web前端图片懒加载

(function(){var imgList=[];//懒加载图片组成的数组var timer;//计时器var offset=0;//偏移量function imgShow(el){//判断img是否出现在可视窗口        var positions = el.getBoundingClientRect();        return positions.top <= (document.documentElement.clientHeight || window.innerHeight) + parseInt(offset);    };function imgLoading(el){//滚动监听        var  els = document.querySelectorAll(el);        imgList = Array.apply(null,els);        window.addEventListener('scroll',function(){        clearTimeout(timer);        timer=setTimeout(function(){        for(var i = 0 ; i < imgList.length; i++){            if(imgShow(imgList[i])){                imgList[i].src = imgList[i].getAttribute('data-src');                imgList.splice(i,1);            }        }        },300);        },false)    };    imgLoading('.imgLazyLoad');})();