前端取经路——性能优化：唐僧的九道心经

大家好，我是老十三，一名前端开发工程师。性能优化如同唐僧的九道心经，是前端修行的精髓所在。在本文中，我将为你揭示从网络传输到渲染优化的九大关键技术，涵盖HTTP协议、资源加载策略、缓存控制等核心难题。通过这些实战技巧，你将能打造出如行云流水般顺滑的用户体验，让你的应用脱胎换骨，达到性能优化的"大乘境界"。

工程化之道修行完毕，我们继续西行，迎来前端取经第六关——性能优化。唐僧虽不像孙悟空那般神通广大，但他的九道心经却是取经团队的精神支柱。同样，前端性能优化虽不如框架技术那般光鲜，却是用户体验的根本保障，值得每位前端修行者深入探索。

🚀 第一难：网络优化 - HTTP/2与HTTP/3的"缩地术"

问题：为什么我的网站在弱网环境下体验差？如何利用现代网络协议提升加载速度？

深度技术：

网络传输是前端性能的第一道关卡，而HTTP协议的演进极大改变了资源加载效率。从HTTP/1.1到HTTP/2再到HTTP/3，每一代协议都带来了性能突破。

HTTP/2引入了多路复用、头部压缩、服务器推送等特性，彻底改变了我们对"减少HTTP请求"的传统优化思路；而基于UDP的HTTP/3（QUIC）进一步解决了队头阻塞问题，提供更可靠的弱网环境表现。理解这些协议的核心机制，才能设计出真正高效的前端资源加载策略。

代码示例：

// 1. HTTP/2服务器推送配置
// Nginx配置示例
server {listen 443 ssl http2;server_name example.com;ssl_certificate     /path/to/cert.pem;ssl_certificate_key /path/to/key.pem;// HTTP/2服务器推送location / {root /var/www/html;http2_push /styles/main.css;http2_push /scripts/main.js;http2_push /images/logo.png;}
}// 2. Link预加载标头（替代服务器推送）
// Express.js中间件示例
app.get('/', (req, res) => {// 使用Link头预告关键资源res.set('Link', ['</styles/main.css>; rel=preload; as=style','</scripts/main.js>; rel=preload; as=script','</fonts/awesome.woff2>; rel=preload; as=font; crossorigin'].join(', '));res.render('index');
});// 3. 域名分片（HTTP/1.1时代的优化，HTTP/2下反而有害）
// bad.js - HTTP/2下不推荐
function loadImagesFromMultipleDomains() {const domains = ['assets1.example.com','assets2.example.com','assets3.example.com'];return images.map((image, index) => {const domain = domains[index % domains.length];return `https://${domain}/${image.path}`;});
}// good.js - HTTP/2下推荐
function loadImagesFromSingleDomain() {// 使用单一域名，利用HTTP/2多路复用return images.map(image => `https://assets.example.com/${image.path}`);
}// 4. 资源合并（HTTP/1.1时代的优化，HTTP/2下需重新评估）
// webpack.config.js
module.exports = {// HTTP/1.1环境: 推荐合并文件减少请求数// HTTP/2环境: 适度拆分，利用并行加载optimization: {splitChunks: {chunks: 'all',maxInitialRequests: 10, // HTTP/2下可以设置更高maxAsyncRequests: 10,cacheGroups: {vendor: {test: /[\\/]node_modules[\\/]/,name: 'vendors',chunks: 'all'}}}}
};// 5. 使用CDN加速
// index.html中引用CDN资源
<script src="https://cdn.example.com/libraries/react.production.min.js"></script>// 配置CDN回源
// 使用源站防护，控制CDN回源流量
const config = {cdnDomain: 'cdn.example.com',// 避免直接访问源站preventDirectAccess: process.env.NODE_ENV === 'production',generateUrl(path) {return `https://${this.cdnDomain}/${path}`;}
};// 6. 分析并优化第三方资源
// 第三方资源审计脚本
function auditThirdPartyResources() {const resources = performance.getEntriesByType('resource');// 按域名分组统计const domainStats = {};resources.forEach(resource => {const url = new URL(resource.name);const domain = url.hostname;if (!domainStats[domain]) {domainStats[domain] = {count: 0,totalSize: 0,resources: []};}domainStats[domain].count++;domainStats[domain].totalSize += resource.encodedBodySize || 0;domainStats[domain].resources.push({url: resource.name,size: resource.encodedBodySize || 0,duration: resource.duration,initiatorType: resource.initiatorType});});console.table(Object.entries(domainStats).map(([domain, stats]) => ({Domain: domain,Requests: stats.count,'Total Size (KB)': (stats.totalSize / 1024).toFixed(2),'Is Third Party': !domain.includes(window.location.hostname)})));
}// 7. 实现HTTP/3检测和回退
function detectHttp3Support() {return new Promise(resolve => {const img = new Image();const start = performance.now();let http3Supported = false;// 尝试通过HTTP/3加载1x1像素图片img.src = 'https://http3-test.example.com/pixel.png?cachebust=' + Math.random();// 如果加载时间短，可能支持HTTP/3img.onload = () => {const loadTime = performance.now() - start;http3Supported = loadTime < 50; // 假设50ms是阈值resolve(http3Supported);};img.onerror = () => {resolve(false);};// 如果超过1秒还没加载完，认为不支持setTimeout(() => {if (!http3Supported) {resolve(false);}}, 1000);});
}

📊 第二难：加载策略 - 资源优先级的"火眼金睛"

问题：加载顺序如何影响用户体验？如何只加载当前页面真正需要的资源？

深度技术：

网页加载是一场与时间赛跑的过程，而资源优先级策略决定了这场比赛的成败。关键在于理解渲染路径和资源加载对页面展示的影响，确保首屏关键内容最先加载完成。

现代浏览器提供了多种资源提示（Resource Hints）机制：preload（预加载）、prefetch（预获取）、preconnect（预连接）等，正确使用这些技术可以精确控制资源加载顺序和时机。同时，按需加载和代码分割（Code Splitting）策略也是优化大型应用加载性能的关键手段。

