@addon-core/inject-css

A lightweight, TypeScript-ready library for injecting CSS into browser extension pages. Automatically detects Chrome Extension Manifest V2 and V3 and delegates to the appropriate API via @addon-core/browser.

Table of Contents

• Installation
• Usage
  • Injecting CSS Code
  • Injecting CSS Files
  • Updating Options
• API
• Options
• Examples
• License

Installation

npm:

npm install @addon-core/inject-css

pnpm:

pnpm add @addon-core/inject-css

yarn:

yarn add @addon-core/inject-css

Usage

import injectCss, {InjectCssOptions} from "@addon-core/inject-css";

// Initialize an injector with a target tab ID
const injector = injectCss({tabId: 123});

// Inject raw CSS code into the page
await injector.insert("body { background-color: #f0f0f0; }");

// Inject one or more CSS files (paths relative to extension)
await injector.file("styles/main.css");
await injector.file(["styles/reset.css", "styles/theme.css"]);

// Update options dynamically and reuse the injector
injector.options({frameId: true, origin: "USER"});
await injector.insert("p { color: red; }");

Injecting CSS Code

Use the insert(css: string) method to inject raw CSS code.

Injecting CSS Files

Use the file(files: string | string[]) method to inject CSS file(s).

Updating Options

Use the options(opts: Partial<InjectCssOptions>) method to merge or override options on an existing injector instance.

API

injectCss(options: InjectCssOptions): InjectCssContract

Creates a new CSS injector instance. Detects the manifest version (V2 or V3) via @addon-core/browser and delegates to the appropriate implementation.

InjectCssContract

• insert(css: string): Promise<void> — Inject raw CSS code.
• file(files: string | string[]): Promise<void> — Inject one or more CSS files.
• options(opts: Partial<InjectCssOptions>): this — Update injector options.

Options

The injector accepts the following options (passed to injectCss(options) and/or injector.options(opts)):

Option	Type	Description
tabId	number	Required. Target browser tab ID.
frameId	boolean | number | number[]	Optional. Select frames to inject into: true for all frames; number or array for specific.
matchAboutBlank	boolean	Optional. (V2 only) Include about:blank and similar subframes. Defaults to true.
runAt	'document_start' | 'document_end' | 'document_idle'	Optional. (V2 only) Injection timing, matches Chrome's runAt in insertCSS.
documentId	string | string[]	Optional. (V3 only) Document IDs for scripting targets.
origin	'AUTHOR' | 'USER'	Optional. CSS origin matching Chrome's API (cssOrigin in V2, origin in V3).

Examples

import injectCss from "@addon-core/inject-css";

// Initialize with a mix of options
const injector = injectCss({
    tabId: 123,
    frameId: [1, 2], // (V2 & V3)
    runAt: "document_end", // (V2 only)
    documentId: "main-doc-id", // (V3 only)
    origin: "AUTHOR", // 'AUTHOR' or 'USER'
});

// Inject raw CSS code
await injector.insert("body { background-color: #fafafa; }");

// Inject one or more CSS files
await injector.file(["styles/reset.css", "styles/theme.css"]);

License

MIT © Addon Stack