exercises

/**
 * 19.3 Intersection Observer - Exercises
 *
 * Practice implementing IntersectionObserver patterns
 */

// ============================================
// EXERCISE 1: Advanced Lazy Loader
// ============================================

/**
 * Create an advanced lazy loader that:
 * - Loads images, videos, and iframes
 * - Shows loading placeholders
 * - Handles load errors gracefully
 * - Supports priority loading
 *
 * Requirements:
 * - Different rootMargin for high/low priority
 * - Retry failed loads
 * - Emit events for load states
 */

class AdvancedLazyLoader {
  // Your implementation here
}

/*
// SOLUTION:
class AdvancedLazyLoader {
    constructor(options = {}) {
        this.options = {
            highPriorityMargin: options.highPriorityMargin || '200px',
            lowPriorityMargin: options.lowPriorityMargin || '50px',
            retryAttempts: options.retryAttempts || 3,
            retryDelay: options.retryDelay || 1000
        };
        
        this.loadingItems = new Map();
        this.listeners = new Map();
        
        // High priority observer (larger margin)
        this.highPriorityObserver = new IntersectionObserver(
            (entries) => this.handleIntersection(entries, 'high'),
            { rootMargin: this.options.highPriorityMargin, threshold: 0 }
        );
        
        // Low priority observer
        this.lowPriorityObserver = new IntersectionObserver(
            (entries) => this.handleIntersection(entries, 'low'),
            { rootMargin: this.options.lowPriorityMargin, threshold: 0 }
        );
    }
    
    handleIntersection(entries, priority) {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                this.loadElement(entry.target, priority);
                this.getObserver(priority).unobserve(entry.target);
            }
        });
    }
    
    getObserver(priority) {
        return priority === 'high' ? 
            this.highPriorityObserver : 
            this.lowPriorityObserver;
    }
    
    observe(element, priority = 'low') {
        const type = this.getElementType(element);
        if (!type) return;
        
        element.dataset.lazyType = type;
        element.classList.add('lazy', 'lazy-pending');
        
        this.getObserver(priority).observe(element);
        this.emit('queued', { element, type, priority });
    }
    
    getElementType(element) {
        const tagName = element.tagName.toLowerCase();
        if (tagName === 'img' && element.dataset.src) return 'image';
        if (tagName === 'video' && element.dataset.src) return 'video';
        if (tagName === 'iframe' && element.dataset.src) return 'iframe';
        if (element.dataset.backgroundImage) return 'background';
        return null;
    }
    
    async loadElement(element, priority) {
        const type = element.dataset.lazyType;
        const src = element.dataset.src || element.dataset.backgroundImage;
        
        element.classList.remove('lazy-pending');
        element.classList.add('lazy-loading');
        this.emit('loading', { element, type, src });
        
        let attempts = 0;
        let success = false;
        
        while (attempts < this.options.retryAttempts && !success) {
            attempts++;
            
            try {
                await this.load(element, type, src);
                success = true;
                
                element.classList.remove('lazy-loading');
                element.classList.add('lazy-loaded');
                this.emit('loaded', { element, type, src, attempts });
                
            } catch (error) {
                if (attempts < this.options.retryAttempts) {
                    await this.delay(this.options.retryDelay * attempts);
                } else {
                    element.classList.remove('lazy-loading');
                    element.classList.add('lazy-error');
                    this.emit('error', { element, type, src, error, attempts });
                }
            }
        }
    }
    
    load(element, type, src) {
        return new Promise((resolve, reject) => {
            switch (type) {
                case 'image':
                    const img = new Image();
                    img.onload = () => {
                        element.src = src;
                        if (element.dataset.srcset) {
                            element.srcset = element.dataset.srcset;
                        }
                        resolve();
                    };
                    img.onerror = reject;
                    img.src = src;
                    break;
                    
                case 'video':
                    element.src = src;
                    element.onloadeddata = resolve;
                    element.onerror = reject;
                    element.load();
                    break;
                    
                case 'iframe':
                    element.onload = resolve;
                    element.onerror = reject;
                    element.src = src;
                    break;
                    
                case 'background':
                    const bgImg = new Image();
                    bgImg.onload = () => {
                        element.style.backgroundImage = `url(${src})`;
                        resolve();
                    };
                    bgImg.onerror = reject;
                    bgImg.src = src;
                    break;
                    
                default:
                    reject(new Error(`Unknown type: ${type}`));
            }
        });
    }
    
    delay(ms) {
        return new Promise(resolve => setTimeout(resolve, ms));
    }
    
    on(event, callback) {
        if (!this.listeners.has(event)) {
            this.listeners.set(event, []);
        }
        this.listeners.get(event).push(callback);
        return this;
    }
    
    emit(event, data) {
        const listeners = this.listeners.get(event) || [];
        listeners.forEach(cb => cb(data));
    }
    
    disconnect() {
        this.highPriorityObserver.disconnect();
        this.lowPriorityObserver.disconnect();
    }
}
*/