代码示例：

<!-- 1. 资源提示示例 -->
<!-- Preload - 当前页面必需的高优先级资源 -->
<link rel="preload" href="/fonts/awesome.woff2" as="font" type="font/woff2" crossorigin>
<link rel="preload" href="/critical.css" as="style">
<link rel="preload" href="/hero-image.jpg" as="image" media="(min-width: 600px)"><!-- Prefetch - 可能在未来页面用到的资源 -->
<link rel="prefetch" href="/next-page.js">
<link rel="prefetch" href="/articles/popular.json"><!-- Preconnect - 提前建立连接 -->
<link rel="preconnect" href="https://api.example.com">
<link rel="dns-prefetch" href="https://analytics.example.com"><!-- 预渲染下一页 -->
<link rel="prerender" href="https://example.com/next-page"><!-- 2. 关键CSS内联 -->
<style>/* 首屏关键样式内联 */.hero {height: 100vh;display: flex;align-items: center;justify-content: center;background-color: #f0f0f0;}.hero-title {font-size: 2.5rem;font-weight: bold;color: #333;}/* 其他首屏必需样式... */
</style><!-- 异步加载非关键CSS -->
<link rel="preload" href="/main.css" as="style" onload="this.onload=null;this.rel='stylesheet'">
<noscript><link rel="stylesheet" href="/main.css"></noscript><!-- 3. 脚本加载策略 -->
<!-- 延迟执行，不阻塞解析 -->
<script src="/analytics.js" defer></script><!-- 异步加载，不阻塞解析，下载完立即执行 -->
<script src="/widget.js" async></script><!-- 模块脚本，自动延迟 -->
<script type="module" src="/app.js"></script>
<script nomodule src="/app-legacy.js"></script><!-- 内联关键脚本 -->
<script>// 初始化首屏必需功能document.addEventListener('DOMContentLoaded', () => {initCriticalFeatures();});
</script><!-- 4. 图片资源策略 -->
<!-- 响应式图片 -->
<picture><source srcset="/hero-large.webp 1200w, /hero-medium.webp 800w" type="image/webp"><source srcset="/hero-large.jpg 1200w, /hero-medium.jpg 800w" type="image/jpeg"> <img src="/hero-fallback.jpg" alt="Hero image" loading="eager" width="1200" height="600">
</picture><!-- 延迟加载非首屏图片 -->
<img src="placeholder.svg" data-src="product.jpg" alt="Product" loading="lazy" class="lazyload"><!-- 5. JavaScript实现资源优先级管理 -->
<script>
// 动态插入预加载
function preloadCriticalAssets() {const assets = [{ href: '/app.js', as: 'script' },{ href: '/logo.svg', as: 'image' }];assets.forEach(asset => {const link = document.createElement('link');link.rel = 'preload';link.href = asset.href;link.as = asset.as;if (asset.as === 'font') {link.crossOrigin = 'anonymous';}document.head.appendChild(link);});
}// 根据路由预测和预加载
function predictNextNavigation() {// 分析用户行为，预测下一个导航目标const links = Array.from(document.querySelectorAll('a'));const visibleLinks = links.filter(link => {const rect = link.getBoundingClientRect();return (rect.top >= 0 &&rect.left >= 0 &&rect.bottom <= window.innerHeight &&rect.right <= window.innerWidth);});// 为可视区域内的链接添加prefetchvisibleLinks.forEach(link => {const href = link.getAttribute('href');if (href && href.startsWith('/') && !link.dataset.prefetched) {const prefetchLink = document.createElement('link');prefetchLink.rel = 'prefetch';prefetchLink.href = href;document.head.appendChild(prefetchLink);link.dataset.prefetched = 'true';}});
}// 优先级队列实现
class ResourcePriorityQueue {constructor() {this.highPriority = [];this.mediumPriority = [];this.lowPriority = [];this.loaded = new Set();}add(resource, priority = 'medium') {if (this.loaded.has(resource.url)) return;switch(priority) {case 'high':this.highPriority.push(resource);break;case 'low':this.lowPriority.push(resource);break;default:this.mediumPriority.push(resource);}}processNext() {const resource = this.highPriority.shift() || this.mediumPriority.shift() || this.lowPriority.shift();if (!resource) return Promise.resolve();return this.loadResource(resource).then(() => {this.loaded.add(resource.url);return this.processNext();}).catch(err => {console.error(`Failed to load ${resource.url}:`, err);return this.processNext();});}loadResource(resource) {// 根据资源类型选择加载策略switch(resource.type) {case 'script':return this.loadScript(resource.url, resource.async);case 'style':return this.loadStyle(resource.url);case 'image':return this.loadImage(resource.url);default:return this.loadGeneric(resource.url);}}// 各种资源加载实现...loadScript(url, async = false) {return new Promise((resolve, reject) => {const script = document.createElement('script');script.src = url;script.async = async;script.onload = resolve;script.onerror = reject;document.head.appendChild(script);});}loadStyle(url) {return new Promise((resolve, reject) => {const link = document.createElement('link');link.rel = 'stylesheet';link.href = url;link.onload = resolve;link.onerror = reject;document.head.appendChild(link);});}// 其他加载方法...
}// 使用示例
document.addEventListener('DOMContentLoaded', () => {const queue = new ResourcePriorityQueue();// 添加各种优先级的资源queue.add({ url: '/critical.js', type: 'script' }, 'high');queue.add({ url: '/menu.js', type: 'script' }, 'medium');queue.add({ url: '/analytics.js', type: 'script' }, 'low');// 开始处理队列queue.processNext();// 视口可见性变化时处理低优先级资源document.addEventListener('visibilitychange', () => {if (document.visibilityState === 'visible') {queue.processNext();}});
});
</script>

🗄️ 第三难：缓存控制 - 浏览器存储的"八卦炉"

问题：如何合理利用浏览器缓存加速页面访问？不同缓存策略在什么场景下最有效？

深度技术：

浏览器缓存是性能优化的强大工具，正确的缓存策略可以显著减少网络请求，加速页面加载。前端缓存策略需要考虑多个层面：HTTP缓存（通过Cache-Control和ETag控制）、ServiceWorker离线缓存、以及浏览器存储API（LocalStorage、SessionStorage、IndexedDB）。

设计缓存策略的关键在于平衡缓存时效性和命中率：频繁变化的内容需要短缓存或验证缓存，而静态资源则可使用长缓存配合内容哈希。理解不同缓存机制的特点和适用场景，才能构建出最优的缓存架构。

