js实现导航菜单鼠标感应弹出显示特效，挺漂亮的js二级导航菜单弹出效果，用js+css制作，可根据自己的需求来自己修改。
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<title>不错的js二级导航菜单弹出特效_武鸣人</title>
<script type=text/javascript>
/**
*菜单的构造,需要绑定到onload
*/
startList = function() {
if (document.all&&document.getElementById) {
dropmenuRoot = document.getElementById("dropmenu");
for (i=0; i<dropmenuRoot.childNodes.length; i++) {
node = dropmenuRoot.childNodes[i];
if (node.nodeName=="LI") {
node.onmouseover=function() {
this.className+=" over";
//开始灌水
for(j=0;j<this.childNodes.length;j++){
if (this.childNodes[j].nodeName=="UL"){
if (this.childNodes[j].childNodes[0].nodeName=="LI"){
if (this.offsetLeft+this.childNodes[j].childNodes.length*this.childNodes[j].childNodes[0].offsetWidth-dropmenuRoot.offsetLeft>dropmenuRoot.offsetWidth){
var len=this.childNodes[j].childNodes.length*this.childNodes[j].childNodes[0].offsetWidth; //菜单的长度
(len>dropmenuRoot.offsetWidth) ? this.childNodes[j].style.width=776+"px" : this.childNodes[j].style.width=len+"px"; //给ul设置宽度 如果子菜单比较多，大于容器的宽度，那么ul的宽度就是容器的宽度
len =this.offsetLeft+len-dropmenuRoot.offsetLeft-dropmenuRoot.offsetWidth;
(len>this.offsetLeft-dropmenuRoot.offsetLeft) ? this.childNodes[j].style.marginLeft=-(this.offsetLeft-dropmenuRoot.offsetLeft) : this.childNodes[j].style.marginLeft=-len+"px";
}
}
}
}//武鸣人网站https://www.wuming.ren 网站很好记住，wuming.ren(武鸣拼音.ren域名后缀)
}
//灌水完毕
node.onmouseout=function() {
this.className=this.className.replace(" over", "");
}
}//武鸣人网站https://www.wuming.ren 网站很好记住，wuming.ren(武鸣拼音.ren域名后缀)
}
}
}//武鸣人网站https://www.wuming.ren 网站很好记住，wuming.ren(武鸣拼音.ren域名后缀)
window.onload=startList;
</script>
</head>
<style type="text/css">
body { font: normal 11px verdana; background: #45b97c; position:absolute }
ul { margin: 0; padding: 0; }
li { list-style-position: outside; list-style: none;}
a { text-decoration: none; color: #666;}
ul#dropmenu,ul#dropmenu ul{
margin: 0 auto;
text-align: left;
padding: 0;
list-style: none;
z-index: 99;
}
ul#dropmenu {
width: 774px;
display: block;
height: 24px;
clear: both;
border: 1px solid #ccc;
text-align: center;
background: #fff;
}
ul#dropmenu li {
position: relative;
z-index: 999;
float: left;
}
ul#dropmenu ul li{
float: left;
display: block;
}
ul#dropmenu ul {
/*width: 122px;
w\idth: 120px;*/
height: auto;
position: absolute;
text-align: left;
left: 0px;
display: none;
border: solid 1px #ccc;
}
/*当鼠标在子菜单和父菜单上时，父菜单的样式*/
ul#dropmenu li.over a,ul#dropmenu li:hover a{
border-color: #ccc;
background: #c00;
color: #fff;
}
/*将子菜单的样式清除*/
ul#dropmenu li.over ul a,ul#dropmenu li:hover ul a{
font-weight: normal;
color: #666;
background: #fff;;
}
/*子菜单的hover样式*/
ul#dropmenu li.over ul a:hover,ul#dropmenu li:hover ul a:hover{
font-weight: normal;
color: #cc0000;
font-weight: bold;
background: #f6f6f6;
}
/* Styles for Menu Items */
ul#dropmenu a {
display: block;
padding: 0 0 0 10px;
width: 106px;
w\idth: 96px;
color: #666;
line-height: 24px;
}
ul#dropmenu ul li{
width: 110px;
border: 0;
}
/* End */
ul#dropmenu ul a {
FILTER: progid:DXImageTransform.Microsoft.Alpha(opacity=70); /* 透明 */
padding: 2px 0px 2px 10px;
border: 0;
width: 120px;
w\idth: 110px;/* Sub Menu Styles */
}
ul#dropmenu li:hover ul,ul#dropmenu li.over ul {
display: block; /* The magic */
}
</style>
<body>
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