这篇文章主要介绍了使用原生javascript实现图片滚动、延时加载功能,思路与方法均分享给大家,希望对大家能有所帮助。
实现效果:下拉滚动条时,图片出现在可见区域时,才开始加载
思路:
(1)img标签,把真实的图片地址,放在自己设置的属性里面,如 lazy-src
(2)获取img离页面的高度(在JQ里是offset().top),原生是:
img.getBoundingClientRect().top + document.body.scrollTop||document.documentElement.scrollTop
(3)判断img出现的位置是否在可见区域里:
在浏览器的可见区域,justTop>scrollTop&&offsetTop<(scrollTop+windowHeight),这里的justTop是图片的offsetTop+图片高度
//保存document在变量里,减少对document的查询 var doc = document; for(var n=0,i = this.oImg.length;n<i;n++){ //获取图片占位符图片地址 var hSrc = this.oImg[n].getAttribute(this.sHolder_src); if(hSrc){ var scrollTop = doc.body.scrollTop||doc.documentElement.scrollTop, windowHeight = doc.documentElement.clientHeight, offsetTop = this.oImg[n].getBoundingClientRect().top + scrollTop, imgHeight = this.oImg[n].clientHeight, justTop = offsetTop + imgHeight; // 判断图片是否在可见区域 if(justTop>scrollTop&&offsetTop<(scrollTop+windowHeight)){ this.isLoad(hSrc,n); } } }
以下为详细代码:
function LGY_imgScrollLoad(option){ this.oImg = document.getElementById(option.wrapID).getElementsByTagName('img'); this.sHolder_src = option.holder_src; this.int(); } LGY_imgScrollLoad.prototype = { loadImg:function(){ //保存document在变量里,减少对document的查询 var doc = document; for(var n=0,i = this.oImg.length;n<i;n++){ //获取图片占位符图片地址 var hSrc = this.oImg[n].getAttribute(this.sHolder_src); if(hSrc){ var scrollTop = doc.body.scrollTop||doc.documentElement.scrollTop, windowHeight = doc.documentElement.clientHeight, offsetTop = this.oImg[n].getBoundingClientRect().top + scrollTop, imgHeight = this.oImg[n].clientHeight, justTop = offsetTop + imgHeight; // 判断图片是否在可见区域 if(justTop>scrollTop&&offsetTop<(scrollTop+windowHeight)){ //alert(offsetTop); this.isLoad(hSrc,n); } } } }, isLoad:function(src,n){ var src = src, n = n, o_img = new Image(), _that = this; o_img.onload = (function(n){ _that.oImg[n].setAttribute('src',src); _that.oImg[n].removeAttribute(_that.sHolder_src); })(n); o_img.src = src; }, int:function(){ this.loadImg(); var _that = this, timer = null; // 滚动:添加定时器,防止频繁调用loadImg函数 window.onscroll = function(){ clearTimeout(timer); timer = setTimeout(function(){ _that.loadImg(); },100); } } }
效果图:
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