// ============================================
// EXERCISE 2: Section Navigator
// ============================================

/**
 * Create a section navigator that:
 * - Tracks which section is currently in view
 * - Updates navigation highlighting
 * - Supports smooth scrolling to sections
 *
 * Requirements:
 * - Handle multiple sections visible
 * - Emit section change events
 * - Track scroll direction
 */

class SectionNavigator {
  // Your implementation here
}

/*
// SOLUTION:
class SectionNavigator {
    constructor(options = {}) {
        this.options = {
            sectionSelector: options.sectionSelector || 'section[id]',
            navSelector: options.navSelector || 'nav a',
            activeClass: options.activeClass || 'active',
            offset: options.offset || 100,
            smoothScroll: options.smoothScroll !== false
        };
        
        this.sections = [];
        this.currentSection = null;
        this.lastScrollTop = 0;
        this.scrollDirection = null;
        this.listeners = new Map();
        
        this.init();
    }
    
    init() {
        // Get all sections
        this.sections = Array.from(
            document.querySelectorAll(this.options.sectionSelector)
        ).map(section => ({
            id: section.id,
            element: section
        }));
        
        // Create observer
        this.observer = new IntersectionObserver(
            this.handleIntersection.bind(this),
            {
                rootMargin: `-${this.options.offset}px 0px -50% 0px`,
                threshold: 0
            }
        );
        
        // Observe all sections
        this.sections.forEach(({ element }) => {
            this.observer.observe(element);
        });
        
        // Setup nav click handlers
        this.setupNavigation();
        
        // Track scroll direction
        this.trackScrollDirection();
    }
    
    handleIntersection(entries) {
        // Find the most visible section
        const visibleSections = [];
        
        entries.forEach(entry => {
            const section = this.sections.find(s => s.element === entry.target);
            if (section) {
                section.isIntersecting = entry.isIntersecting;
                section.intersectionRatio = entry.intersectionRatio;
            }
        });
        
        // Get currently intersecting sections
        this.sections.forEach(section => {
            if (section.isIntersecting) {
                visibleSections.push(section);
            }
        });
        
        if (visibleSections.length > 0) {
            // Choose based on scroll direction
            let newSection;
            if (this.scrollDirection === 'up') {
                newSection = visibleSections[visibleSections.length - 1];
            } else {
                newSection = visibleSections[0];
            }
            
            if (newSection.id !== this.currentSection) {
                const previousSection = this.currentSection;
                this.currentSection = newSection.id;
                
                this.updateNavigation();
                this.emit('sectionChange', {
                    current: newSection.id,
                    previous: previousSection,
                    direction: this.scrollDirection,
                    visibleSections: visibleSections.map(s => s.id)
                });
            }
        }
    }
    
    setupNavigation() {
        const navLinks = document.querySelectorAll(this.options.navSelector);
        
        navLinks.forEach(link => {
            link.addEventListener('click', (e) => {
                const href = link.getAttribute('href');
                if (href && href.startsWith('#')) {
                    e.preventDefault();
                    this.scrollTo(href.slice(1));
                }
            });
        });
    }
    
    trackScrollDirection() {
        let ticking = false;
        
        window.addEventListener('scroll', () => {
            if (!ticking) {
                requestAnimationFrame(() => {
                    const scrollTop = window.scrollY;
                    this.scrollDirection = scrollTop > this.lastScrollTop ? 'down' : 'up';
                    this.lastScrollTop = scrollTop;
                    ticking = false;
                });
                ticking = true;
            }
        }, { passive: true });
    }
    
    updateNavigation() {
        const navLinks = document.querySelectorAll(this.options.navSelector);
        
        navLinks.forEach(link => {
            const href = link.getAttribute('href');
            if (href === `#${this.currentSection}`) {
                link.classList.add(this.options.activeClass);
            } else {
                link.classList.remove(this.options.activeClass);
            }
        });
    }
    
