Javascript:浮动的导航条

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>