crxjs

# CRXJS

CRXJS is a Chrome extension development tool that provides true HMR for popup, options, content scripts, and side panels. It reads your manifest to auto-generate the extension output, handles content script injection, and manages the service worker build. Under the hood it is a Vite plugin (`@crxjs/vite-plugin`).

## Current status

- **Package**: `@crxjs/vite-plugin` (v2.x stable, latest v2.4.0 as of March 2026)
- **Scaffolding**: `npm create crxjs@latest` (always use `@latest`)
- **Maintained by**: @Toumash and @FliPPeDround (since mid-2025)
- **GitHub**: github.com/crxjs/chrome-extension-tools (~4k stars)
- **Vite compatibility**: v3 through v8-beta

## Quick start

```bash
# Scaffold new project (picks framework interactively)
npm create crxjs@latest

# Or add to existing Vite project
npm install @crxjs/vite-plugin -D
```

## Vite config by framework

CRXJS is added as a Vite plugin. The setup varies slightly per framework.

### React

```typescript
// vite.config.ts
import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";
import { crx } from "@crxjs/vite-plugin";
import manifest from "./manifest.json";

export default defineConfig({
  plugins: [react(), crx({ manifest })],
});
```

Use `@vitejs/plugin-react` (not `plugin-react-swc`) for best HMR compatibility. If you must use SWC, cast the manifest:

```typescript
import { ManifestV3Export } from "@crxjs/vite-plugin";
const manifest = manifestJson as ManifestV3Export;
```

### Vue

```typescript
import vue from "@vitejs/plugin-vue";
import { crx } from "@crxjs/vite-plugin";
import manifest from "./manifest.json";

export default defineConfig({
  plugins: [vue(), crx({ manifest })],
});
```

### Svelte

```typescript
import { svelte } from "@sveltejs/vite-plugin-svelte";
import { crx } from "@crxjs/vite-plugin";
import manifest from "./manifest.json";

export default defineConfig({
  plugins: [svelte(), crx({ manifest })],
});
```

### Vanilla TypeScript

```typescript
import { crx } from "@crxjs/vite-plugin";
import manifest from "./manifest.json";

export default defineConfig({
  plugins: [crx({ manifest })],
});
```

## defineManifest — type-safe dynamic manifest

Instead of a static JSON file, use CRXJS's `defineManifest` for dynamic values and full TypeScript autocompletion:

```typescript
// manifest.ts
import { defineManifest } from "@crxjs/vite-plugin";
import pkg from "./package.json";

export default defineManifest((config) => ({
  manifest_version: 3,
  name: config.command === "serve" ? `[DEV] ${pkg.name}` : pkg.name,
  version: pkg.version,
  description: pkg.description,
  permissions: ["storage", "activeTab", "scripting"],
  action: {
    default_popup: "src/popup/index.html",
    default_icon: {
      "16": "public/icons/icon16.png",
      "48": "public/icons/icon48.png",
    },
  },
  background: {
    service_worker: "src/background/index.ts",
    type: "module",
  },
  content_scripts: [
    {
      matches: ["https://*/*"],
      js: ["src/content/index.ts"],
      css: ["src/content/styles.css"],
    },
  ],
  options_page: "src/options/index.html",
  side_panel: { default_path: "src/sidepanel/index.html" },
  icons: {
    "16": "public/icons/icon16.png",
    "48": "public/icons/icon48.png",
    "128": "public/icons/icon128.png",
  },
}));
```

Import in vite.config.ts:

```typescript
import manifest from "./manifest";
// ... crx({ manifest })
```

## Type declarations

Add to a `src/vite-env.d.ts` or `src/crxjs.d.ts`:

```typescript
/// <reference types="@crxjs/vite-plugin/client" />
```

This enables types for `?script` and `?script&module` imports.

## HMR behavior by context

| Context | HMR | How it works |
| --- | --- | --- |
| Popup | Full HMR | WebSocket-based, state preserved |
| Options page | Full HMR | Same as popup |
| Side panel | Full HMR | Same as popup |
| Content script (manifest) | True HMR | CRXJS injects loader + HMR client |
| Content script (dynamic) | True HMR | Via `?script` import |
| Service worker | Auto-reload | Changes trigger full extension reload |
| Main world scripts | No HMR | Skipped by CRXJS loader |

Content script HMR works because CRXJS generates a loader script that imports an HMR preamble, the HMR client, and your actual script — enabling real module-level HMR without full page reload. This is CRXJS's main differentiator.