    scrollTo(sectionId) {
        const section = this.sections.find(s => s.id === sectionId);
        if (!section) return;
        
        const top = section.element.offsetTop - this.options.offset;
        
        if (this.options.smoothScroll) {
            window.scrollTo({
                top,
                behavior: 'smooth'
            });
        } else {
            window.scrollTo(0, top);
        }
        
        this.emit('scrollTo', { sectionId });
    }
    
    on(event, callback) {
        if (!this.listeners.has(event)) {
            this.listeners.set(event, []);
        }
        this.listeners.get(event).push(callback);
        return this;
    }
    
    emit(event, data) {
        const listeners = this.listeners.get(event) || [];
        listeners.forEach(cb => cb(data));
    }
    
    getCurrentSection() {
        return this.currentSection;
    }
    
    destroy() {
        this.observer.disconnect();
    }
}
*/

// ============================================
// EXERCISE 3: Viewport Analytics
// ============================================

/**
 * Create a viewport analytics system:
 * - Track time each element is in viewport
 * - Calculate engagement metrics
 * - Generate reports
 *
 * Requirements:
 * - Track percentage viewed over time
 * - Support custom engagement thresholds
 * - Aggregate data for reporting
 */

class ViewportAnalytics {
  // Your implementation here
}

/*
// SOLUTION:
class ViewportAnalytics {
    constructor(options = {}) {
        this.options = {
            visibilityThreshold: options.visibilityThreshold || 0.5,
            engagementThreshold: options.engagementThreshold || 5000,
            sampleInterval: options.sampleInterval || 100
        };
        
        this.elements = new Map();
        this.intervals = new Map();
        
        // Create fine-grained threshold array
        const thresholds = Array.from({ length: 11 }, (_, i) => i / 10);
        
        this.observer = new IntersectionObserver(
            this.handleIntersection.bind(this),
            { threshold: thresholds }
        );
    }
    
    track(element, id = null) {
        const elementId = id || element.id || `element-${this.elements.size}`;
        
        this.elements.set(element, {
            id: elementId,
            totalViewTime: 0,
            maxVisibility: 0,
            viewCount: 0,
            engagementReached: false,
            visibilityHistory: [],
            firstSeen: null,
            lastSeen: null
        });
        
        this.observer.observe(element);
    }
    
    handleIntersection(entries) {
        const now = Date.now();
        
        entries.forEach(entry => {
            const data = this.elements.get(entry.target);
            if (!data) return;
            
            const visibility = entry.intersectionRatio;
            
            if (entry.isIntersecting) {
                // Record first seen
                if (!data.firstSeen) {
                    data.firstSeen = now;
                }
                
                // Start or continue tracking
                if (!this.intervals.has(entry.target)) {
                    data.viewCount++;
                    this.startTracking(entry.target, data);
                }
                
                // Update max visibility
                data.maxVisibility = Math.max(data.maxVisibility, visibility);
                
            } else {
                // Stop tracking when not visible
                this.stopTracking(entry.target, data, now);
            }
        });
    }
    
    startTracking(element, data) {
        const startTime = Date.now();
        
        const interval = setInterval(() => {
            data.totalViewTime += this.options.sampleInterval;
            
            // Check engagement threshold
            if (!data.engagementReached && 
                data.totalViewTime >= this.options.engagementThreshold) {
                data.engagementReached = true;
                console.log(`Engagement reached for ${data.id}`);
            }
        }, this.options.sampleInterval);
        
        this.intervals.set(element, interval);
    }
    
    stopTracking(element, data, timestamp) {
        const interval = this.intervals.get(element);
        if (interval) {
            clearInterval(interval);
            this.intervals.delete(element);
            data.lastSeen = timestamp;
        }
    }
    
    getMetrics(element) {
        const data = this.elements.get(element);
        if (!data) return null;
        
        return {
            id: data.id,
            totalViewTime: data.totalViewTime,
            maxVisibility: Math.round(data.maxVisibility * 100),
            viewCount: data.viewCount,
            engagementReached: data.engagementReached,
            averageViewDuration: data.viewCount > 0 ? 
                Math.round(data.totalViewTime / data.viewCount) : 0,
            firstSeen: data.firstSeen,
            lastSeen: data.lastSeen
        };
    }
    