代码示例：

// 1. HTTP缓存控制
// nginx服务器配置
server {// 长缓存静态资源（带版本号或哈希的文件）location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg)$ {expires 1y;add_header Cache-Control "public, max-age=31536000, immutable";etag off;access_log off;}// HTML文件使用验证缓存location ~* \.html$ {add_header Cache-Control "no-cache";add_header ETag ""; // 启用ETag}// API响应不缓存location /api/ {add_header Cache-Control "no-store";add_header Pragma "no-cache";}
}// Express服务器配置
app.use('/static', express.static('public', {maxAge: '1y',etag: false,lastModified: false,setHeaders: (res, path) => {if (path.includes('chunk.') || path.includes('vendor.')) {// 包含哈希的文件使用不变缓存res.setHeader('Cache-Control', 'public, max-age=31536000, immutable');}}
}));// 2. Service Worker缓存
// sw.js - Service Worker文件
const CACHE_NAME = 'app-cache-v1';
const urlsToCache = ['/','/index.html','/styles/main.css','/scripts/main.js','/images/logo.png'
];// 安装Service Worker
self.addEventListener('install', event => {event.waitUntil(caches.open(CACHE_NAME).then(cache => {console.log('Opened cache');return cache.addAll(urlsToCache);}));
});// 缓存优先，网络回退策略
self.addEventListener('fetch', event => {event.respondWith(caches.match(event.request).then(response => {// 缓存命中if (response) {return response;}// 缓存未命中，发起网络请求return fetch(event.request).then(networkResponse => {// 检查是否为有效响应if (!networkResponse || networkResponse.status !== 200 || networkResponse.type !== 'basic') {return networkResponse;}// 复制响应，因为响应流只能被读取一次const responseToCache = networkResponse.clone();caches.open(CACHE_NAME).then(cache => {// 只缓存同源资源if (new URL(event.request.url).origin === location.origin) {cache.put(event.request, responseToCache);}});return networkResponse;});}));
});// 更新Service Worker时清理旧缓存
self.addEventListener('activate', event => {const cacheWhitelist = [CACHE_NAME];event.waitUntil(caches.keys().then(cacheNames => {return Promise.all(cacheNames.map(cacheName => {if (cacheWhitelist.indexOf(cacheName) === -1) {return caches.delete(cacheName);}}));}));
});// 注册Service Worker
if ('serviceWorker' in navigator) {window.addEventListener('load', () => {navigator.serviceWorker.register('/sw.js').then(registration => {console.log('ServiceWorker registration successful with scope: ', registration.scope);}).catch(error => {console.log('ServiceWorker registration failed: ', error);});});
}// 3. 浏览器存储API
// LocalStorage - 持久化简单数据
const StorageManager = {// 设置带过期时间的缓存项setItem(key, value, expiryInMinutes = 60) {const item = {value,expiry: expiryInMinutes ? Date.now() + (expiryInMinutes * 60000) : null};localStorage.setItem(key, JSON.stringify(item));},// 获取数据，自动检查是否过期getItem(key) {const itemStr = localStorage.getItem(key);if (!itemStr) return null;try {const item = JSON.parse(itemStr);if (item.expiry && Date.now() > item.expiry) {localStorage.removeItem(key);return null;}return item.value;} catch (e) {console.error('Error parsing storage item:', e);return null;}},// 移除数据removeItem(key) {localStorage.removeItem(key);},// 清理所有过期项clearExpired() {for (let i = 0; i < localStorage.length; i++) {const key = localStorage.key(i);this.getItem(key); // 会自动检查和清理过期项}}
};// 使用示例
StorageManager.setItem('user-preferences', { theme: 'dark', fontSize: 'large' }, 1440); // 24小时过期
const preferences = StorageManager.getItem('user-preferences');// 4. IndexedDB - 存储大量结构化数据
class IndexedDBStorage {constructor(dbName, version) {this.dbName = dbName;this.version = version;this.db = null;}open() {return new Promise((resolve, reject) => {const request = indexedDB.open(this.dbName, this.version);request.onerror = () => reject(request.error);request.onsuccess = () => {this.db = request.result;resolve(this.db);};request.onupgradeneeded = (event) => {const db = event.target.result;// 创建存储对象if (!db.objectStoreNames.contains('articles')) {const store = db.createObjectStore('articles', { keyPath: 'id' });store.createIndex('by_date', 'date');}};});}// 保存文章saveArticle(article) {return new Promise((resolve, reject) => {const transaction = this.db.transaction(['articles'], 'readwrite');const store = transaction.objectStore('articles');// 添加或更新文章const request = store.put({...article,cacheDate: new Date()});request.onsuccess = () => resolve(article);request.onerror = () => reject(request.error);});}// 获取文章getArticle(id) {return new Promise((resolve, reject) => {const transaction = this.db.transaction(['articles']);const store = transaction.objectStore('articles');const request = store.get(id);request.onsuccess = () => resolve(request.result);request.onerror = () => reject(request.error);});}// 获取符合日期范围的文章getArticlesByDateRange(startDate, endDate) {return new Promise((resolve, reject) => {const transaction = this.db.transaction(['articles']);const store = transaction.objectStore('articles');const index = store.index('by_date');const range = IDBKeyRange.bound(startDate, endDate);const request = index.openCursor(range);const articles = [];request.onsuccess = (event) => {const cursor = event.target.result;if (cursor) {articles.push(cursor.value);cursor.continue();} else {resolve(articles);}};request.onerror = () => reject(request.error);});}
}// 使用示例
async function cacheArticles() {const db = new IndexedDBStorage('content-db', 1);await db.open();try {// 获取文章并缓存const response = await fetch('/api/articles');const articles = await response.json();for (const article of articles) {await db.saveArticle(article);}console.log('All articles cached successfully');} catch (error) {console.error('Error caching articles:', error);}
}// 5. 高级缓存策略实现
class CacheStrategy {constructor() {this.strategies = {cacheFirst: this.cacheFirst.bind(this),networkFirst: this.networkFirst.bind(this),staleWhileRevalidate: this.staleWhileRevalidate.bind(this)};}// 缓存优先，适用于不经常变化的资源async cacheFirst(url, cacheName) {const cache = await caches.open(cacheName);const cachedResponse = await cache.match(url);if (cachedResponse) {return cachedResponse;}const networkResponse = await fetch(url);cache.put(url, networkResponse.clone());return networkResponse;}// 网络优先，适用于经常更新的内容async networkFirst(url, cacheName, timeoutMs = 3000) {const cache = await caches.open(cacheName);try {// 设置超时，避免网络请求过长const networkPromise = fetch(url);const timeoutPromise = new Promise((_, reject) => {setTimeout(() => reject(new Error('Network timeout')), timeoutMs);});// 竞态Promise，哪个先完成用哪个const networkResponse = await Promise.race([networkPromise, timeoutPromise]);cache.put(url, networkResponse.clone());return networkResponse;} catch (error) {const cachedResponse = await cache.match(url);if (cachedResponse) {return cachedResponse;}throw error;}}// 边用缓存边更新，平衡速度和新鲜度async staleWhileRevalidate(url, cacheName) {const cache = await caches.open(cacheName);// 立即返回缓存（如果有）const cachedResponse = await cache.match(url);// 无论是否有缓存，都触发网络更新const updatePromise = fetch(url).then(networkResponse => {cache.put(url, networkResponse.clone());return networkResponse;});// 如果有缓存就返回缓存，否则等待网络请求return cachedResponse || updatePromise;}// 根据URL选择合适的策略async fetch(url, options = {}) {const { strategy = 'networkFirst', cacheName = 'default-cache' } = options;if (!this.strategies[strategy]) {throw new Error(`Unknown cache strategy: ${strategy}`);}return this.strategies[strategy](url, cacheName);}
}// 使用示例
const cacheManager = new CacheStrategy();// 对API请求使用网络优先策略
async function fetchUserData(userId) {try {const response = await cacheManager.fetch(`/api/users/${userId}`, {strategy: 'networkFirst',cacheName: 'api-cache'});return response.json();} catch (error) {console.error('Failed to fetch user data:', error);return null;}
}// 对静态资源使用缓存优先策略
async function fetchStaticContent(path) {try {const response = await cacheManager.fetch(`/static/${path}`, {strategy: 'cacheFirst',cacheName: 'static-cache'});return response;} catch (error) {console.error(`Failed to fetch static content: ${path}`, error);return null;}
}

