//图片懒加载开始
var imgs = document.querySelectorAll('img[data-src]');
//offsetTop是元素与offsetParent的距离，循环获取直到页面顶部
function getTop(e) {
    var T = e.offsetTop;
    while (e = e.offsetParent) {
        T += e.offsetTop;
    }
    return T;
}

function lazyLoad(imgs) {
    var H = document.documentElement.clientHeight;//获取可视区域高度
    var S = document.documentElement.scrollTop || document.body.scrollTop;
    for (var i = 0; i < imgs.length; i++) {
        if (H + S > getTop(imgs[i])) {
            imgs[i].src = imgs[i].getAttribute('data-src');
        }
    }
}

window.onload = window.onscroll = function () { //onscroll()在滚动条滚动的时候触发
    lazyLoad(imgs);
}
//图片懒加载结束