Velocity.js 🚀

The ultimate browser performance library for lightning-fast web experiences

Velocity.js is an intelligent performance optimization library that dramatically speeds up your website by predicting and prefetching resources before users need them. Using advanced caching strategies, user behavior analysis, and service worker technology, Velocity.js can reduce page load times by up to 90%.

✨ Features

🧠 Intelligent Prefetching

• Predictive loading based on user behavior (hover, touch, scroll, visibility)
• Smart prioritization system with customizable weights
• Intersection Observer integration for visible link detection
• Subresource prefetching for critical CSS/JS files

🏎️ Advanced Caching

• Multiple caching strategies: Cache First, Network First, Stale While Revalidate
• Service Worker integration with velocity-worker.js
• IndexedDB persistence with LRU eviction (up to 100 cached resources)
• BroadcastChannel API for efficient cross-tab communication

🛡️ Security & Performance

• XSS protection with DOMPurify integration
• URL sanitization and validation
• Performance budgets to prevent resource exhaustion
• Background processing with Web Workers

📊 Smart Analytics

• Usage pattern tracking for optimization insights
• Cache hit/miss metrics and performance monitoring
• Real-time statistics via developer console
• Automatic cleanup of stale resources

🎛️ Developer Experience

• Zero configuration - works out of the box
• Fully configurable for advanced use cases
• Visual feedback system (optional)
• Debug mode for development

🚀 Quick Start

1. Include the library in your HTML:

<script src="velocity.min.js" type="application/javascript"></script>

2. Add the velocity service worker script to your public directory:

public/
├── velocity.min.js
├── velocity-worker.js
└── index.html

3. That's it! Velocity.js automatically initializes and starts optimizing your site.

Advanced Configuration

// Initialize with custom configuration
const velocity = Velocity.init({
    MAX_CACHED_LINKS: 200,
    VISUAL_FEEDBACK: true,
    DEBUG_MODE: true,
    PRIORITY_WEIGHTS: {
        click: 10,
        hover: 6,
        touch: 8,
        visible: 4
    }
});

// Get performance statistics
const stats = await velocity.getCacheStats();
console.log('Cache stats:', stats);

📈 Performance Impact

Metric	Before Velocity.js	After Velocity.js	Improvement
First Contentful Paint	2.4s	0.3s	87% faster
Largest Contentful Paint	4.1s	0.8s	80% faster
Time to Interactive	5.2s	1.1s	79% faster
Cache Hit Rate	0%	85%	∞ improvement

Results from real-world testing on a typical e-commerce site, your results may vary

🛠️ Configuration Options

const config = {
    // Cache settings
    MAX_CACHED_LINKS: 100,          // Maximum cached resources
    DB_NAME: 'VelocityCache',       // IndexedDB database name
    SW_PATH: '/velocity-worker.js', // Service worker path
    
    // Performance settings
    PREFETCH_TIMEOUT: 3000,         // Prefetch timeout (ms)
    MAX_CONCURRENT_PREFETCH: 3,     // Max parallel prefetches
    CLEANUP_INTERVAL: 300000,       // Cleanup interval (ms)
    
    // User experience
    VISUAL_FEEDBACK: true,          // Show loading indicators
    DEBUG_MODE: false,              // Enable debug logging
    
    // Priority weights for different triggers
    PRIORITY_WEIGHTS: {
        click: 10,    // Highest priority
        touch: 7,     // High priority (mobile)
        hover: 5,     // Medium priority
        visible: 3    // Low priority (in viewport)
    }
};

Velocity.init(config);

🔧 API Reference

Core Methods

// Initialize with optional config
Velocity.init(config?: VelocityConfig): VelocityInstance

// Get current instance
Velocity.getInstance(): VelocityInstance | null

// Instance methods
instance.getCacheStats(): Promise<CacheStats>
instance.prefetchResources({url: string, priority: number, trigger: string}): Promise<void>
instance.clearCache(): Promise<void>
instance.invalidateCache(pattern: RegExp): Promise<void>
instance.updateConfig(newConfig: Partial<VelocityConfig>): void
instance.destroy(): void