🖼️ 第四难：图片优化 - 下一代格式的"缩骨术"

问题：如何在不影响图片质量的前提下，显著减少图片体积？现代图片格式和优化技术能带来哪些提升？

深度技术：

图片优化是前端性能优化的重要环节，现代图片格式如WebP、AVIF等提供了更好的压缩率，而响应式图片技术则能根据设备特性提供最优图片。理解图片格式特性、压缩原理和加载策略，是提升页面性能的关键。

代码示例：

// 1. 响应式图片实现
<picture><!-- WebP格式，支持时优先使用 --><sourcesrcset="/images/hero-400.webp 400w,/images/hero-800.webp 800w,/images/hero-1200.webp 1200w"type="image/webp"sizes="(max-width: 400px) 400px,(max-width: 800px) 800px,1200px"><!-- 传统格式回退 --><sourcesrcset="/images/hero-400.jpg 400w,/images/hero-800.jpg 800w,/images/hero-1200.jpg 1200w"type="image/jpeg"sizes="(max-width: 400px) 400px,(max-width: 800px) 800px,1200px"><!-- 最终回退方案 --><imgsrc="/images/hero-400.jpg"alt="Hero image"loading="eager"width="1200"height="600">
</picture>// 2. 图片懒加载实现
class LazyLoader {constructor(options = {}) {this.options = {root: null,rootMargin: '0px',threshold: 0.1,...options};this.observer = new IntersectionObserver(this.handleIntersection.bind(this),this.options);}observe(elements) {elements.forEach(element => {if (element.dataset.src) {this.observer.observe(element);}});}handleIntersection(entries) {entries.forEach(entry => {if (entry.isIntersecting) {this.loadImage(entry.target);this.observer.unobserve(entry.target);}});}loadImage(element) {const src = element.dataset.src;if (!src) return;// 创建新图片对象预加载const img = new Image();img.onload = () => {element.src = src;element.classList.add('loaded');};img.src = src;}
}// 3. 图片压缩和转换
const sharp = require('sharp');async function optimizeImage(inputPath, outputPath, options = {}) {const {width,height,quality = 80,format = 'webp'} = options;try {let pipeline = sharp(inputPath);// 调整尺寸if (width || height) {pipeline = pipeline.resize(width, height, {fit: 'inside',withoutEnlargement: true});}// 根据格式转换switch (format) {case 'webp':pipeline = pipeline.webp({ quality });break;case 'avif':pipeline = pipeline.avif({ quality });break;case 'jpeg':pipeline = pipeline.jpeg({ quality });break;default:pipeline = pipeline.webp({ quality });}await pipeline.toFile(outputPath);console.log(`Image optimized: ${outputPath}`);} catch (error) {console.error('Image optimization failed:', error);}
}// 4. 图片加载优化
class ImageLoader {constructor() {this.loadingQueue = [];this.maxConcurrent = 3;this.currentLoading = 0;}load(url, priority = 'normal') {return new Promise((resolve, reject) => {this.loadingQueue.push({url,priority,resolve,reject});this.processQueue();});}processQueue() {if (this.currentLoading >= this.maxConcurrent) return;// 按优先级排序this.loadingQueue.sort((a, b) => {const priorityOrder = { high: 0, normal: 1, low: 2 };return priorityOrder[a.priority] - priorityOrder[b.priority];});const next = this.loadingQueue.shift();if (!next) return;this.currentLoading++;const img = new Image();img.onload = () => {this.currentLoading--;next.resolve(img);this.processQueue();};img.onerror = () => {this.currentLoading--;next.reject(new Error(`Failed to load image: ${next.url}`));this.processQueue();};img.src = next.url;}
}// 5. 图片预加载策略
class ImagePreloader {constructor() {this.cache = new Map();this.loader = new ImageLoader();}preload(urls, priority = 'low') {return Promise.all(urls.map(url => {if (this.cache.has(url)) {return Promise.resolve(this.cache.get(url));}return this.loader.load(url, priority).then(img => {this.cache.set(url, img);return img;});}));}// 预测用户可能查看的图片predictNextImages(currentPath) {const predictions = {'/': ['/images/hero.webp', '/images/featured-1.webp'],'/products': ['/images/product-list.webp'],'/about': ['/images/team.webp']};return predictions[currentPath] || [];}
}// 使用示例
const preloader = new ImagePreloader();// 预加载当前页面图片
document.addEventListener('DOMContentLoaded', () => {const currentImages = Array.from(document.querySelectorAll('img[data-src]')).map(img => img.dataset.src);preloader.preload(currentImages, 'high');// 预加载可能的下一个页面图片const nextImages = preloader.predictNextImages(window.location.pathname);preloader.preload(nextImages, 'low');
});

🧠 第五难：JavaScript性能 - 内存管理的"收心法"

问题：如何避免内存泄漏？如何优化JavaScript执行性能？大型应用如何保持流畅运行？

深度技术：

JavaScript性能优化涉及多个层面：内存管理、执行效率、代码分割等。理解V8引擎的工作原理、垃圾回收机制，以及如何编写高性能的JavaScript代码，是提升应用性能的关键。

