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
复制代码 代码如下:
//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:
复制代码 代码如下:
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);
}
}