    getAllMetrics() {
        const metrics = [];
        this.elements.forEach((data, element) => {
            metrics.push(this.getMetrics(element));
        });
        return metrics;
    }
    
    generateReport() {
        const metrics = this.getAllMetrics();
        
        const report = {
            timestamp: new Date().toISOString(),
            totalElements: metrics.length,
            summary: {
                averageViewTime: 0,
                engagementRate: 0,
                averageMaxVisibility: 0,
                totalViews: 0
            },
            elements: metrics
        };
        
        if (metrics.length > 0) {
            report.summary.averageViewTime = Math.round(
                metrics.reduce((sum, m) => sum + m.totalViewTime, 0) / metrics.length
            );
            report.summary.engagementRate = Math.round(
                (metrics.filter(m => m.engagementReached).length / metrics.length) * 100
            );
            report.summary.averageMaxVisibility = Math.round(
                metrics.reduce((sum, m) => sum + m.maxVisibility, 0) / metrics.length
            );
            report.summary.totalViews = metrics.reduce((sum, m) => sum + m.viewCount, 0);
        }
        
        return report;
    }
    
    reset(element = null) {
        if (element) {
            const data = this.elements.get(element);
            if (data) {
                this.stopTracking(element, data, Date.now());
                data.totalViewTime = 0;
                data.maxVisibility = 0;
                data.viewCount = 0;
                data.engagementReached = false;
            }
        } else {
            this.elements.forEach((data, el) => {
                this.stopTracking(el, data, Date.now());
            });
            this.elements.clear();
        }
    }
    
    disconnect() {
        this.intervals.forEach(interval => clearInterval(interval));
        this.intervals.clear();
        this.observer.disconnect();
    }
}
*/

// ============================================
// EXERCISE 4: Reveal Animation Manager
// ============================================

/**
 * Create a reveal animation manager:
 * - Support multiple animation types
 * - Stagger animations for lists
 * - Handle animation sequences
 *
 * Requirements:
 * - Configure animation per element
 * - Support direction-aware animations
 * - Clean up after animations complete
 */

class RevealAnimationManager {
  // Your implementation here
}

/*
// SOLUTION:
class RevealAnimationManager {
    constructor(options = {}) {
        this.options = {
            rootMargin: options.rootMargin || '0px 0px -10% 0px',
            threshold: options.threshold || 0.1,
            defaultAnimation: options.defaultAnimation || 'fadeInUp',
            defaultDuration: options.defaultDuration || 600,
            defaultDelay: options.defaultDelay || 0,
            staggerDelay: options.staggerDelay || 100
        };
        
        this.animations = {
            fadeIn: { opacity: [0, 1] },
            fadeInUp: { opacity: [0, 1], transform: ['translateY(30px)', 'translateY(0)'] },
            fadeInDown: { opacity: [0, 1], transform: ['translateY(-30px)', 'translateY(0)'] },
            fadeInLeft: { opacity: [0, 1], transform: ['translateX(-30px)', 'translateX(0)'] },
            fadeInRight: { opacity: [0, 1], transform: ['translateX(30px)', 'translateX(0)'] },
            scaleIn: { opacity: [0, 1], transform: ['scale(0.8)', 'scale(1)'] },
            slideInUp: { transform: ['translateY(100%)', 'translateY(0)'] },
            rotateIn: { opacity: [0, 1], transform: ['rotate(-10deg)', 'rotate(0)'] }
        };
        
        this.groups = new Map();
        
        this.observer = new IntersectionObserver(
            this.handleIntersection.bind(this),
            {
                rootMargin: this.options.rootMargin,
                threshold: this.options.threshold
            }
        );
    }
    
    register(element, options = {}) {
        const config = {
            animation: options.animation || element.dataset.animation || this.options.defaultAnimation,
            duration: parseInt(options.duration || element.dataset.duration) || this.options.defaultDuration,
            delay: parseInt(options.delay || element.dataset.delay) || this.options.defaultDelay,
            group: options.group || element.dataset.group || null,
            once: options.once !== false && element.dataset.once !== 'false'
        };
        
        element._revealConfig = config;
        
        // Set initial state
        this.setInitialState(element, config);
        