代码示例：

// 1. 内存泄漏检测
class MemoryLeakDetector {constructor() {this.snapshots = [];this.interval = null;}start(intervalMs = 10000) {this.interval = setInterval(() => {this.takeSnapshot();}, intervalMs);}stop() {if (this.interval) {clearInterval(this.interval);this.interval = null;}}takeSnapshot() {const snapshot = {timestamp: Date.now(),heapSize: performance.memory?.usedJSHeapSize,domNodes: document.getElementsByTagName('*').length,eventListeners: this.countEventListeners()};this.snapshots.push(snapshot);this.analyzeSnapshots();}countEventListeners() {// 获取所有元素的事件监听器数量const elements = document.getElementsByTagName('*');let count = 0;for (const element of elements) {const listeners = getEventListeners(element);count += Object.keys(listeners).length;}return count;}analyzeSnapshots() {if (this.snapshots.length < 2) return;const current = this.snapshots[this.snapshots.length - 1];const previous = this.snapshots[this.snapshots.length - 2];const heapGrowth = current.heapSize - previous.heapSize;const domGrowth = current.domNodes - previous.domNodes;const listenerGrowth = current.eventListeners - previous.eventListeners;if (heapGrowth > 1000000 || domGrowth > 100 || listenerGrowth > 50) {console.warn('Potential memory leak detected:', {heapGrowth: `${(heapGrowth / 1024 / 1024).toFixed(2)}MB`,domGrowth,listenerGrowth});}}
}// 2. 性能优化工具类
class PerformanceOptimizer {// 防抖函数debounce(func, wait) {let timeout;return function executedFunction(...args) {const later = () => {clearTimeout(timeout);func(...args);};clearTimeout(timeout);timeout = setTimeout(later, wait);};}// 节流函数throttle(func, limit) {let inThrottle;return function executedFunction(...args) {if (!inThrottle) {func(...args);inThrottle = true;setTimeout(() => inThrottle = false, limit);}};}// 批量处理batchProcess(items, processFn, batchSize = 100) {return new Promise((resolve) => {let index = 0;function processBatch() {const batch = items.slice(index, index + batchSize);if (batch.length === 0) {resolve();return;}Promise.all(batch.map(processFn)).then(() => {index += batchSize;setTimeout(processBatch, 0);});}processBatch();});}// 虚拟列表实现createVirtualList(container, items, itemHeight, renderItem) {const visibleItems = Math.ceil(container.clientHeight / itemHeight);const totalHeight = items.length * itemHeight;container.style.position = 'relative';container.style.height = `${totalHeight}px`;const visibleRange = {start: 0,end: visibleItems};function updateVisibleItems() {const scrollTop = container.scrollTop;const start = Math.floor(scrollTop / itemHeight);const end = Math.min(start + visibleItems + 1, items.length);if (start !== visibleRange.start || end !== visibleRange.end) {visibleRange.start = start;visibleRange.end = end;// 清除现有内容container.innerHTML = '';// 渲染可见项for (let i = start; i < end; i++) {const item = renderItem(items[i], i);item.style.position = 'absolute';item.style.top = `${i * itemHeight}px`;item.style.height = `${itemHeight}px`;container.appendChild(item);}}}container.addEventListener('scroll', this.throttle(updateVisibleItems, 16));updateVisibleItems();}
}// 3. 代码分割和懒加载
// webpack.config.js
module.exports = {optimization: {splitChunks: {chunks: 'all',maxInitialRequests: 10,maxAsyncRequests: 10,cacheGroups: {vendor: {test: /[\\/]node_modules[\\/]/,name: 'vendors',chunks: 'all'}}}}
};// 动态导入示例
async function loadModule(moduleName) {try {const module = await import(`./modules/${moduleName}.js`);return module;} catch (error) {console.error(`Failed to load module: ${moduleName}`, error);return null;}
}// 4. 性能监控
class PerformanceMonitor {constructor() {this.metrics = {};this.observers = new Map();}startMonitoring() {// 监控长任务this.observeLongTasks();// 监控资源加载this.observeResourceTiming();// 监控布局变化this.observeLayoutShifts();// 监控内存使用this.observeMemoryUsage();}observeLongTasks() {const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {if (entry.duration > 50) {console.warn('Long task detected:', entry);}}});observer.observe({ entryTypes: ['longtask'] });this.observers.set('longtask', observer);}observeResourceTiming() {const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {if (entry.initiatorType === 'script' && entry.duration > 1000) {console.warn('Slow script loading:', entry);}}});observer.observe({ entryTypes: ['resource'] });this.observers.set('resource', observer);}observeLayoutShifts() {const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {if (entry.value > 0.1) {console.warn('Layout shift detected:', entry);}}});observer.observe({ entryTypes: ['layout-shift'] });this.observers.set('layout-shift', observer);}observeMemoryUsage() {if (performance.memory) {setInterval(() => {const used = performance.memory.usedJSHeapSize;const total = performance.memory.totalJSHeapSize;const limit = performance.memory.jsHeapSizeLimit;if (used / limit > 0.9) {console.warn('High memory usage detected:', {used: `${(used / 1024 / 1024).toFixed(2)}MB`,total: `${(total / 1024 / 1024).toFixed(2)}MB`,limit: `${(limit / 1024 / 1024).toFixed(2)}MB`});}}, 5000);}}stopMonitoring() {for (const [type, observer] of this.observers) {observer.disconnect();}this.observers.clear();}
}// 使用示例
const optimizer = new PerformanceOptimizer();
const monitor = new PerformanceMonitor();// 启动性能监控
monitor.startMonitoring();// 使用防抖处理搜索输入
const searchInput = document.querySelector('#search');
searchInput.addEventListener('input', optimizer.debounce((e) => {// 处理搜索逻辑
}, 300));// 使用节流处理滚动事件
window.addEventListener('scroll', optimizer.throttle(() => {// 处理滚动逻辑
}, 16));// 批量处理大量数据
const items = Array.from({ length: 10000 }, (_, i) => i);
optimizer.batchProcess(items, async (item) => {// 处理单个项目
}, 100);

🎨 第六难：CSS性能 - 选择器与动画的"抱火诀"

