JavaScript性能优化实战指南（详尽分解版）

JavaScript性能优化实战指南

一、加载优化

减少HTTP请求

// 合并CSS/JS文件
// 使用雪碧图CSS Sprites
.icon {background-image: url(sprites.png);background-position: -20px 0;
}

代码分割与懒加载

// 动态导入模块
button.addEventListener('click', async () => {const module = await import('./largeModule.js');module.run();
});// React懒加载
const LazyComponent = React.lazy(() => import('./Component'));

二、执行效率优化

避免长任务阻塞

// 分解任务
function processChunk(start) {for(let i = start; i < Math.min(start + 100, data.length); i++) {// 处理数据}if(start < data.length) {requestIdleCallback(() => processChunk(start + 100));}
}// Web Workers示例
const worker = new Worker('worker.js');
worker.postMessage(largeData);

事件处理优化

// 事件委托
document.getElementById('list').addEventListener('click', (e) => {if(e.target.tagName === 'LI') {handleItemClick(e.target);}
});// 滚动优化
let ticking = false;
window.addEventListener('scroll', () => {if(!ticking) {requestAnimationFrame(() => {updatePosition();ticking = false;});ticking = true;}
});

三、内存管理

避免内存泄漏

// 清除定时器
const timer = setInterval(() => {...}, 1000);
componentWillUnmount() {clearInterval(timer);
}// 解除DOM引用
let elements = document.getElementsByClassName('item');
elements = null;// 使用WeakMap
const weakCache = new WeakMap();
function cacheData(obj, data) {weakCache.set(obj, data);
}

对象池技术

class ObjectPool {constructor(createFn) {this.pool = [];this.createFn = createFn;}get() {return this.pool.pop() || this.createFn();}release(obj) {this.pool.push(obj);}
}// 使用示例
const particlePool = new ObjectPool(() => new Particle());
const p = particlePool.get();
// 使用后回收
particlePool.release(p);

四、渲染优化

减少重排重绘

// 批量DOM操作
const fragment = document.createDocumentFragment();
for(let i=0; i<100; i++){const div = document.createElement('div');fragment.appendChild(div);
}
container.appendChild(fragment);// GPU加速动画
.element {transform: translateZ(0);will-change: transform;
}

虚拟滚动实现

class VirtualScroll {constructor(container, items, itemHeight) {this.container = container;this.items = items;this.itemHeight = itemHeight;this.visibleCount = Math.ceil(container.clientHeight / itemHeight);this.startIndex = 0;container.addEventListener('scroll', this.handleScroll.bind(this));this.render();}handleScroll() {const newStart = Math.floor(this.container.scrollTop / this.itemHeight);if(newStart !== this.startIndex) {this.startIndex = newStart;this.render();}}render() {const endIndex = this.startIndex + this.visibleCount;const visibleItems = this.items.slice(this.startIndex, endIndex);// 更新DOM逻辑// 复用现有DOM节点}
}

五、网络请求优化

资源压缩与缓存

# .htaccess配置示例
<IfModule mod_deflate.c>AddOutputFilterByType DEFLATE text/html text/css application/javascript
</IfModule><IfModule mod_expires.c>ExpiresActive OnExpiresByType image/jpeg "access plus 1 year"
</IfModule>

数据缓存策略

const cache = new Map();async function fetchData(url) {if(cache.has(url)) {return cache.get(url);}const data = await fetch(url).then(res => res.json());cache.set(url, data);// 本地持久化存储try {localStorage.setItem(url, JSON.stringify(data));} catch(e) {}return data;
}

六、性能分析工具

Chrome DevTools使用技巧
- Performance面板录制分析
- Memory面板堆快照分析
- Coverage面板检测未使用代码
Lighthouse优化建议

npm install -g lighthouse
lighthouse https://example.com --view

七、高级优化技巧

WebAssembly应用

// 加载WebAssembly模块
WebAssembly.instantiateStreaming(fetch('module.wasm')).then(obj => {const result = obj.instance.exports.heavyCalculation();});

算法复杂度优化

// O(n)替代O(n^2)
// 未优化
function findPair(arr, target) {for(let i=0; i<arr.length; i++) {for(let j=i+1; j<arr.length; j++) {if(arr[i] + arr[j] === target) return true;}}return false;
}// 优化后
function findPairOptimized(arr, target) {const seen = new Set();for(const num of arr) {const complement = target - num;if(seen.has(complement)) return true;seen.add(num);}return false;
}