SidepanelFallback

A lightweight fallback utility for Chrome Extensions to handle side panel conflicts. Provides browser-specific storage and display mode switching with a clean developer API.

Features

• 🚀 Automatic Fallback: Seamlessly switch between Chrome sidepanel and popup window
• 🌐 Cross-Browser Support: Works with Chrome, Firefox, Safari, Edge, and more
• 💾 Persistent Settings: Per-browser mode preferences with localStorage/Chrome Storage API
• 🎛️ Embeddable Settings UI: Ready-to-use settings component
• 🧪 Test Driven: 150+ test cases with 100% coverage using Jest and @t_wada TDD principles
• 📦 Zero Dependencies: Lightweight and self-contained
• 🔧 Developer Friendly: Clean API with TypeScript support
• ⚡ Modern Build: ES6+ modules with UMD fallback via Vite
• 📏 Code Quality: ESLint + Prettier for consistent code style

Quick Start

npm install sidepanel-fallback

import { SidepanelFallback } from 'sidepanel-fallback';

// Initialize
const fallback = new SidepanelFallback();
await fallback.init();

// Open panel (auto-detects best method)
await fallback.openPanel('/panel.html');

// Add settings UI
const container = document.getElementById('settings');
await fallback.withSettingsUI(container);

Why SidepanelFallback?

Chrome Extensions with sidepanel functionality face several challenges:

• Browser Compatibility: Sidepanel API is Chrome-specific
• API Availability: Not all Chrome versions support sidepanel
• User Preferences: Some users prefer popup windows
• Fallback Complexity: Manual fallback implementation is error-prone

SidepanelFallback solves these issues with a unified API that automatically handles browser detection, fallback logic, and user preferences.

Browser Support

| Browser | Sidepanel | Popup | Auto Mode | | ----------- | --------- | ----- | --------- | | Chrome 114+ | ✅ | ✅ | sidepanel | | Edge 114+ | ✅ | ✅ | sidepanel | | Firefox | ❌ | ✅ | window | | Safari | ❌ | ✅ | window |

API Overview

Core Methods

// Initialize the library
await fallback.init();

// Open a panel
const result = await fallback.openPanel('/panel.html');

// Add settings UI to container
await fallback.withSettingsUI(document.getElementById('settings'));

// Get current configuration
const settings = fallback.getCurrentSettings();

Chrome Extension Convenience API

For Chrome Extensions, we provide simplified methods:

// Setup extension configuration
await fallback.setupExtension({
  sidepanelPath: 'sidepanel.html',
  popupPath: 'popup.html'
});

// Handle action clicks with automatic mode detection
const result = await fallback.handleActionClick();

// Toggle between sidepanel and popup modes
await fallback.toggleMode();

Configuration Options

const fallback = new SidepanelFallback({
  defaultMode: 'auto', // 'auto', 'sidepanel', 'window'
  userAgent: 'custom-ua' // Override browser detection
});

Examples

Chrome Extension

// background.js
import { SidepanelFallback } from 'sidepanel-fallback';

const fallback = new SidepanelFallback();

chrome.action.onClicked.addListener(async () => {
  await fallback.init();
  const result = await fallback.openPanel('sidepanel.html');

  if (result.success) {
    console.log(`Panel opened using ${result.method}`);
  }
});

Chrome Extension with Simplified API

// background.js - Simplified API for easier development
import { SidepanelFallback } from 'sidepanel-fallback';

const fallback = new SidepanelFallback({ defaultMode: 'auto' });

// One-time setup
await fallback.setupExtension({
  sidepanelPath: 'sidepanel.html',
  popupPath: 'popup.html'
});

// Automatic mode handling
chrome.action.onClicked.addListener(async () => {
  await fallback.handleActionClick();
});

Web Application

// app.js
import { SidepanelFallback } from 'sidepanel-fallback';

const fallback = new SidepanelFallback();
await fallback.init();

document.getElementById('open-btn').onclick = () => {
  fallback.openPanel('/dashboard.html');
};

Complete Example

A production-ready Chrome Extension example is available in examples/chrome-extension/ featuring:

• Manifest V3 compatibility
• Automatic sidepanel ↔ popup fallback
• Settings UI with persistent preferences
• Shared UI components
• Performance monitoring

npm run build
# Load examples/chrome-extension/ in chrome://extensions/

Documentation

• 📖 Complete API Documentation
• 🏗️ Architecture & Design
• 🧪 Test Results & Coverage

Requirements

• Node.js: 18.18.0 or higher
• npm: 8.0.0 or higher
• Browser: Chrome 88+, Firefox 78+, Safari 14+, Edge 88+

Node.js Compatibility

Actively tested on Node.js 18.x (LTS), 20.x (LTS), and 22.x (Current).

Note: Some advanced test suites are disabled on Node.js 20/22 due to Jest compatibility issues. Core functionality remains fully supported.

Test Commands

npm test           # Run core tests
npm run test:full  # Run full test suite (Node.js 18 recommended)

Development

Setup

git clone https://github.com/touyou/sidepanel-fallback.git
cd sidepanel-fallback
npm install

Commands

npm test                    # Run tests
npm run test:coverage       # Run tests with coverage
npm run dev                 # Start development server
npm run build               # Build for production
npm run quality             # Run lint + format check
npm run quality:fix         # Fix lint + format issues

Test Coverage

• ✅ 150+ test cases with 100% pass rate
• ✅ Complete API coverage across all modules
• ✅ Cross-browser compatibility testing
• ✅ Integration & End-to-End testing
• ✅ Performance benchmarking and memory leak detection

Architecture

Built as focused, testable modules:

src/
├── index.js              # Main API
├── browserInfo.js        # Browser detection
├── modeStorage.js        # Settings persistence
├── panelLauncher.js      # Panel opening logic
└── settingsUI.js         # Settings UI component

Contributing

We welcome contributions! Please see our Contributing Guide for details.

Development Process

1. Fork the repository
2. Create a feature branch
3. Write tests first (TDD approach)
4. Implement the feature
5. Ensure all tests pass
6. Submit a pull request

License

MIT License - see LICENSE file for details.

Support

• 🐛 Report bugs
• 💡 Request features
• 📚 Documentation

Made with ❤️ by touyou