延迟加载：
obj.offsetTop < 可视区高度 + 滚动距离;
obj.offsetTop < document.documentElement.clientHeight +
(document.documentElement.scrollTop || document.body.scrollTop);
<html lang="en">
<head>
<meta charset="UTF-8">
<title></title>
<style>
*{margin:0;padding:0;list-style:none;}
ul{
width: 200px;
border:1px solid #000;
float:left;
margin:10px;
}
li{
width: 180px;
height: 200px;
background: red;
margin:10px;
}
</style>
<script>
function rnd(n,m){return parseInt(Math.random()*(m-n)) + n;}
window.onload = function(){
var aUl = document.getElementsByTagName('ul');
function createLI(){
var oLi = document.createElement('li');
oLi.style.height = rnd(100,500) + 'px';
oLi.style.background = 'rgb('+rnd(0,256)+','+rnd(0,256)+','+rnd(0,256)+')';
return oLi;
}
function createLI20(){
for(var i = 0; i < 20; i++){
var oLi = createLI();
var arrUl = [];
for(var j = 0; j<aUl.length; j++){
arrUl.push(aUl[j]);
}
arrUl.sort(function(n1,n2){
return n1.offsetHeight - n2.offsetHeight;
});
arrUl[0].appendChild(oLi)
}
}
createLI20();
window.onscroll = function(){
var clientH = document.documentElement.clientHeight;
var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
var clientBottom = clientH + scrollTop;
//页面内容高度
var pageHeight = document.documentElement.scrollHeight;
document.title = pageHeight + ',' + clientBottom;
if(pageHeight <= clientBottom){
// alert(pageHeight + ',' + clientBottom);
createLI20();
}
};
};
</script>
</head>
<body>
<ul></ul>
<ul></ul>
<ul></ul>
</body>
</html>
预加载-图片：
自己偷偷地加载
Image对象：
//创建一个新的Image对象
var img = new Image();
img.src img....
var img = new Image();
img.src = 'img/bbb1.jpg';
img.onload = function(){
alert('加载完成！');
};
img.onerror = function(){
alert('失败了！');
};
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