classDynamicSizeVirtualScrollextendsVirtualScroll{constructor(options){super(options)this.sizeMap =newMap()}handleScroll(){const scrollTop =this.container.scrollTop
this.startIndex =this.findNearestIndex(scrollTop)this.endIndex =this.findNearestIndex(scrollTop +this.container.clientHeight)this.updateVisibleData()}findNearestIndex(scrollTop){let totalHeight =0for(let i =0; i <this.data.length; i++){const height =this.sizeMap.get(i)||this.itemHeight
if(totalHeight + height >= scrollTop){return i
}
totalHeight += height
}returnthis.data.length -1}updateContainerStyle(){let totalHeight =0const positions =[]for(let i =0; i <this.data.length; i++){
positions[i]= totalHeight
totalHeight +=this.sizeMap.get(i)||this.itemHeight
}this.phantomEl.style.height =`${totalHeight}px`const startOffset = positions[this.startIndex]this.contentEl.style.transform =`translateY(${startOffset}px)`}}
四、性能优化策略
4.1 内存回收机制
classDOMRecycler{constructor(){this.pool =newMap()this.active =newSet()}getDOM(type){if(this.pool.has(type)&&this.pool.get(type).size >0){const dom =this.pool.get(type).values().next().value
this.pool.get(type).delete(dom)this.active.add(dom)return dom
}returnthis.createDOM(type)}createDOM(type){const dom = document.createElement(type)this.active.add(dom)return dom
}recycle(dom){const type = dom.tagName.toLowerCase()if(!this.pool.has(type)){this.pool.set(type,newSet())}this.active.delete(dom)this.pool.get(type).add(dom)
dom.style.display ='none'}}
functionchunkRender(items, container){constCHUNK_SIZE=50let index =0functionrenderChunk(){const fragment = document.createDocumentFragment()const end = Math.min(index +CHUNK_SIZE, items.length)for(; index < end; index++){const item = document.createElement('div')
item.textContent = items[index]
fragment.appendChild(item)}
container.appendChild(fragment)if(index < items.length){requestIdleCallback(renderChunk)}}requestIdleCallback(renderChunk)}
6.2 预加载策略
classPreloader{constructor(){this.cache =newMap()}prefetch(start, end){for(let i = start; i < end; i++){if(!this.cache.has(i)){this.cache.set(i,this.fetchData(i))}}}fetchData(index){returnnewPromise(resolve=>{// 模拟异步请求setTimeout(()=>{resolve(`Data for ${index}`)}, Math.random()*500)})}}