        // Track groups for staggering
        if (config.group) {
            if (!this.groups.has(config.group)) {
                this.groups.set(config.group, []);
            }
            this.groups.get(config.group).push(element);
        }
        
        this.observer.observe(element);
    }
    
    setInitialState(element, config) {
        const animation = this.animations[config.animation];
        if (!animation) return;
        
        element.style.opacity = '0';
        element.style.visibility = 'hidden';
    }
    
    handleIntersection(entries) {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                const config = entry.target._revealConfig;
                
                if (config.group) {
                    this.animateGroup(config.group);
                } else {
                    this.animateElement(entry.target, config);
                }
                
                if (config.once) {
                    this.observer.unobserve(entry.target);
                }
            }
        });
    }
    
    animateElement(element, config) {
        const animation = this.animations[config.animation];
        if (!animation) return;
        
        element.style.visibility = 'visible';
        
        const keyframes = Object.entries(animation).reduce((acc, [prop, values]) => {
            if (!acc[0]) {
                acc[0] = {};
                acc[1] = {};
            }
            acc[0][prop] = values[0];
            acc[1][prop] = values[1];
            return acc;
        }, []);
        
        const animationInstance = element.animate(keyframes, {
            duration: config.duration,
            delay: config.delay,
            easing: 'cubic-bezier(0.4, 0, 0.2, 1)',
            fill: 'forwards'
        });
        
        animationInstance.onfinish = () => {
            // Clean up inline styles
            element.style.opacity = '';
            element.style.transform = '';
            element.style.visibility = '';
            element.classList.add('revealed');
        };
    }
    
    animateGroup(groupId) {
        const elements = this.groups.get(groupId);
        if (!elements) return;
        
        // Filter to only visible elements that haven't been animated
        const toAnimate = elements.filter(el => 
            !el.classList.contains('revealed') && 
            el.style.visibility !== 'visible'
        );
        
        toAnimate.forEach((element, index) => {
            const config = { ...element._revealConfig };
            config.delay += index * this.options.staggerDelay;
            this.animateElement(element, config);
        });
    }
    
    addAnimation(name, keyframes) {
        this.animations[name] = keyframes;
    }
    
    reset(element = null) {
        if (element) {
            element.classList.remove('revealed');
            this.setInitialState(element, element._revealConfig);
            this.observer.observe(element);
        } else {
            document.querySelectorAll('.revealed').forEach(el => {
                this.reset(el);
            });
        }
    }
    
    disconnect() {
        this.observer.disconnect();
        this.groups.clear();
    }
}
*/

// ============================================
// EXERCISE 5: Smart Prefetcher
// ============================================

/**
 * Create a smart content prefetcher:
 * - Prefetch links when they're about to enter viewport
 * - Prioritize based on link importance
 * - Limit concurrent prefetches
 *
 * Requirements:
 * - Use IntersectionObserver for detection
 * - Respect browser's network conditions
 * - Cancel prefetches when navigating away
 */

class SmartPrefetcher {
  // Your implementation here
}

/*
// SOLUTION:
class SmartPrefetcher {
    constructor(options = {}) {
        this.options = {
            rootMargin: options.rootMargin || '200px',
            maxConcurrent: options.maxConcurrent || 3,
            prefetchTimeout: options.prefetchTimeout || 10000,
            ignorePaths: options.ignorePaths || ['/logout', '/api/']
        };
        
        this.prefetched = new Set();
        this.pending = new Map();
        this.queue = [];
        this.activeCount = 0;
        
        this.observer = new IntersectionObserver(
            this.handleIntersection.bind(this),
            {
                rootMargin: this.options.rootMargin,
                threshold: 0
            }
        );
        
        // Listen for navigation to cancel prefetches
        window.addEventListener('beforeunload', () => this.cancelAll());
    }
    
    observe(links = null) {
        const linkElements = links || document.querySelectorAll('a[href]');
        
        linkElements.forEach(link => {
            const href = link.getAttribute('href');
            
            // Only prefetch valid same-origin links
            if (this.shouldPrefetch(href)) {
                link._prefetchPriority = this.calculatePriority(link);
                this.observer.observe(link);
            }
        });
    }
    
    shouldPrefetch(href) {
        if (!href) return false;
        if (href.startsWith('#')) return false;
        if (href.startsWith('javascript:')) return false;
        if (this.prefetched.has(href)) return false;
        
        // Check ignored paths
        for (const path of this.options.ignorePaths) {
            if (href.includes(path)) return false;
        }
        
