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图片懒加载--判断div ul中的li是否已经滑动到可视区域里

<!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>
<!-- 参考网址  https://segmentfault.com/a/1190000003881643 -->
<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>
这是整个页面的代码。其中有gitH()函数和判断是否在可视区域。
加油。
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原文地址：https://www.cnblogs.com/xiaoxiao2014/p/6070271.html