htm页面：
<script src="js/admin_js.js" language="javascript"></script>
<script language=JavaScript>
document.onclick = clickList;
</script>
<table width="216" border="0" cellpadding="0" cellspacing="0">
<tr>
<td height="533" background="images/left.jpg" align="center" valign="top">
<div id=div0 style="width:216; position:relative">
<label id=div0 style="cursor: hand; background:url(images/left_main.jpg); width:216; height:31; text-align:center; color:#f0f0f0; padding-top:12px">部门管理</span></label>
</div>
<div id=div0other style="display:None; width:216">
<label style="background:url(images/left_part.jpg); width:216; height:24; padding-top:8px"><a href="bmgl/show_depart.php" target="mainFrame">
查看部门</a></label>
<label style="background:url(images/left_part.jpg); width:216; height:24; padding-top:8px"><a href="bmgl/add_depart.php" target="mainFrame">添加部门</a></label>
</div>
javascript:admin_js.js
function clickList() {
var targetId, srcElement, targetElement;
/*event对象指当前触发的事件对象, window.event.srcElement是指触发事件的对象(event:得到或设置触发事件的对象，event.srcElement:指向触发事件的元素)。比如上面htm页面设定document.onclick = clickList;这时所有页面点击的事件都交给 clickList处理，在 clickList函数里写 srcElement = window.event.srcElement，知道用户是点击了什么地方，做相应处理。*/
srcElement = window.event.srcElement;
/*srcElement.className:得到触发事件对象的样式名称，对应上面htm页面class=active */
if (srcElement.className == "active") {
/*在目标ID后加上"other"字符串，此例即为：div0other,代表子菜单*/
targetId = srcElement.id + "other";
targetElement = document.all(targetId);//当点击母菜单"部门管理后"，显示子菜单"查看部门"、"添加部门"
/*下面，默认子菜单样式为不可见*/
if (targetElement.style.display == "none") {
targetElement.style.display = "";
} else {
targetElement.style.display = "none";
}
}
}