        // Check if same origin
        try {
            const url = new URL(href, window.location.origin);
            return url.origin === window.location.origin;
        } catch {
            return false;
        }
    }
    
    calculatePriority(link) {
        let priority = 1;
        
        // Higher priority for prominent links
        if (link.matches('nav a, header a')) priority += 2;
        if (link.matches('.cta, .primary, [data-prefetch="high"]')) priority += 3;
        if (link.matches('footer a, aside a')) priority -= 1;
        
        return priority;
    }
    
    handleIntersection(entries) {
        entries.forEach(entry => {
            if (entry.isIntersecting) {
                const href = entry.target.getAttribute('href');
                const priority = entry.target._prefetchPriority || 1;
                
                this.queuePrefetch(href, priority);
                this.observer.unobserve(entry.target);
            }
        });
    }
    
    queuePrefetch(href, priority) {
        if (this.prefetched.has(href) || this.pending.has(href)) return;
        
        // Check network conditions
        if (!this.canPrefetch()) {
            console.log('Skipping prefetch due to network conditions');
            return;
        }
        
        this.queue.push({ href, priority });
        this.queue.sort((a, b) => b.priority - a.priority);
        
        this.processQueue();
    }
    
    canPrefetch() {
        // Check if save-data is enabled
        if ('connection' in navigator) {
            const conn = navigator.connection;
            if (conn.saveData) return false;
            if (conn.effectiveType === '2g' || conn.effectiveType === 'slow-2g') return false;
        }
        return true;
    }
    
    processQueue() {
        while (this.queue.length > 0 && this.activeCount < this.options.maxConcurrent) {
            const { href } = this.queue.shift();
            this.prefetch(href);
        }
    }
    
    async prefetch(href) {
        if (this.prefetched.has(href) || this.pending.has(href)) return;
        
        this.activeCount++;
        
        const controller = new AbortController();
        const timeoutId = setTimeout(() => controller.abort(), this.options.prefetchTimeout);
        
        this.pending.set(href, { controller, timeoutId });
        
        try {
            // Use link prefetch if supported
            if (this.supportsPrefetch()) {
                const link = document.createElement('link');
                link.rel = 'prefetch';
                link.href = href;
                document.head.appendChild(link);
                
                await new Promise((resolve, reject) => {
                    link.onload = resolve;
                    link.onerror = reject;
                    setTimeout(resolve, 100); // Fallback
                });
            } else {
                // Fallback to fetch
                await fetch(href, {
                    method: 'GET',
                    credentials: 'same-origin',
                    signal: controller.signal,
                    headers: {
                        'Purpose': 'prefetch'
                    }
                });
            }
            
            this.prefetched.add(href);
            console.log('Prefetched:', href);
            
        } catch (error) {
            if (error.name !== 'AbortError') {
                console.warn('Prefetch failed:', href, error.message);
            }
        } finally {
            clearTimeout(timeoutId);
            this.pending.delete(href);
            this.activeCount--;
            this.processQueue();
        }
    }
    
    supportsPrefetch() {
        const link = document.createElement('link');
        return link.relList && link.relList.supports && link.relList.supports('prefetch');
    }
    
    cancelAll() {
        this.queue = [];
        
        this.pending.forEach(({ controller, timeoutId }) => {
            clearTimeout(timeoutId);
            controller.abort();
        });
        
        this.pending.clear();
    }
    
    getStats() {
        return {
            prefetched: this.prefetched.size,
            pending: this.pending.size,
            queued: this.queue.length
        };
    }
    
    disconnect() {
        this.cancelAll();
        this.observer.disconnect();
    }
}
*/

// ============================================
// TEST UTILITIES
// ============================================

console.log('=== IntersectionObserver Exercises ===');
console.log('');
console.log('Exercises:');
console.log('1. AdvancedLazyLoader - Multi-type lazy loading with retry');
console.log('2. SectionNavigator - Scroll-aware navigation');
console.log('3. ViewportAnalytics - Track viewport metrics');
console.log('4. RevealAnimationManager - Scroll-triggered animations');
console.log('5. SmartPrefetcher - Intelligent link prefetching');
console.log('');
console.log('These exercises require a browser environment.');
console.log('Uncomment solutions to see implementations.');

// Export for browser use
if (typeof module !== 'undefined' && module.exports) {
  module.exports = {
    AdvancedLazyLoader,
    SectionNavigator,
    ViewportAnalytics,
    RevealAnimationManager,
    SmartPrefetcher,
  };
}