问题：如何优化CSS选择器性能？如何实现高性能的动画效果？如何避免重排重绘？

深度技术：

CSS性能优化涉及选择器效率、动画性能、渲染优化等多个方面。理解浏览器渲染原理、CSS选择器匹配规则，以及如何编写高性能的CSS代码，是提升页面渲染性能的关键。

代码示例：

/* 1. 高性能选择器 */
/* 避免使用通配符选择器 */
* { margin: 0; padding: 0; } /* 不推荐 *//* 避免使用标签选择器 */
div { margin: 10px; } /* 不推荐 *//* 使用类选择器 */
.container { margin: 10px; } /* 推荐 *//* 避免过度嵌套 */
.nav ul li a { color: blue; } /* 不推荐 */
.nav-link { color: blue; } /* 推荐 *//* 2. 高性能动画 */
/* 使用transform和opacity进行动画 */
.animate {/* 不推荐 */left: 0;transition: left 0.3s ease;
}.animate {/* 推荐 */transform: translateX(0);transition: transform 0.3s ease;
}/* 使用will-change提示浏览器 */
.animate {will-change: transform;transform: translateX(0);transition: transform 0.3s ease;
}/* 3. 避免重排重绘 */
/* 批量修改DOM */
function batchUpdate() {// 不推荐element.style.width = '100px';element.style.height = '100px';element.style.margin = '10px';// 推荐element.style.cssText = `width: 100px;height: 100px;margin: 10px;`;
}/* 使用DocumentFragment */
function createList(items) {const fragment = document.createDocumentFragment();items.forEach(item => {const li = document.createElement('li');li.textContent = item;fragment.appendChild(li);});document.querySelector('ul').appendChild(fragment);
}/* 4. CSS性能优化工具 */
class CSSOptimizer {constructor() {this.rules = new Map();}// 分析选择器性能analyzeSelector(selector) {const complexity = this.calculateSelectorComplexity(selector);const specificity = this.calculateSpecificity(selector);return {complexity,specificity,performance: this.evaluatePerformance(complexity, specificity)};}calculateSelectorComplexity(selector) {// 计算选择器复杂度const parts = selector.split(/\s+/);return parts.length;}calculateSpecificity(selector) {// 计算选择器特异性let a = 0, b = 0, c = 0;// ID选择器a = (selector.match(/#/g) || []).length;// 类选择器、属性选择器、伪类b = (selector.match(/\.|\[|:/g) || []).length;// 元素选择器、伪元素c = (selector.match(/^[a-zA-Z]|::/g) || []).length;return { a, b, c };}evaluatePerformance(complexity, specificity) {// 评估选择器性能const score = complexity * 0.4 + (specificity.a + specificity.b + specificity.c) * 0.6;if (score < 2) return 'excellent';if (score < 4) return 'good';if (score < 6) return 'fair';return 'poor';}// 优化动画性能optimizeAnimation(element, properties) {const optimized = {};for (const [prop, value] of Object.entries(properties)) {if (prop === 'transform' || prop === 'opacity') {optimized[prop] = value;} else {console.warn(`Avoid animating ${prop}, use transform instead`);}}return optimized;}// 检测重排重绘detectReflow(element) {const originalStyle = window.getComputedStyle(element);return {before: () => {this.originalLayout = element.getBoundingClientRect();},after: () => {const newLayout = element.getBoundingClientRect();const newStyle = window.getComputedStyle(element);const hasReflow = this.originalLayout.width !== newLayout.width ||this.originalLayout.height !== newLayout.height;const hasRepaint = originalStyle.color !== newStyle.color ||originalStyle.backgroundColor !== newStyle.backgroundColor;return { hasReflow, hasRepaint };}};}
}// 使用示例
const optimizer = new CSSOptimizer();// 分析选择器性能
const selectorAnalysis = optimizer.analyzeSelector('.nav > ul > li > a');
console.log('Selector performance:', selectorAnalysis);// 优化动画
const animation = optimizer.optimizeAnimation(element, {transform: 'translateX(100px)',opacity: 0.5,width: '200px' // 不推荐
});// 检测重排重绘
const reflowDetector = optimizer.detectReflow(element);
reflowDetector.before();
// 执行可能引起重排重绘的操作
const { hasReflow, hasRepaint } = reflowDetector.after();
if (hasReflow) console.warn('Layout reflow detected');
if (hasRepaint) console.warn('Repaint detected');

📝 第七难：字体加载 - FOUT与FOIT的"隐身术"

问题：如何优化字体加载体验？如何避免字体闪烁？如何实现平滑的字体切换？

深度技术：

字体加载优化是提升用户体验的重要环节。理解FOUT（Flash of Unstyled Text）和FOIT（Flash of Invisible Text）的区别，以及如何控制字体加载行为，是优化字体显示效果的关键。

代码示例：

// 1. 字体加载策略
class FontLoader {constructor(options = {}) {this.options = {display: 'swap',timeout: 3000,...options};this.loadedFonts = new Set();}// 加载字体loadFont(fontFamily, urls) {if (this.loadedFonts.has(fontFamily)) {return Promise.resolve();}const fontFaceSet = new FontFaceSet();const fontFaces = urls.map(url => {const format = url.split('.').pop();return new FontFace(fontFamily, `url(${url})`, {style: 'normal',weight: '400',display: this.options.display});});return Promise.all(fontFaces.map(face => face.load())).then(loadedFaces => {loadedFaces.forEach(face => {document.fonts.add(face);});this.loadedFonts.add(fontFamily);}).catch(error => {console.error(`Failed to load font ${fontFamily}:`, error);});}// 预加载字体preloadFonts(fonts) {const links = fonts.map(font => {const link = document.createElement('link');link.rel = 'preload';link.href = font.url;link.as = 'font';link.crossOrigin = 'anonymous';return link;});links.forEach(link => document.head.appendChild(link));}// 监控字体加载observeFontLoading() {const observer = new FontFaceObserver('Custom Font');observer.load(null, this.options.timeout).then(() => {document.documentElement.classList.add('fonts-loaded');}).catch(() => {document.documentElement.classList.add('fonts-failed');});}
}// 2. 字体显示控制
class FontDisplayController {constructor() {this.fontDisplay = new Map();}// 设置字体显示策略setFontDisplay(fontFamily, display) {this.fontDisplay.set(fontFamily, display);const style = document.createElement('style');style.textContent = `@font-face {font-family: ${fontFamily};font-display: ${display};}`;document.head.appendChild(style);}// 获取字体加载状态getFontStatus(fontFamily) {return document.fonts.check(`12px "${fontFamily}"`);}// 监听字体加载完成onFontLoaded(fontFamily, callback) {if (this.getFontStatus(fontFamily)) {callback();return;}document.fonts.ready.then(() => {if (this.getFontStatus(fontFamily)) {callback();}});}
}// 3. 字体回退策略
class FontFallback {constructor() {this.fallbacks = new Map();}// 设置字体回退链setFallback(fontFamily, fallbackChain) {this.fallbacks.set(fontFamily, fallbackChain);const style = document.createElement('style');style.textContent = `.${fontFamily} {font-family: ${fallbackChain.join(', ')};}`;document.head.appendChild(style);}// 应用字体回退applyFallback(element, fontFamily) {const fallbackChain = this.fallbacks.get(fontFamily);if (fallbackChain) {element.style.fontFamily = fallbackChain.join(', ');}}
}// 使用示例
const fontLoader = new FontLoader({display: 'swap',timeout: 3000
});const displayController = new FontDisplayController();
const fontFallback = new FontFallback();// 加载自定义字体
fontLoader.loadFont('Custom Font', ['/fonts/custom-font.woff2','/fonts/custom-font.woff'
]);// 设置字体显示策略
displayController.setFontDisplay('Custom Font', 'swap');// 设置字体回退
fontFallback.setFallback('Custom Font', ['Custom Font','Arial','sans-serif'
]);// 监听字体加载
displayController.onFontLoaded('Custom Font', () => {document.body.classList.add('custom-font-loaded');
});// 预加载字体
fontLoader.preloadFonts([{ url: '/fonts/custom-font.woff2' }
]);// 监控字体加载
fontLoader.observeFontLoading();

