jQuery如何判断滚动条是否到了底部？
判断滚动条到底部，需要用到DOM的三个属性值，即scrollTop、clientHeight、scrollHeight。
scrollTop为滚动条在Y轴上的滚动距离。
clientHeight为内容可视区域的高度。
scrollHeight为内容可视区域的高度加上溢出（滚动）的距离。
从这个三个属性的介绍就可以看出来，滚动条到底部的条件即为scrollTop + clientHeight == scrollHeight。
废话不多少说，赶紧上代码（兼容不同的浏览器）。
lazyload.js
//滚动条在Y轴上的滚动距离
function getScrollTop(){
var scrollTop = 0, bodyScrollTop = 0, documentScrollTop = 0;
if(document.body){
bodyScrollTop = document.body.scrollTop;
}
if(document.documentElement){
documentScrollTop = document.documentElement.scrollTop;
}
scrollTop = (bodyScrollTop - documentScrollTop > 0) ? bodyScrollTop : documentScrollTop;
return scrollTop;
}
//文档的总高度
function getScrollHeight(){
var scrollHeight = 0, bodyScrollHeight = 0, documentScrollHeight = 0;
if(document.body){
bodyScrollHeight = document.body.scrollHeight;
}
if(document.documentElement){
documentScrollHeight = document.documentElement.scrollHeight;
}
scrollHeight = (bodyScrollHeight - documentScrollHeight > 0) ? bodyScrollHeight : documentScrollHeight;
return scrollHeight;
}
//浏览器视口的高度
function getWindowHeight(){
var windowHeight = 0;
if(document.compatMode == "CSS1Compat"){
windowHeight = document.documentElement.clientHeight;
}else{
windowHeight = document.body.clientHeight;
}
return windowHeight;
}
window.onscroll = function(){
if(getScrollTop() + getWindowHeight() == getScrollHeight()){
alert("you are in the bottom!");
}
};
lazyload-jQuery.js
$(window).scroll(function(){
var scrollTop = $(this).scrollTop();
var scrollHeight = $(document).height();
var windowHeight = $(this).height();
if(scrollTop + windowHeight == scrollHeight){
alert("you are in the bottom");
}
});
lazyLoad.html
<!doctype html>
<html lang="en" style="height:900px;">
<head>
<meta charset="UTF-8">
<meta name="Author" content="forever">
<link rel="stylesheet" href="css/lazyload.css" />
<script type="text/javascript" src="js/jquery-1.7.2.min.js"></script>
<title>lazyLoad</title>
<script type="text/javascript">
$(function(){
var $ul=$("#lazyLoadWrap").find("ul");
$(window).scroll(function(){
var scrollTop = $(this).scrollTop();
var scrollHeight = $(document).height();
var windowHeight = $(this).height();
if(scrollTop + windowHeight == scrollHeight){
for(var i=0;i<6;i++){
$ul.append("<li>Hello</li>");
}
}
});
});
</script>
</head>
<body>
<div id="lazyLoadWrap">
<ul>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li></li>
<li>12</li>
</ul>
</div>
</body>
</html>
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