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.

Permissions

declarativeContent

Concepts and usage

The Declarative Content API lets you enable your extension's action depending on the URL of a web page, or if a CSS selector matches an element on the page, without needing to add host permissions or inject a content script.

Use the activeTab permission to interact with a page after the user clicks on the extension's action.

Rules

Rules consists of conditions and actions. If any of the conditions is fulfilled, all actions are executed. The actions are setIcon() and showAction().

The PageStateMatcher matches web pages if and only if all listed criteria are met. It can match a page url, a css compound selector or the bookmarked state of a page. The following rule enables the extension's action on Google pages when a password field is present:

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

To also enable the extension's action for Google sites with a video, you can add a second condition, as each condition is sufficient to trigger all specified actions:

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

The onPageChanged event tests whether any rule has at least one fulfilled condition and executes the actions. Rules persist across browsing sessions; therefore, during extension installation time you should first use removeRules to clear previously installed rules and then use addRules to register new ones.

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

With the activeTab permission, your extension won't display any permission warnings and when the user clicks the extension action, it will only run on relevant pages.

Page URL matching

The PageStateMatcher.pageurl matches when the URL criteria are fulfilled. The most common criteria are a concatenation of either host, path, or URL, followed by Contains, Equals, Prefix, or Suffix. The following table contains a few examples:

Criteria	Matches
`{ hostSuffix: 'google.com' }`	All Google URLs
`{ pathPrefix: '/docs/extensions'` }	Extension docs URLs
`{ urlContains: 'developer.chrome.com'` }	All chrome developers docs URLs

All criteria are case sensitive. For a complete list of criteria, see UrlFilter.

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)
`a`	`div p`
`iframe.special[src^='http']`	`p>span.highlight`
`ns\|*`	`p + ol`
`#abcd:checked`	`p::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.

Types

ImageDataType

See https://developer.mozilla.org/en-US/docs/Web/API/ImageData.

Type

ImageData

PageStateMatcher

Matches the state of a web page based on various criteria.

Properties

constructor

void

The constructor function looks like:
```
(arg: PageStateMatcher) => {...}
```
- arg
  
  PageStateMatcher
- returns
  PageStateMatcher
css

string[] optional

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.
isBookmarked

boolean optional

Chrome 45+

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

UrlFilter optional

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

RequestContentScript

Declarative event action that injects a content script.

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

Properties

constructor

void

The constructor function looks like:
```
(arg: RequestContentScript) => {...}
```
- arg
  
  RequestContentScript
- returns
  RequestContentScript
allFrames

boolean optional

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

string[] optional

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

string[] optional

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

boolean optional

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

SetIcon

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

constructor

void

The constructor function looks like:
```
(arg: SetIcon) => {...}
```
- arg
  
  SetIcon
- returns
  SetIcon
imageData

ImageData | object optional

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}.

ShowAction

Chrome 97+

A declarative event action that sets the extension's toolbar action to an enabled state while the corresponding conditions are met. This action can be used without host permissions. If the extension has the activeTab permission, clicking the page action grants access to the active tab.

On pages where the conditions are not met the extension's toolbar action will be grey-scale, and clicking it will open the context menu, instead of triggering the action.

Properties

constructor

void

The constructor function looks like:
```
(arg: ShowAction) => {...}
```
- arg
  
  ShowAction
- returns
  ShowAction

ShowPageAction

Deprecated since Chrome 97

Please use declarativeContent.ShowAction.

A declarative event action that sets the extension's page action to an enabled state 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.

On pages where the conditions are not met the extension's toolbar action will be grey-scale, and clicking it will open the context menu, instead of triggering the action.

Properties

constructor

void

The constructor function looks like:
```
(arg: ShowPageAction) => {...}
```
- arg
  
  ShowPageAction
- returns
  ShowPageAction

Events

onPageChanged

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

Conditions

PageStateMatcher

Actions