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:
来源: http://www.phperz.com/article/17/0412/273397.html