🔮 第八难：预加载技术 - Prefetch与Preload的"千里眼"

问题：如何预测用户行为并预加载资源？如何平衡预加载与性能消耗？如何实现智能预加载策略？

深度技术：

预加载技术是提升用户体验的重要手段，通过预测用户行为并提前加载资源，可以显著减少等待时间。理解不同预加载策略的特点和适用场景，是优化资源加载效率的关键。

代码示例：

// 1. 预加载管理器
class PreloadManager {constructor() {this.prefetchQueue = new Set();this.preloadQueue = new Set();this.maxConcurrent = 3;this.currentLoading = 0;}// 预获取资源prefetch(url, options = {}) {if (this.prefetchQueue.has(url)) return;this.prefetchQueue.add(url);this.processPrefetchQueue();}// 预加载资源preload(url, options = {}) {if (this.preloadQueue.has(url)) return;this.preloadQueue.add(url);this.processPreloadQueue();}// 处理预获取队列processPrefetchQueue() {if (this.currentLoading >= this.maxConcurrent) return;const url = Array.from(this.prefetchQueue)[0];if (!url) return;this.prefetchQueue.delete(url);this.currentLoading++;const link = document.createElement('link');link.rel = 'prefetch';link.href = url;link.onload = () => {this.currentLoading--;this.processPrefetchQueue();};link.onerror = () => {this.currentLoading--;this.processPrefetchQueue();};document.head.appendChild(link);}// 处理预加载队列processPreloadQueue() {if (this.currentLoading >= this.maxConcurrent) return;const url = Array.from(this.preloadQueue)[0];if (!url) return;this.preloadQueue.delete(url);this.currentLoading++;const link = document.createElement('link');link.rel = 'preload';link.href = url;link.as = this.getResourceType(url);link.onload = () => {this.currentLoading--;this.processPreloadQueue();};link.onerror = () => {this.currentLoading--;this.processPreloadQueue();};document.head.appendChild(link);}// 获取资源类型getResourceType(url) {const extension = url.split('.').pop().toLowerCase();switch (extension) {case 'js':return 'script';case 'css':return 'style';case 'jpg':case 'jpeg':case 'png':case 'gif':case 'webp':return 'image';case 'woff':case 'woff2':case 'ttf':case 'otf':return 'font';default:return 'fetch';}}
}// 2. 智能预加载
class SmartPreloader {constructor() {this.preloadManager = new PreloadManager();this.userBehavior = new Map();this.threshold = 0.7;}// 记录用户行为recordBehavior(action, target) {const key = `${action}-${target}`;this.userBehavior.set(key, (this.userBehavior.get(key) || 0) + 1);}// 预测下一个动作predictNextAction(currentAction) {const predictions = new Map();for (const [key, count] of this.userBehavior) {const [action, target] = key.split('-');if (action === currentAction) {predictions.set(target, count);}}return Array.from(predictions.entries()).filter(([_, count]) => count > this.threshold).sort((a, b) => b[1] - a[1]).map(([target]) => target);}// 预加载预测资源preloadPredictedResources(currentAction) {const predictedTargets = this.predictNextAction(currentAction);predictedTargets.forEach(target => {const resources = this.getResourcesForTarget(target);resources.forEach(resource => {this.preloadManager.preload(resource);});});}// 获取目标相关资源getResourcesForTarget(target) {// 根据目标返回需要预加载的资源const resourceMap = {'home': ['/styles/home.css', '/scripts/home.js'],'products': ['/styles/products.css', '/scripts/products.js'],'about': ['/styles/about.css', '/scripts/about.js']};return resourceMap[target] || [];}
}// 3. 路由预加载
class RoutePreloader {constructor() {this.preloadManager = new PreloadManager();this.routes = new Map();}// 注册路由registerRoute(path, resources) {this.routes.set(path, resources);}// 预加载路由资源preloadRoute(path) {const resources = this.routes.get(path);if (resources) {resources.forEach(resource => {this.preloadManager.preload(resource);});}}// 监听路由变化observeRouteChanges() {let lastPath = window.location.pathname;// 监听点击事件document.addEventListener('click', (event) => {const link = event.target.closest('a');if (link && link.href.startsWith(window.location.origin)) {const path = new URL(link.href).pathname;this.preloadRoute(path);}});// 监听路由变化window.addEventListener('popstate', () => {const currentPath = window.location.pathname;if (currentPath !== lastPath) {this.preloadRoute(currentPath);lastPath = currentPath;}});}
}// 使用示例
const preloadManager = new PreloadManager();
const smartPreloader = new SmartPreloader();
const routePreloader = new RoutePreloader();// 预获取资源
preloadManager.prefetch('/images/hero.jpg');
preloadManager.prefetch('/styles/main.css');// 预加载资源
preloadManager.preload('/scripts/main.js');
preloadManager.preload('/fonts/custom-font.woff2');// 记录用户行为
smartPreloader.recordBehavior('click', 'products');
smartPreloader.recordBehavior('click', 'about');// 预加载预测资源
smartPreloader.preloadPredictedResources('click');// 注册路由
routePreloader.registerRoute('/products', ['/styles/products.css','/scripts/products.js'
]);// 监听路由变化
routePreloader.observeRouteChanges();

📊 第九难：性能监控 - 前端埋点的"顺风耳"