## Dynamic content script imports

For content scripts injected programmatically (not in manifest), CRXJS provides special import suffixes:

```typescript
// background.ts — ?script gives you a resolved path for executeScript
import contentScript from "./content?script";

chrome.action.onClicked.addListener(async (tab) => {
  await chrome.scripting.executeScript({
    target: { tabId: tab.id! },
    files: [contentScript],
  });
});
```

For main world injection (no HMR):

```typescript
import mainWorldScript from "./inject?script&module";

await chrome.scripting.executeScript({
  target: { tabId },
  world: "MAIN",
  files: [mainWorldScript],
});
```

## CRXJS plugin options

```typescript
crx({
  manifest,
  browser: "chrome", // 'chrome' | 'firefox'
  contentScripts: {
    injectCss: true, // auto-inject CSS for content scripts
    hmrTimeout: 5000, // HMR connection timeout (ms)
  },
});
```

## Development workflow

```bash
# Start dev server (outputs to dist/ with HMR)
npm run dev

# 1. Open chrome://extensions
# 2. Enable "Developer mode"
# 3. Click "Load unpacked"
# 4. Select the dist/ directory
# 5. Edit code — popup/content scripts update instantly via HMR
# 6. Service worker changes trigger automatic extension reload
```

After loading once, subsequent `npm run dev` sessions reconnect automatically. No need to re-load the extension unless manifest.json changes.

## Production build

```bash
npm run build    # outputs to dist/
```

The dist/ directory is ready to zip and upload to Chrome Web Store:

```bash
cd dist && zip -r ../extension.zip .
```

Disable Vite's module preload to avoid CWS rejection of inline scripts:

```typescript
build: {
  modulePreload: false;
}
```

## Known issues and workarounds

### Tailwind CSS HMR in content scripts

New Tailwind classes may not trigger CSS updates in content scripts. **Workaround**: restart dev server after adding new utility classes. Improved in v2.4.0 but not fully resolved. Ensure `injectCss: true` in config.

### WebSocket connection errors (`ws://localhost:undefined/`)

**Cause**: port mismatch between dev server and HMR config. **Fix**: explicitly set both to the same value:

```typescript
server: {
  port: 5173,
  strictPort: true,
  hmr: { port: 5173 },
}
```

### "Manifest version 2 is deprecated" warning

If you see this, your manifest is being interpreted as MV2. **Fix**: ensure `"manifest_version": 3` is set.

### Content scripts not injecting on file:// URLs

Chrome requires the user to enable "Allow access to file URLs" in the extension settings at chrome://extensions. CRXJS cannot change this.

### HMR stops working after Chrome update

CRXJS's HMR relies on injecting a content script that connects to the dev server's WebSocket. Chrome security updates occasionally break this. **Fix**: update to the latest CRXJS version, which tracks Chrome changes.

## CRXJS vs alternatives

| Feature | CRXJS | WXT | Plasmo |
| --- | --- | --- | --- |
| Content script HMR | True HMR | File-based reload | Partial |
| Framework support | Any Vite framework | Any | React-focused |
| Abstraction level | Thin (Vite plugin) | Full framework | Full framework |
| Messaging helpers | None (use chrome.\* directly) | Built-in | Built-in |
| Storage wrappers | None | Built-in | Built-in |
| Cross-browser | Chrome + Firefox | Chrome + Firefox + Safari | Chrome + Firefox |
| File-based routing | No | Yes | Yes |
| Learning curve | Low (know Vite, know CRXJS) | Medium | Medium |

**Choose CRXJS when**: you want minimal abstraction over raw Chrome APIs and value content script HMR above all. CRXJS stays out of the way — no magic routing, no wrapper APIs, just your code with HMR.

**Choose WXT when**: you want conventions, built-in utilities, and cross-browser support.

**Choose Plasmo when**: you're React-focused and want the highest-level abstraction.

## Project structure (recommended)

```
my-extension/
├── src/
│   ├── background/
│   │   └── index.ts
│   ├── content/
│   │   ├── index.ts
│   │   └── styles.css
│   ├── popup/
│   │   ├── index.html        <- CRXJS resolves HTML entry points
│   │   ├── App.tsx
│   │   └── main.tsx
│   ├── options/
│   │   ├── index.html
│   │   └── main.tsx
│   ├── sidepanel/
│   │   ├── index.html
│   │   └── main.tsx
│   └── shared/
│       ├── messages.ts
│       └── storage.ts
├── public/
│   └── icons/
├── manifest.ts               <- or manifest.json
├── vite.config.ts
├── tsconfig.json
└── package.json
```

CRXJS resolves HTML files referenced in the manifest automatically. Your popup.html can use standard `<script type="module" src="./main.tsx">` and it works.

If you encounter a bug or unexpected behavior in CRXJS, open an issue at github.com/crxjs/chrome-extension-tools/issues.