效果：左侧导航栏，点击展开，显示子菜单。再次点击，菜单折叠。
代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=gb2312" /><title>柠檬酒店</title><style>/*设置导航每个主菜单的样式*/.main_nav{display:block;width:200px;padding:10px; font-weight:bold; background-color:#BADFF2;}li{list-style:none;}#globalNav {position:absolute;top:3px;left:2px;}/*导航中每个子菜单的样式*/#globalNav ul li a{margin:auto 10px;display:block;width:140px; color:#fff;font-weight:bold;text-decoration:none;}#globalNav li ul li a{background:#6DBBE1;}#globalNav li ul li a:hover{background:#BCF2F0;<!--鼠标经过的颜色--> }</style><script type="text/javascript" >function initTree(t) {var tree=document.getElementById(t);//生成树tree.style.display="none";//设置样式为隐藏形式，不显示var lis=tree.getElementsByTagName("li");for(var i=0;i<lis.length;i++) { //取出主要的导航栏lis[i].id="li"+i;var uls=lis[i].getElementsByTagName("ul"); //子导航栏if(uls.length!=0) {uls[0].id="ul"+i;uls[0].style.display="none";var as=lis[i].getElementsByTagName("a"); //子导航栏的内容as[0].id="a"+i;as[0].className="folder";as[0].href="#this";as[0].tget=uls[0];as[0].onclick=function() {openTag(this,this.tget);}}}tree.style.display="block";}function openTag(a,t) {if(t.style.display=="block") { //点击一些展开，再点击一下折叠t.style.display="none";a.className="folder";} else {t.style.display="block";a.className="";}}window.onload=function() {initTree("globalNav");}</script></head><body id="index"><ul id="globalNav"><li class="main_nav"><a href="#">房间信息</a><ul><li><a href="nullroom.php" target="mainFrame">空房</a></li><li><a href="room.php" target="mainFrame">所有房间</a></li><li><a href="orderroom.php" target="mainFrame">被订房间</a></li><li><a href="register/room.html" target="mainFrame">录入房间信息</a></li></ul></li><li class="main_nav"><a href="#">房客信息</a><ul><li><a href="register/custom.html" target="mainFrame">录入房客信息</a></li><li><a href="custom_info.php" target="mainFrame">客史档案</a></li></ul></li><li class="main_nav"><a href="#">订单</a><ul><li><a href="register/order.html" target="mainFrame">录入订单信息</a></li><li><a href="order.php" target="mainFrame">查看订单</a></li></ul></li><li class="main_nav"><a href="#">会员</a><ul><li><a href="register/member.html" target="mainFrame">录入会员信息</a></li><li><a href="member.php" target="mainFrame">查看会员信息</a></li></ul></li><li class="main_nav"><a href="#">财务</a><ul><li><a href="register/cash.html" target="mainFrame">录入财务信息</a></li><li><a href="cash.php" target="mainFrame">查看财务信息 </a></li></ul></li><li class="main_nav"><a href="login/login.html" target="_parent">退出</a></li></ul></body></html>
