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function
getElementsByClassName(str,root,tag){ if(root){ root = typeof
root == "string"
? document.getElementById(root) : root; } else
{ root = document.body; } tag = tag || "*"; var
els = root.getElementsByTagName(tag),arr = []; for(var
i=0,n=els.length;i<n;i++){ //k是一个数组 for(var
j=0,k=els[i].className.split(" "),l=k.length;j<l;j++){ if(k[j] == str){ arr.push(els[i]); break; } } } return
arr; } //取元素的页面绝对 X位置 function
getLeft(El){ var
left = 0; do{ left += El.offsetLeft; }while((El = El.offsetParent).nodeName != ‘BODY‘); return
left; }; //取元素的页面绝对 Y位置 function
getTop(obj){ var
top = 0; while(obj){ top += obj.offsetTop; obj = obj.offsetParent; } return
top; }; function
lazyLoad(){ var
imgs =getElementsByClassName("lazyLoad",null,"img"), top = document.body.scrollTop || document.documentElement.scrollTop, left = document.body.scrollLeft || document.documentElement.scrollLeft, screenHeight = window.screen.height, screenWidth = window.screen.width; for(var
i=0,len=imgs.length; i < len; i++){ var
_top = getTop(imgs[i]); var
_left = getLeft(imgs[i]); //判断图片是否在显示区域内 if(_top <= screenHeight+top && _left <= screenWidth+left){ var
_src = imgs[i].getAttribute(‘_src‘); //如果图片已经显示，则取消赋值 if(/imgs\/load.jpg$/.test(imgs[i].getAttribute(‘src‘))){ imgs[i].src = _src; } } } } window.onload = window.onscroll = window.onresize= lazyLoad; |
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<% for(int i = 0; i < 21; i++){ %> <img _src="imgs/img<%=i%>.jpg"
class="lazyLoad"
id="<%=i%>"
data-i = <%=i%> src="imgs/load.jpg"
style="width:590px;height:500px;"> <% } |
关键点是1，把图片的src保存在自定义属性中，src统一用同一图片，浏览器会自动缓存。2，当图片出现在视口中则把src替换为真实的路径。这个时候会产生http请求，图片就加载了出来
纯js懒加载，java后台举例,布布扣,bubuko.com
原文：http://www.cnblogs.com/stay-poor/p/3721842.html