本文實例講述了js實作簡潔大方的二級下拉式選單效果程式碼。分享給大家供大家參考。具體如下：
這是一款簡潔大方的二級下拉菜單，菜單的顏色自己根據需要重新定義吧，這裡僅給大家提供一種製作二級菜單的思路，整體效果看上去相當實用，下拉導航菜單也是大家比較常用的。
運作效果截圖如下：
線上示範網址如下：
http://demo.jb51.net/js/2015/js-simple-2level-show-down-menu-codes/
具體程式碼如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>简洁大方的二级下拉菜单</title>
<meta http-equiv="content-type" content="text/html;charset=gb2312">
<style type="text/css">
*{margin:0;padding:0;font-style:normal;font-family:宋体;}
body{text-align:center;font-size:14px;}
#content{margin:0 auto;width:600px;}
#content #nav{background:#006400;height:32px;margin-top:10px;}
#content #nav ul{list-style:none;}
#content #nav ul li{float:left;width:100px;line-height:32px;position:relative;}
#nav div{width:100px;position:absolute;left:0px;padding-bottom:0px;background:#006400;float:left;height:0;overflow:hidden;}
#content #nav li .a{text-decoration:none;color:#00CD00;line-height:32px;display:block;border-right:1px solid #009800;}
#nav div a{text-decoration:none;color:#00CD00;line-height:26px;display:block;}
#nav div a:hover{background:#005400;}
</style>
</head>
<body>
<div id="content">
<div id="nav">
<ul id="supnav">
<li><a href="#" class="a">菜单项1</a>
<div>
<a href="#">菜单测试1</a>
<a href="#">菜单测试1</a>
<a href="#">菜单测试1</a>
</div>
</li>
<li><a href="#" class="a">菜单项2</a>
<div>
<a href="#">菜单测试2</a>
<a href="#">菜单测试2</a>
<a href="#">菜单测试2</a>
</div>
</li>
<li><a href="#" class="a">菜单项3</a>
<div>
<a href="#">菜单测试3</a>
<a href="#">菜单测试3</a>
<a href="#">菜单测试3</a>
<a href="#">菜单测试3</a>
<a href="#">菜单测试3</a>
</div>
</li>
<li><a href="#" class="a">菜单项4</a>
<div>
<a href="#">菜单测试4</a>
<a href="#">菜单测试4</a>
<a href="#">菜单测试4</a>
</div>
</li>
<li><a href="#" class="a">菜单项5</a>
<div>
<a href="#">菜单测试5</a>
<a href="#">菜单测试5</a>
<a href="#">菜单测试5</a>
<a href="#">菜单测试5</a>
</div>
</li>
<li><a href="#" class="a">菜单项6</a>
<div>
<a href="#">菜单测试6</a>
<a href="#">菜单测试6</a>
<a href="#">菜单测试6</a>
</div>
</li>
</ul>
</div>
</div>
<script type="text/javascript">
var supnav=document.getElementById("supnav");
var nav=document.getElementById("nav");
var btns=document.getElementsByTagName("li");
var subnavs=nav.getElementsByTagName("div");
var paddingbottom=20;
var defaultHeight=0;
function drop(obj,ivalue){
var a=obj.offsetHeight;
var speed=(ivalue-obj.offsetHeight)/8;
a+=Math.floor(speed);
obj.style.height=a+"px";
}
window.onload=function(){
for(var i=0;i<btns.length;i++){
btns[i].index=i;
btns[i].onmouseover=function(){
var osubnav=subnavs[this.index];
var sublinks=osubnav.getElementsByTagName("a");
if(osubnav.firstChild.tagName==undefined){
var itarheight=parseInt(osubnav.childNodes[1].offsetHeight)*sublinks.length+paddingbottom;
}else{
var itarheight=parseInt(osubnav.firstChild.offsetHeight)*sublinks.length+paddingbottom;
}
clearInterval(this.itimer);
this.itimer=setInterval(function(){drop(osubnav,itarheight);},30);
}
btns[i].onmouseout=function(){
var osubnav=subnavs[this.index];
clearInterval(this.itimer);
this.itimer=setInterval(function(){drop(osubnav,defaultHeight);},30);
}
}
}
</script>
</body>
</html>希望本文所述對大家的javascript程式設計有所幫助。
