代码主体及说明
Javascript部分：
/**
* @函数名:flexScroll
* @功能：滚动超出一定高度,指定元素悬浮
* @两个参数：target_id：目标元素id;topEle:限定滚动高度，超过之后，导航条悬浮
* @调用方式：e.g.：flexScroll('nav',80);
* @author:Kevin 2015/8/14
*/
function flexScroll(target_id,topEle){
window.onscroll=function(){
var scrollTop=document.documentElement.scrollTop || document.body.scrollTop;
var scrollNav=document.getElementById(target_id);
if(scrollTop>topEle){
scrollNav.classList.add('slideDown');
scrollNav.style.position="fixed";
scrollNav.style.top="0";
}else{
scrollNav.classList.remove('slideDown');
scrollNav.style.position="static";
}
}
}
Css动画部分：
.slideDown {
-webkit-animation: slideDown .5s linear;
animation: slideDown .5s linear;
-webkit-animation-fill-mode: both;
-moz-animation-fill-mode: both;
-o-animation-fill-mode: both;
animation-fill-mode: both;
}
@-webkit-keyframes slideDown{
0%{-webkit-transform:translateY(-2rem)}
100%{-webkit-transform:translateY(0)}
}
应用示例
在线演示：http://codepen.io/anon/pen/VLNBgN
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="Generator" content="EditPlus®">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
<title>JavaScript：浮动的导航条</title>
<style type="text/css">
*
{
margin: 0;
padding: 0;
}
.content
{
640px;
height: 1800px;
margin: 0 auto;
background-color: #f5f5f5;
}
.nav
{
line-height: 40px;
640px;
height: 40px;
background-color: #333;
}
.nav li
{
position: relative;
float: left;
25%;
list-style: none;
text-align: center;
color: #fff;
}
.nav li:after
{
content: '';
display: block;
position: absolute;
top: 0;
right: 0;
bottom: 0;
1px;
height: 20px;
margin: auto;
background-color: #999;
}
.nav li:last-child:after
{
display: none;
}
.placehold
{
100%;
height: 80px;
background-color: red;
}
/*动画效果*/
.slideDown
{
-webkit-animation: slideDown .5s linear;
animation: slideDown .5s linear;
-webkit-animation-fill-mode: both;
-moz-animation-fill-mode: both;
-o-animation-fill-mode: both;
animation-fill-mode: both;
}
@-webkit-keyframes slideDown
{
0%
{
-webkit-transform: translateY(-2rem);
}
100%
{
-webkit-transform: translateY(0);
}
}
</style>
</head>
<body>
<div class="content">
<!--占位-->
<div class="placehold"></div>
<!--代码主体-->
<div class="nav" id="nav">
<ul>
<li>足球</li>
<li>篮球</li>
<li>苹果</li>
<li>芒果</li>
</ul>
</div>
</div>
<script>
function flexScroll(target_id,topEle){
window.onscroll=function(){
var scrollTop=document.documentElement.scrollTop || document.body.scrollTop;
var scrollNav=document.getElementById(target_id);
if(scrollTop>topEle){
scrollNav.classList.add('slideDown');
scrollNav.style.position="fixed";
scrollNav.style.top="0";
}else{
scrollNav.classList.remove('slideDown');
scrollNav.style.position="static";
}
}
}
//调用
flexScroll('nav',80);
</script>
</body>
</html>