Content React

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React Content Script Example

Shows a small overlay UI on every web page, with a React options page that moves it from right to left.

What you'll see: A small React UI injected into any web page, isolated in a Shadow DOM so site styles don't bleed through. The overlay carries an Open options button, and the options page behind it has one checkbox that moves the overlay between the right and left edge of the page, live.

How it works: A content script mounts a React + TypeScript UI inside a Shadow DOM and applies scoped styles so the host page can't bleed through. Styles flow through Tailwind.

The options page is the same stack, a React component mounted into an options_ui page bundled from src/options/. It reads the badgePosition setting with chrome.storage.sync.get on load and writes it with chrome.storage.sync.set on change. The value is right by default and left when the box is ticked. The content script reads that same key on injection and subscribes to chrome.storage.onChanged, so ticking the checkbox slides the overlay to the other edge without a page reload. The subscription is removed in the cleanup function Extension.js calls on teardown.

A content script cannot open the options page itself, chrome.runtime.openOptionsPage lives on the extension side. The Open options button sends {type: 'open-options'} to the background script, which makes the call. The manifest asks for the storage permission for the setting and nothing else.

Try it locally

npx extension@latest create my-content-react --template content-react
cd my-content-react
npm install
npm run dev

A fresh browser window opens with the extension already loaded.

Project layout

src/
├── content/
│   ├── ContentApp.tsx
│   ├── scripts.tsx
│   └── styles.css
├── images/
│   ├── chromeWindow.png
│   ├── icon.png
│   ├── react.png
│   ├── tailwind_bg.png
│   ├── tailwind.png
│   └── typescript.png
├── options/
│   ├── OptionsApp.tsx
│   ├── index.html
│   ├── scripts.tsx
│   └── styles.css
├── background.ts
└── manifest.json

Commands

Cloned this repo instead? The examples ship without npm scripts, so run Extension.js directly from the example directory. Run npm install first when the example declares dependencies.

dev

Run the extension in development mode. Target a browser with --browser:

npx extension@latest dev .                  # Chromium (default)
npx extension@latest dev . --browser=chrome
npx extension@latest dev . --browser=edge
npx extension@latest dev . --browser=firefox

build

Build for production:

npx extension@latest build .                # Chromium (default)
npx extension@latest build . --browser=firefox
npx extension@latest build . --browser=edge

preview

Preview the production build with the bundled browser:

npx extension@latest preview .

Tests

This template ships an end-to-end check (template.spec.ts) validated by the examples-repo CI on every commit.

Learn more

• Extension.js docs
• Templates index
• GitHub: extension-js/extension.js