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webext-content-scripts

Utility functions to inject content scripts in WebExtensions, for Manifest v2 and v3.

Browsers: Chrome, Firefox, and Safari
Manifest: v2 and v3
Permissions: In manifest v3, you'll need the scripting permission
Context: They can be called from any context that has access to the chrome.tabs or chrome.scripting APIs

Sponsored by PixieBrix :tada:

Install

You can download the standalone bundle and include it in your manifest.json. Or use npm:

npm install webext-content-scripts

// This module is only offered as a ES Module
import {
	executeScript,
	insertCSS,
	injectContentScript,
	executeFunction,
	canAccessTab,
} from 'webext-content-scripts';

Usage

`executeScript`

Like chrome.tabs.executeScript but:

it works on Manifest v3
it can execute multiple scripts at once

executeScript({
	tabId: 1,
	frameId: 20,
	files: ['react.js', 'main.js'],
});

executeScript({
	tabId: 1,
	frameId: 20,
	files: [
		{file: 'react.js'},
		{code: 'console.log(42)'}, // This will fail on Manifest v3
	],
});

`insertCSS`

Like chrome.tabs.insertCSS but:

it works on Manifest v3
it can insert multiple styles at once

insertCSS({
	tabId: 1,
	frameId: 20,
	files: ['bootstrap.css', 'style.css'],
});

insertCSS({
	tabId: 1,
	frameId: 20,
	files: [
		{file: 'bootstrap.css'},
		{code: 'hmtl { color: red }'}
	],
});

`injectContentScript(targets, scripts)`

It combines executeScript and injectCSS in a single call. You can pass the entire content_script object from the manifest too, without change (even with snake_case_keys). It accepts either an object or an array of objects.

targets

This can be a tab ID, an array of tab IDs, a specific tab/frame combination, an array of such combinations:

injectContentScript(1, scripts);
injectContentScript([1, 2], scripts)
injectContentScript({tabId: 1, frameId: 0}, scripts);
injectContentScript([{tabId: 1, frameId: 0}, {tabId: 23, frameId: 98765}], scripts);

// You can also use the exported `getTabsByUrl` utility to inject by URL as well
injectContentScript(await getTabsByUrl(['https://example.com/*']), scripts);

Examples

const tabId = 42;
await injectContentScript(tabId, {
	runAt: 'document_idle',
	allFrames: true, // Default when passing frame-less tab IDs
	matchAboutBlank: true,
	js: [
		'contentscript.js'
	],
	css: [
		'style.css'
	],
})

await injectContentScript({
	tabId: 42,
	frameId: 56
}, [
	{
		js: [
			'jquery.js',
			'contentscript.js'
		],
		css: [
			'bootstrap.css',
			'style.css'
		],
	},
	{
	runAt: 'document_start',
		css: [
			'more-styles.css'
		],
	}
])

const tabId = 42;
const scripts = browser.runtime.getManifest().content_scripts;
// `matches`, `exclude_matches`, etc are ignored, so you can inject them on any host that you have permission to
await injectContentScript(tabId, scripts);

`executeFunction(tabId, function, ...arguments)`

`executeFunction({tabId, frameId}, function, ...arguments)`

Like chrome.tabs.executeScript, except that it accepts a raw function to be executed in the chosen tab.

const tabId = 10;

const tabUrl = await executeFunction(tabId, () => {
	alert('This code is run as a content script');
	return location.href;
});

console.log(tabUrl);

Note: The function must be self-contained because it will be serialized.

const tabId = 10;
const catsAndDogs = 'cute';

await executeFunction(tabId, () => {
	console.log(catsAndDogs); // ERROR: catsAndDogs will be undeclared and will throw an error
});

you must pass it as arguments:

const tabId = 10;
const catsAndDogs = 'cute';

await executeFunction(tabId, (localCatsAndDogs) => {
	console.log(localCatsAndDogs); // It logs "cute"
}, catsAndDogs); // Argument

`canAccessTab(tabId)`

`canAccessTab({tabId, frameId})`

Checks whether the extension has access to a specific tab or frame (i.e. content scripts are allowed to run), either via activeTab permission or regular host permissions.

const tabId = 42;
const access = await canAccessTab(tabId);
if (access) {
	console.log('We can access this tab');
	chrome.tabs.executeScript(tabId, {file: 'my-script.js'});
} else {
	console.warn('We have no access to the tab');
}

const access = await canAccessTab({
	tabId: 42,
	frameId: 56,
});
if (access) {
	console.log('We can access this frame');
	chrome.tabs.executeScript(42, {file: 'my-script.js', frameId: 56});
} else {
	console.warn('We have no access to the frame');
}

`isScriptableUrl(url)`

Browsers block access to some URLs for security reasons. This function will check whether a passed URL is blocked. Permissions and the manifest are not checked, this function is completely static. It will also returns false for any URL that doesn't start with http.

More info may be found on:

const url = 'https://addons.mozilla.org/en-US/firefox/addon/ghosttext/';
if (isScriptableUrl(url)) {
	console.log('I can inject content script to this page if permitted');
} else {
	console.log('Content scripts are never allowed on this page');
}

webext-tools - Utility functions for Web Extensions.
webext-permission-toggle - Browser-action context menu to request permission for the current tab.
webext-permissions - Get any optional permissions that users have granted you.
webext-dynamic-content-scripts - Automatically registers your content_scripts on domains added via permission.request
More…