let imgs = document.getElementsByTagName("img");
let n = 0

lazyload()

//节流函数
function throttle(handleEvent,time){
    let timer
    return function(...args){
        if(timer){
            timer = setTimeout(() => {
                timer = null
                handleEvent.apply(this,args)
            }, time);
        }
    }
}
function lazyload(){
    let seeHight = window.innerHeight
    let scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
    for(let i = n; i < imgs.length; i++){
        if(imgs[i].offsetTop < seeHight + scrollTop){
            if(imgs[i].getAttribute('src') == 'loading.gif'){
                imgs[i].src = imgs[i].getAttribute('data-src');
            }
            n = i + 1;
        }
    }
}

window.addEventListener('scroll',throttle())