前端优化：图片延迟加载

<img src="data:image/png;base64,R0lGODlhAQABAAD/ACwAAAAAAQABAAACADs=" data-src="a.jpg">

function loadImage(){
    var deferImages=document.getElementsByTagName(‘img‘);
    var curImg;
    var imgSrc;
    for(var i=0,len=deferImages.length;i<len;i++){
        curImg=deferImages[i];
        imgSrc=curImg.getAttribute(‘data-src‘);
        if(imgSrc){
            curImg.setAttribute(‘src‘,imgSrc);
        }
    }
}

window.onload=loadImage;