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nction loadImage(img) { const lazySrc = img.getAttribute("lazy-src"); if (!lazySrc) return; // 清除延迟标记（如果存在） img.removeAttribute("lazy-delay-started"); // 设置父容器样式 const parent = img.parentElement; if (!parent) return; // 获取之前设置的占位符 const placeholderId = img.getAttribute("placeholder-element-id"); const placeholderElement = placeholderId ? parent.querySelector(`[data-placeholder-id="${placeholderId}"]`) : null; // 图片加载成功处理 img.onload = function () { img.style.display = ""; img.style.width = "100%"; img.style.height = "100%"; // 移除占位符 if (placeholderElement) { placeholderElement.style.display = "none"; parent.removeChild(placeholderElement); } // 清除懒加载相关属性 img.removeAttribute("lazy-src"); img.removeAttribute("lazy-placeholder"); img.removeAttribute("lazy-delay"); img.removeAttribute("placeholder-setup"); img.removeAttribute("placeholder-element-id"); }; // 设置图片源 img.src = lazySrc; } // 防抖函数 function debounce(func, wait) { let timeout; return function() { const context = this; const args = arguments; clearTimeout(timeout); timeout = setTimeout(() => { func.apply(context, args); }, wait); }; } // 检查元素是否在视口内且可见 function isElementInViewport(el) { // 检查元素或其任何父元素是否为display:none function isVisible(element) { if (!element) return true; // 获取元素的计算样式 const style = window.getComputedStyle(element); if (style.display === 'none') return false; // 递归检查父元素 return isVisible(element.parentElement); } // 如果元素不可见，直接返回false if (!isVisible(el)) return false; // 检查元素是否在视口内 const rect = el.getBoundingClientRect(); return ( rect.top >= 0 && rect.left >= 0 && rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) && rect.right <= (window.innerWidth || document.documentElement.clientWidth) ); } // 滚动事件处理函数 function handleScroll() { const lazyImages = document.querySelectorAll("img[lazy-src]"); lazyImages.forEach((img) => { if (isElementInViewport(img)) { // 先设置占位符 setupPlaceholder(img); const delay = img.getAttribute("lazy-delay"); if (delay && !isNaN(parseInt(delay))) { // 如果设置了延迟且尚未开始延迟加载 if (!img.hasAttribute("lazy-delay-started")) { img.setAttribute("lazy-delay-started", "true"); setTimeout(() => { loadImage(img); }, parseInt(delay)); } } else { loadImage(img); } } }); // 如果没有需要懒加载的图片了，移除滚动事件监听 if (document.querySelectorAll("img[lazy-src]").length === 0) { window.removeEventListener("scroll", debouncedHandleScroll); window.removeEventListener("resize", debouncedHandleScroll); document.removeEventListener("DOMSubtreeModified", debouncedHandleScroll); } } // 创建防抖版本的滚动处理函数 const debouncedHandleScroll = debounce(handleScroll, 200); // 使用滚动事件实现懒加载（用于不支持IntersectionObserver的浏览器） function setupScrollBasedLazyLoad() { // 初始检查一次视口内的图片 handleScroll(); // 添加滚动事件监听（使用防抖） window.addEventListener("scroll", debouncedHandleScroll); // 添加调整窗口大小事件监听（使用防抖） window.addEventListener("resize", debouncedHandleScroll); // 监听DOM变化，处理父元素从display:none变为block的情况 document.addEventListener("DOMSubtreeModified", debouncedHandleScroll); // 使用MutationObserver监听DOM变化（如果浏览器支持） if (window.MutationObserver) { const mutationObserver = new MutationObserver(debouncedHandleScroll); mutationObserver.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] }); } } // 初始化函数 function init() { if (isIntersectionObserverSupported) { // 支持IntersectionObserver，使用懒加载 const lazyImages = document.querySelectorAll("img[lazy-src]"); lazyImages.forEach((img) => { observer.observe(img); }); } else { // 不支持IntersectionObserver，使用基于滚动事件的懒加载 setupScrollBasedLazyLoad(); } } // 当DOM加载完成后初始化 if (document.readyState === "loading") { document.addEventListener("DOMContentLoaded", init); } else { init(); } })();

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