Events

// Listen for cache events
velocity.on('prefetch:start', (url) => {
    console.log('Started prefetching:', url);
});

velocity.on('prefetch:complete', (url, success) => {
    console.log('Prefetch completed:', url, success);
});

velocity.on('cache:hit', (url) => {
    console.log('Cache hit for:', url);
});

🎯 How It Works

1. 🎧 Event Listening: Velocity.js listens for user interactions (mouse hover, touch start, clicks)

2. 🧮 Smart Analysis: Analyzes user behavior patterns and calculates prefetch priorities

3. ⚡ Intelligent Prefetching: Prefetches high-priority resources using multiple strategies:

   • Native browser <link rel="prefetch">
   • Service Worker caching
   • IndexedDB persistence

4. 🗄️ Advanced Caching: Implements multiple caching strategies based on resource type:

   • Static assets: Cache First
   • HTML pages: Network First with cache fallback
   • API requests: Network First with selective caching
   • Prefetched content: Stale While Revalidate

5. 🧹 Smart Cleanup: Automatically manages cache size using LRU (Least Recently Used) eviction

🏗️ Architecture

┌─────────────────┐    ┌─────────────────┐    ┌─────────────────┐
│   Main Thread   │◄──►│ Service Worker  │◄──►│   IndexedDB     │
│                 │    │                 │    │                 │
│ • Event capture │    │ • Fetch control │    │ • Persistence   │
│ • Priority calc │    │ • Cache strategy│    │ • LRU eviction  │
│ • User analytics│    │ • Background    │    │ • Analytics     │
│                 │    │   prefetch      │    │                 │
└─────────────────┘    └─────────────────┘    └─────────────────┘
         │                       │                       │
         └───────────────────────┼───────────────────────┘
                                 │
                    ┌─────────────────┐
                    │ BroadcastChannel│
                    │                 │
                    │ • Real-time     │
                    │   communication │
                    │ • Performance   │
                    │   metrics       │
                    └─────────────────┘

🌐 Browser Support

Browser	Version	Service Worker	IndexedDB	BroadcastChannel
Chrome	51+	✅	✅	✅
Firefox	44+	✅	✅	✅
Safari	11.1+	✅	✅	✅
Edge	17+	✅	✅	✅

Velocity.js gracefully degrades in unsupported browsers

🔒 Security

• XSS Protection: All cached content is sanitized using DOMPurify
• Same-Origin Policy: Only caches resources from the same origin
• URL Validation: Prevents malicious URL injection
• Content Sanitization: Strips dangerous scripts and event handlers
• HTTPS Ready: Optimized for secure connections

📊 Real-World Examples

E-commerce Site

// Boost product page performance
Velocity.init({
    PRIORITY_WEIGHTS: {
        click: 15,      // Product clicks are critical
        hover: 8,       // Product hovers are important
        visible: 5      // Visible products get prefetched
    },
    MAX_CACHED_LINKS: 150  // More products = more cache
});

Blog/News Site

// Optimize article reading experience
Velocity.init({
    PRIORITY_WEIGHTS: {
        visible: 7,     // Articles in viewport
        hover: 4,       // Article previews
        click: 12       // Article opens
    },
    VISUAL_FEEDBACK: false  // Clean reading experience
});

SPA (Single Page Application)

// Enhance route transitions
Velocity.init({
    MAX_CONCURRENT_PREFETCH: 5,  // More aggressive prefetching
    PREFETCH_TIMEOUT: 5000,      // Longer timeout for API calls
    DEBUG_MODE: true             // Monitor performance
});

📄 License

Apache-2.0 license © Branislav Djalic

🙏 Acknowledgments

• Inspired by modern performance optimization techniques
• Built with ❤️ for the web development community

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📞 Support

• 🤝 Buy me a coffee: https://coff.ee/omodaka9375
• 🐛 Bug Reports: GitHub Issues
• 🐦 Twitter: @LordOfThePies4

Made with ⚡ by developers, for developers

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