原生javascript-图片滚动加载
下拉滚动条时，图片出现在可见区域时，才开始加载：个人在线实例：http://www.lgyweb.com/imgScrollLoad/
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
//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);
}
}
}
复制代码
以下为详细代码：
复制代码
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);
}
}
}
