原生js可视加载图片、延迟加载、懒加载

<script>
//既视加载
//var oBtn = document.getElementsByTagName('button')[0];
var aImages = document.images;
loadImg(aImages);
window.onscroll = function () {
loadImg(aImages);
};

function loadImg(arr){
for (var i = 0, len = arr.length; i < len; i++) {
// if(arr[i].getBoundingClientRect().top < document.documentElement.clientHeight && !arr[i].isLoad){

//280为图片高度
if(arr[i].getBoundingClientRect().top > -280 && arr[i].getBoundingClientRect().top < document.documentElement.clientHeight && !arr[i].isLoad){
arr[i].isLoad = true;
arr[i].style.cssText = "transition: ''; opacity: 0;"
if(arr[i].dataset){
aftLoadImg(arr[i],arr[i].dataset.original);
}else{
aftLoadImg(arr[i],arr[i].getAttribute("data-original"));
}
(function(i){
setTimeout(function(){
arr[i].style.cssText = "transition: 1s; opacity: 1;"
},16)
})(i);
}
}
}

function aftLoadImg(obj, url) {
var oImg = new Image();
oImg.onload = function(){
obj.src = oImg.src;
}
oImg.src = url;
}
//end既视加载
</script>