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JS implementation of image lazy loading tutorial

巴扎黑

Jul 17, 2017 pm 02:59 PM

loadpicture

Image lazy loading,

Idea: When the mouse slides to the height of the corresponding image, the image is loaded;

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
		<style type="text/css">
			#div{
				width: 575px;
				height: auto;
                overflow: hidden;
                border: red 1px solid;
                margin: 0 auto;
                /*给该div设置定位*/
                position: relative;
			}
			#div img{
				width: 267px;
				height: 396px;
				margin-left: 10px;
				border: 1px solid #000;
			}
		</style>
		<script type="text/javascript">
			function getPos(obj){
				var l = 0;
				var t = 0;
				while(obj){
					
					l += obj.offsetLeft;
					t += obj.offsetTop;
					obj = obj.offsetParent;
				}
				return {left:l ,top : t}
			}
			window.onload = window.onscroll =  function(){
				//获取到img
				    var aImg = document.getElementsByTagName("img");
				//获取到它的scrollTop 值   考虑兼容问题
					var oScrollTop = document.documentElement.scrollTop || document.body.scrollTop;
//				 clientHeight = 上下padding + height
					var clientH = document.documentElement.clientHeight;
					//循环遍历每一项通过调用获取到每一个i 项对象的top 值
					for (var i = 0;i<aImg.length;i++) {
						var aImgTop = getPos(aImg[i]).top;
//						当滚动的时候进行判断,看他的滚动的高度加上它的clientHeight  是否比它的 top 值大   
//						如果大或等于说明滚动到当前位置可以加载图片
						if (oScrollTop + clientH >= aImgTop) {
//							进行图片的加载
							aImg[i].src = aImg[i].getAttribute("_src");
						}
					}
			}
		</script>
	</head>
	<body>
		<div id="div">
			<img  src="/static/imghwm/default1.png"  data-src="../img/1.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/2.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/3.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/4.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/6.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/7.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/1.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/2.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/3.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/4.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/6.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/7.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/3.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/4.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/6.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
			<img  src="/static/imghwm/default1.png"  data-src="../img/7.jpg"  class="lazy"  _/ alt="JS implementation of image lazy loading tutorial" >
		</div>
	</body>
</html>

When Loading mode commonly used when there is a layout similar to waterfall flow

<script>
var num = document.getElementsByTagName(&#39;img&#39;).length;
var img = document.getElementsByTagName("img");
var n = 0; //存储图片加载到的位置，避免每次都从第一张图片开始遍历
lazyload(); //页面载入完毕加载可是区域内的图片
window.onscroll = lazyload;
function lazyload() { //监听页面滚动事件
var seeHeight = document.documentElement.clientHeight; //可见区域高度
var scrollTop = document.documentElement.scrollTop || document.body.scrollTop; //滚动条距离顶部高度
for (var i = n; i < num; i++) {
if (img[i].offsetTop < seeHeight + scrollTop) {
if (img[i].getAttribute("src") == "") {
img[i].src = img[i].getAttribute("data-src");
}
n = i + 1;
}
}
}
</script>

<script>
var n = 0,
imgNum = $("img").length,
img = $(&#39;img&#39;);
lazyload();
$(window).scroll(lazyload);
function lazyload(event) {
for (var i = n; i < imgNum; i++) {
if (img.eq(i).offset().top < parseInt($(window).height()) + parseInt($(window).scrollTop())) {
if (img.eq(i).attr("src") == "") {
var src = img.eq(i).attr("data-src");
img.eq(i).attr("src", src);
n = i + 1;
}
}
}
}
</script>

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