图片懒加载--判断div ul中的li是否已经滑动到可视区域里

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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0, user-scalable=0, minimum-scale=1.0, maximum-scale=1.0">
<title>lazyLoad</title>

<style type="text/css" media="all">
* {
margin: 0;
padding: 0;
} #div1 {
width: 520px;
margin: 30px auto;
border: 1px solid red;
overflow: hidden;
} li {
width: 160px;
height: 160px;
float: left;
list-style: none;
margin: 5px;
background: url(loading.gif) center center no-repeat;
border: 1px dashed green;
}
img{
width:100%
}
</style>
</head>
<body>
<div id="div1">
<ul>
<li data-src="http://4493bz.1985t.com/uploads/allimg/140710/1-140G0161612.jpg"></li>
<li data-src="http://4493bz.1985t.com/uploads/allimg/140628/1-14062Q33R6.jpg"></li>
<li data-src="http://4493bz.1985t.com/uploads/allimg/140628/1-14062Q33242.jpg"></li>
<li data-src="http://img.bizhi.sogou.com/images/2014/12/10/997251.jpg"></li>
<li data-src="http://dl.bizhi.sogou.com/images/2014/12/02/986640.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170473_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170475_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170477_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
<li data-src="http://imgstore.cdn.sogou.com/app/a/100540002/1170479_s_90_2_219x160.jpg"></li>
</ul>
</div>
<script>
window.onload = function () {
window.onscroll();
};
window.onscroll = function () {
var oDiv = document.getElementById('div1');
var oUl = oDiv.children[0];
var aLi = oUl.children; for (var i = 0, l = aLi.length; i < l; i++) {
var oLi = aLi[i];
//检查oLi是否在可视区域
var t = document.documentElement.clientHeight + (document.documentElement.scrollTop || document.body.scrollTop);
var h = getH(oLi);
if (h < t) {
setTimeout("setImg(" + i + ")", 500);
}
console.log(i);
}
};
function setImg(index){
var oDiv=document.getElementById("div1")
var oUl=oDiv.children[0];
var aLi=oUl.children;
if (aLi[index].dataset) {
var src=aLi[index].dataset.src;
} else{
var src=aLi[index].getAttribute('data-src');
}
var oImg=document.createElement('img');
oImg.src=src;
if (aLi[index].children.length==0) {
aLi[index].appendChild(oImg);
}
}
//获得对象距离页面顶端的距离
function getH(obj) {
var h = 0;
while (obj) {
h += obj.offsetTop;
obj = obj.offsetParent;
}
return h;
}
</script>
</body>
</html>