基于CSS相对定位与JavaScript的下拉菜单实现

<html>
<head>
<title>非定位CSS+Js下拉菜单</title>
<style>
#menu {
  position: absolute;
  font-family: sans-serif;
  font-size: 9pt;
}
#menu li {
  float: left;
  list-style-type: none;
  width: 102px;
  background-color: skyblue;
  border: 1px solid #0066cc;
  text-indent: 0px;
  margin-left: 3px;
}
#menu li a {
  color: blue;
  text-decoration: none;
  width: 100%;
  display: block;
}
#menu li a:hover {
  color: white;
}
#menu li ul {
  background-color: skyblue;
  margin: 0px;
  padding: 0px;
}
#menu li ul li {
  padding: 0px;
  margin: 0px;
  float: none;
  list-style-type: none;
  width: 100px;
  text-indent: 0px;
  border: none;
}
#menu li ul li a{
  color: black;
  text-decoration: none;
}
#menu li ul li a:hover{
  color: black;
  background-color: aqua;
}</style>
<script language="javascript" type="text/javascript">
var t=false,current;
function SetupMenu() {
  if (!document.getElementsByTagName) return;
  items=document.getElementsByTagName("li");
  for (i=0; i<items.length; i++) {
   if (items[i].className != "menu") continue;
   thelink=findChild(items[i],"A");
   thelink.onmouseover=ShowMenu;
   thelink.onmouseout=StartTimer;
   if (ul=findChild(items[i],"UL")) {
     ul.style.display="none";
     for (j=0; j<ul.childNodes.length; j++) {
      ul.childNodes[j].onmouseover=ResetTimer;
      ul.childNodes[j].onmouseout=StartTimer;
     }
   }
  } 
}
function findChild(obj,tag) {
  cn = obj.childNodes;
  for (k=0; k<cn.length; k++) {
   if (cn[k].nodeName==tag) return cn[k];
  }
  return false;
}
function ShowMenu(e) {
  if (!e) var e = window.event;
  thislink = (e.target) ? e.target: e.srcElement;
  ResetTimer();
  if (current) HideMenu(current);
  thislink = thislink.parentNode;
  current=thislink;
  ul = findChild(thislink,"UL");
  if (!ul) return;
  ul.style.display="block";
}
function HideMenu(thelink) {
  ul = findChild(thelink,"UL");
  if (!ul) return;
  ul.style.display="none";
}
function ResetTimer() {
  if (t) window.clearTimeout(t);
}
function StartTimer() {
  t = window.setTimeout("HideMenu(current)",200);
}
window.onload=SetupMenu;
</script>
</head>
<body>
<h1>Menu Test</h1>
<ul id="menu">
<li class="menu"><a href="#">Home</a></li>
<li class="menu"><a href="#">Products</a>
  <ul>
  <li><a href="#">Sub-item 1</a></li>
  <li><a href="#">Sub-item 2</a></li>
  </ul>
</li>
<li class="menu"><a href="#">Support</a>
  <ul>
  <li><a href="#">Sub-item 1</a></li>
  <li><a href="#">Sub-item 2</a></li>
  </ul>
</li>
<li class="menu"><a href="#">Employment</a>
  <ul>
  <li><a href="#">Sub-item 1</a></li>
  <li><a href="#">Sub-item 2</a></li>
  </ul>
</li>
<li class="menu"><a href="#">Contact Us</a>
  <ul>
  <li><a href="#">Sub-item 1</a></li>
  <li><a href="#">Sub-item 2</a></li>
  </ul>
</li>
</ul>
</body>
</html>