JavaScript下拉菜单
一篇 [url=http://www.helloxudan.net/2007/11/09/inquiry-pure-css-drop-down-menu.html]CSS 下拉菜单[/url]，其中完全只使用 CSS 实现了导航条鼠标悬停下拉菜单的效果（[url=http://www.helloxudan.net/css/drop-down-menu/test.html]演示地址[/url]）。但是只用 CSS 实现起来比较麻烦，代码较多，而且为了浏览器的兼容性不得不使用了两个 CSS 文件，所以我把它叫做“探究”，实用性并不强。最近我从 blog 的流量统计中发现，很多网友通过搜索“JS 下拉菜单”关键字访问到了我的那篇文章。不过很遗憾，那篇文章和JavaScript 一点关系都没有，有误导网友之嫌。所以，昨天我花了一点时间把原来的代码做了一点修改，搞了一个 JS 版下拉菜单。其实用JS 实现下拉菜单比 CSS 简单多了，因为各个浏览器之间对 JS 支持的差异相比 CSS来说要小一些，不需要花那么多心思用在对付浏览器上。如果 HTML 的结构良好，只需要很少的 JS代码即可实现，而且可以实现多级下拉菜单的效果（我的示例中给出了二级下拉菜单，可以根据需要按照原来的 HTML 结构逐级添加）。
[b][url=http://www.helloxudan.net/js/drop-down-menu.html]演示地址[/url][/b]
页面源代码：
[color=Olive]<[/color][color=Gray]![/color][color=#008b]DOCTYPE[/color]
[color=#008b]html[/color]
[color=#008b]PUBLIC[/color]
[color=#8b00]"[/color][color=Red]-//W3C//DTD XHTML 1.0 Strict//EN[/color][color=#8b00]"[/color]
[color=#8b00]"[/color][color=Red]http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]html[/color]
[color=#008b]xmlns[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]http://www.w3.org/1999/xhtml[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]head[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]meta[/color]
[color=#008b]http-equiv[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]Content-Type[/color][color=#8b00]"[/color]
[color=#008b]content[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]text/html; charset=utf-8[/color][color=#8b00]"[/color]
[color=Olive]/>[/color]
[color=Olive]<[/color][color=Green]title[/color][color=Olive]>[/color][color=Gray]JavaScript下拉菜单[/color][color=Olive]</[/color][color=Green]title[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]style[/color]
[color=#008b]type[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]text/css[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]
* {
padding:0;
margin:0;
}
body {
font-family:verdana, sans-serif;
font-size:small;
}
#navigation, #navigation li ul {
list-style-type:none;
}
#navigation {
margin:20px;
}
#navigation li {
float:left;
text-align:center;
position:relative;
}
#navigation li a:link, #navigation li a:visited {
display:block;
text-decoration:none;
color:#000;
width:120px;
height:40px;
line-height:40px;
border:1px solid #fff;
border-width:1px 1px 0 0;
background:#c5dbf2;
padding-left:10px;
}
#navigation li a:hover {
color:#fff;
background:#2687eb;
}
#navigation li ul li a:hover {
color:#fff;
background:#6b839c;
}
#navigation li ul {
display:none;
position:absolute;
top:40px;
left:0;
margin-top:1px;
width:120px;
}
#navigation li ul li ul {
display:none;
position:absolute;
top:0px;
left:130px;
margin-top:0;
margin-left:1px;
width:120px;
}
[/color][color=Olive]</[/color][color=Green]style[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]script[/color]
[color=#008b]type[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]text/javascript[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]
function displaySubMenu(li) {
var subMenu = li.getElementsByTagName("ul")[0];
subMenu.style.display = "block";
}
function hideSubMenu(li) {
var subMenu = li.getElementsByTagName("ul")[0];
subMenu.style.display = "none";
}
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[color=Olive]</[/color][color=Green]head[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]body[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]ul[/color]
[color=#008b]id[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]navigation[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color]
[color=#008b]onmouseover[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]displaySubMenu(this)[/color][color=#8b00]"[/color]
[color=#008b]onmouseout[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]hideSubMenu(this)[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]a[/color]
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[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目1->菜单3[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目1->菜单4[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]ul[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color]
[color=#008b]onmouseover[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]displaySubMenu(this)[/color][color=#8b00]"[/color]
[color=#008b]onmouseout[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]hideSubMenu(this)[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目2[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]ul[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目2->菜单1[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目2->菜单2[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目2->菜单3[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目2->菜单4[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目2->菜单5[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]ul[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color]
[color=#008b]onmouseover[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]displaySubMenu(this)[/color][color=#8b00]"[/color]
[color=#008b]onmouseout[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]hideSubMenu(this)[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目3[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]ul[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color]
[color=#008b]onmouseover[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]displaySubMenu(this)[/color][color=#8b00]"[/color]
[color=#008b]onmouseout[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]hideSubMenu(this)[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目3->菜单1[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]ul[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]菜单1->子菜单1[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]菜单1->子菜单2[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]菜单1->子菜单3[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]菜单1->子菜单4[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]ul[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目3->菜单2[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color]
[color=#008b]onmouseover[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]displaySubMenu(this)[/color][color=#8b00]"[/color]
[color=#008b]onmouseout[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]hideSubMenu(this)[/color][color=#8b00]"[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]栏目3->菜单3[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]ul[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]菜单3->子菜单1[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]菜单3->子菜单2[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]<[/color][color=Green]li[/color][color=Olive]><[/color][color=Green]a[/color]
[color=#008b]href[/color][color=Gray]=[/color][color=#8b00]"[/color][color=Red]#[/color][color=#8b00]"[/color][color=Olive]>[/color][color=Gray]菜单3->子菜单3[/color][color=Olive]</[/color][color=Green]a[/color][color=Olive]></[/color][color=Green]li[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]ul[/color][color=Olive]>[/color]
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[color=Olive]</[/color][color=Green]body[/color][color=Olive]>[/color]
[color=Olive]</[/color][color=Green]html[/color][color=Olive]>[/color]
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