeContent.onPageChanged.removeRules(undefined, function() {
          chrome.declarativeContent.onPageChanged.addRules([rule2]);
        });
      });

Note: You should always register or unregister rules in bulk rather than individually because each of these operations recreates internal data structures. This re-creation is computationally expensive but facilitates a faster matching algorithm.

Combine the above rule with the activeTab permission to create an extension that doesn't need any install-time permissions but can invite the user to click its page action on relevant pages and can run on those pages when the user clicks the page action.

CSS Matching

PageStateMatcher.css conditions must be compound selectors, meaning that you can't include combinators like whitespace or ">" in your selectors. This helps Chrome match the selectors more efficiently.

Compound Selectors (OK)Complex Selectors (Not OK)
adiv p
iframe.special[src^='http']p>span.highlight
ns|*p + ol
#abcd:checkedp::first-line

CSS conditions only match displayed elements: if an element that matches your selector is display:none or one of its parent elements is display:none, it doesn't cause the condition to match. Elements styled with visibility:hidden, positioned off-screen, or hidden by other elements can still make your condition match.

Bookmarked State Matching

The PageStateMatcher.isBookmarked condition allows matching of the bookmarked state of the current URL in the user's profile. To make use of this condition the "bookmarks" permission must be declared in the extension manifest

Summary

Types
PageStateMatcherInstanceType
ShowPageActionInstanceType
SetIconInstanceType
RequestContentScriptInstanceType
PageStateMatcher
ShowPageAction
SetIcon
RequestContentScript
Events
onPageChanged

Types

PageStateMatcherInstanceType

Enum
"declarativeContent.PageStateMatcher"

ShowPageActionInstanceType

Enum
"declarativeContent.ShowPageAction"

SetIconInstanceType

Enum
"declarativeContent.SetIcon"

RequestContentScriptInstanceType

Enum
"declarativeContent.RequestContentScript"

PageStateMatcher

Matches the state of a web page based on various criteria.
properties
object (optional) pageUrl

Matches if the conditions of the UrlFilter are fulfilled for the top-level URL of the page.

string (optional) hostContains

Matches if the host name of the URL contains a specified string. To test whether a host name component has a prefix 'foo', use hostContains: '.foo'. This matches 'www.foobar.com' and 'foo.com', because an implicit dot is added at the beginning of the host name. Similarly, hostContains can be used to match against component suffix ('foo.') and to exactly match against components ('.foo.'). Suffix- and exact-matching for the last components need to be done separately using hostSuffix, because no implicit dot is added at the end of the host name.

string (optional) hostEquals

Matches if the host name of the URL is equal to a specified string.

string (optional) hostPrefix

Matches if the host name of the URL starts with a specified string.

string (optional) hostSuffix

Matches if the host name of the URL ends with a specified string.

string (optional) pathContains

Matches if the path segment of the URL contains a specified string.

string (optional) pathEquals

Matches if the path segment of the URL is equal to a specified string.

string (optional) pathPrefix

Matches if the path segment of the URL starts with a specified string.

string (optional) pathSuffix

Matches if the path segment of the URL ends with a specified string.

string (optional) queryContains

Matches if the query segment of the URL contains a specified string.

string (optional) queryEquals

Matches if the query segment of the URL is equal to a specified string.

string (optional) queryPrefix

Matches if the query segment of the URL starts with a specified string.

string (optional) querySuffix

Matches if the query segment of the URL ends with a specified string.

string (optional) urlContains

Matches if the URL (without fragment identifier) contains a specified string. Port numbers are stripped from the URL if they match the default port number.

string (optional) urlEquals

Matches if the URL (without fragment identifier) is equal to a specified string. Port numbers are stripped from the URL if they match the default port number.

string (optional) urlMatches

Matches if the URL (without fragment identifier) matches a specified regular expression. Port numbers are stripped from the URL if they match the default port number. The regular expressions use the RE2 syntax.

string (optional) originAndPathMatches

Matches if the URL without query segment and fragment identifier matches a specified regular expression. Port numbers are stripped from the URL if they match the default port number. The regular expressions use the RE2 syntax.

string (optional) urlPrefix

Matches if the URL (without fragment identifier) starts with a specified string. Port numbers are stripped from the URL if they match the default port number.

string (optional) urlSuffix

Matches if the URL (without fragment identifier) ends with a specified string. Port numbers are stripped from the URL if they match the default port number.

array of string (optional) schemes

Matches if the scheme of the URL is equal to any of the schemes specified in the array.

array of integer or array of integer (optional) ports

Matches if the port of the URL is contained in any of the specified port lists. For example [80, 443, [1000, 1200]] matches all requests on port 80, 443 and in the range 1000-1200.

array of string (optional) css

Matches if all of the CSS selectors in the array match displayed elements in a frame with the same origin as the page's main frame. All selectors in this array must be compound selectors to speed up matching. Note: Listing hundreds of CSS selectors or listing CSS selectors that match hundreds of times per page can slow down web sites.

boolean (optional) isBookmarked

Since Chrome 45.

Matches if the bookmarked state of the page is equal to the specified value. Requres the bookmarks permission.

ShowPageAction

Declarative event action that shows the extension's page action while the corresponding conditions are met. This action can be used without host permissions, but the extension must have a page action. If the extension has the activeTab permission, clicking the page action grants access to the active tab.

SetIcon

Since Chrome 39.

Declarative event action that sets the n-dip square icon for the extension's page action or browser action while the corresponding conditions are met. This action can be used without host permissions, but the extension must have a page or browser action.

Exactly one of imageData or path must be specified. Both are dictionaries mapping a number of pixels to an image representation. The image representation in imageData is an ImageData object; for example, from a canvas element, while the image representation in path is the path to an image file relative to the extension's manifest. If scale screen pixels fit into a device-independent pixel, the scale * n icon is used. If that scale is missing, another image is resized to the required size.

properties
ImageData or object (optional) imageData

Either an ImageData object or a dictionary {size -> ImageData} representing an icon to be set. If the icon is specified as a dictionary, the image used is chosen depending on the screen's pixel density. If the number of image pixels that fit into one screen space unit equals scale, then an image with size scale * n is selected, where n is the size of the icon in the UI. At least one image must be specified. Note that details.imageData = foo is equivalent to details.imageData = {'16': foo}.

RequestContentScript

Since Chrome 38.

Declarative event action that injects a content script.

WARNING: This action is still experimental and is not supported on stable builds of Chrome.

properties
array of string (optional) css

Names of CSS files to be injected as a part of the content script.

array of string (optional) js

Names of JavaScript files to be injected as a part of the content script.

boolean (optional) allFrames

Whether the content script runs in all frames of the matching page, or in only the top frame. Default is false.

boolean (optional) matchAboutBlank

Whether to insert the content script on about:blank and about:srcdoc. Default is false.

Events

onPageChanged

Provides the Declarative Event API consisting of addRules, removeRules, and getRules.

chrome.declarativeContent.onPageChanged.addRules(array of Rule rules, function callback) chrome.declarativeContent.onPageChanged.removeRules(array of string ruleIdentifiers, function callback) chrome.declarativeContent.onPageChanged.getRules(array of string ruleIdentifiers, function callback)

Supported conditions

Supported actions