问题：如何全面监控前端性能？如何收集和分析性能数据？如何建立性能监控体系？

深度技术：

性能监控是优化前端性能的基础，通过收集和分析性能数据，可以发现问题并持续改进。理解性能指标、监控方法和数据分析技术，是建立完整性能监控体系的关键。

代码示例：

// 1. 性能监控器
class PerformanceMonitor {constructor() {this.metrics = {};this.observers = new Map();}// 监控核心性能指标monitorCoreWebVitals() {// 监控LCP (Largest Contentful Paint)this.observeLCP();// 监控FID (First Input Delay)this.observeFID();// 监控CLS (Cumulative Layout Shift)this.observeCLS();}// 监控LCPobserveLCP() {const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {this.metrics.lcp = entry.startTime;this.reportMetric('lcp', entry.startTime);}});observer.observe({ entryTypes: ['largest-contentful-paint'] });this.observers.set('lcp', observer);}// 监控FIDobserveFID() {const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {this.metrics.fid = entry.processingStart - entry.startTime;this.reportMetric('fid', this.metrics.fid);}});observer.observe({ entryTypes: ['first-input'] });this.observers.set('fid', observer);}// 监控CLSobserveCLS() {let clsValue = 0;let clsEntries = [];const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {if (!entry.hadRecentInput) {clsValue += entry.value;clsEntries.push(entry);}}this.metrics.cls = clsValue;this.reportMetric('cls', clsValue);});observer.observe({ entryTypes: ['layout-shift'] });this.observers.set('cls', observer);}// 监控资源加载monitorResourceLoading() {const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {if (entry.initiatorType === 'script' && entry.duration > 1000) {this.reportMetric('slow-script', {url: entry.name,duration: entry.duration});}}});observer.observe({ entryTypes: ['resource'] });this.observers.set('resource', observer);}// 监控长任务monitorLongTasks() {const observer = new PerformanceObserver((list) => {for (const entry of list.getEntries()) {if (entry.duration > 50) {this.reportMetric('long-task', {duration: entry.duration,startTime: entry.startTime});}}});observer.observe({ entryTypes: ['longtask'] });this.observers.set('longtask', observer);}// 监控内存使用monitorMemoryUsage() {if (performance.memory) {setInterval(() => {const used = performance.memory.usedJSHeapSize;const total = performance.memory.totalJSHeapSize;const limit = performance.memory.jsHeapSizeLimit;this.reportMetric('memory', {used,total,limit});}, 5000);}}// 报告性能指标reportMetric(name, value) {// 发送到性能监控服务console.log(`Metric: ${name}`, value);// 可以发送到后端API// fetch('/api/metrics', {//   method: 'POST',//   body: JSON.stringify({ name, value })// });}// 停止监控stopMonitoring() {for (const [type, observer] of this.observers) {observer.disconnect();}this.observers.clear();}
}// 2. 性能数据收集器
class PerformanceCollector {constructor() {this.data = new Map();}// 收集性能指标collectMetrics() {// 收集导航计时const navigation = performance.getEntriesByType('navigation')[0];this.data.set('navigation', {dns: navigation.domainLookupEnd - navigation.domainLookupStart,tcp: navigation.connectEnd - navigation.connectStart,request: navigation.responseEnd - navigation.requestStart,dom: navigation.domComplete - navigation.domLoading,load: navigation.loadEventEnd - navigation.loadEventStart});// 收集资源计时const resources = performance.getEntriesByType('resource');this.data.set('resources', resources.map(resource => ({url: resource.name,type: resource.initiatorType,duration: resource.duration,size: resource.transferSize})));// 收集用户计时const userTiming = performance.getEntriesByType('measure');this.data.set('userTiming', userTiming.map(measure => ({name: measure.name,duration: measure.duration})));}// 收集错误信息collectErrors() {const errors = [];window.addEventListener('error', (event) => {errors.push({type: 'error',message: event.message,filename: event.filename,lineno: event.lineno,colno: event.colno,stack: event.error?.stack});});window.addEventListener('unhandledrejection', (event) => {errors.push({type: 'unhandledrejection',message: event.reason?.message || event.reason,stack: event.reason?.stack});});this.data.set('errors', errors);}// 收集用户行为collectUserBehavior() {const behavior = [];// 记录点击事件document.addEventListener('click', (event) => {behavior.push({type: 'click',target: event.target.tagName,timestamp: Date.now()});});// 记录滚动事件let scrollTimeout;window.addEventListener('scroll', () => {clearTimeout(scrollTimeout);scrollTimeout = setTimeout(() => {behavior.push({type: 'scroll',position: window.scrollY,timestamp: Date.now()});}, 100);});this.data.set('behavior', behavior);}// 获取收集的数据getData() {return Object.fromEntries(this.data);}
}// 3. 性能分析器
class PerformanceAnalyzer {constructor(data) {this.data = data;}// 分析性能问题analyze() {const issues = [];// 分析加载时间const navigation = this.data.navigation;if (navigation.dom > 1000) {issues.push({type: 'slow-dom',message: 'DOM加载时间过长',value: navigation.dom});}// 分析资源加载const resources = this.data.resources;const slowResources = resources.filter(r => r.duration > 1000);if (slowResources.length > 0) {issues.push({type: 'slow-resources',message: '存在慢资源加载',resources: slowResources});}// 分析错误const errors = this.data.errors;if (errors.length > 0) {issues.push({type: 'errors',message: '存在未处理的错误',errors});}return issues;}// 生成性能报告generateReport() {const issues = this.analyze();return {timestamp: Date.now(),metrics: this.data,issues,recommendations: this.generateRecommendations(issues)};}// 生成优化建议generateRecommendations(issues) {const recommendations = [];issues.forEach(issue => {switch (issue.type) {case 'slow-dom':recommendations.push({type: 'dom',message: '考虑优化DOM结构，减少DOM节点数量'});break;case 'slow-resources':recommendations.push({type: 'resources',message: '考虑使用CDN加速资源加载，或优化资源大小'});break;case 'errors':recommendations.push({type: 'errors',message: '建议添加错误监控和自动上报机制'});break;}});return recommendations;}
}// 使用示例
const monitor = new PerformanceMonitor();
const collector = new PerformanceCollector();
const analyzer = new PerformanceAnalyzer(collector.getData());// 启动性能监控
monitor.monitorCoreWebVitals();
monitor.monitorResourceLoading();
monitor.monitorLongTasks();
monitor.monitorMemoryUsage();// 收集性能数据
collector.collectMetrics();
collector.collectErrors();
collector.collectUserBehavior();// 分析性能问题
const report = analyzer.generateReport();
console.log('Performance Report:', report);// 停止监控
monitor.stopMonitoring();