function selecttwo(bbb)
{
// var bbb=document.all.selectb.value;
switch(bbb)
{
case 's00' : {document.all.selectb1.style.display='block';break;}
case 's01' : {document.all.selectb2.style.display='';break;}
default : {break;}
}
}记得字符串要加引号，上面是修改后的代码，测试通过
{
// var bbb=document.all.selectb.value;
switch(bbb)
{
case 's00' : {document.all.selectb1.style.display='block';break;}
case 's01' : {document.all.selectb2.style.display='';break;}
default : {break;}
}
}记得字符串要加引号，上面是修改后的代码，测试通过
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>myfind</title>
</head>
<body>
<table width="260" border="0" cellpadding="0" cellspacing="0">
<tr height="20">
<td width="140"><select name="selecta" style="width:90" onChange="document.all.selectb.value=document.all.selecta.options[document.all.selecta.selectedIndex].value">
<option value="000">请选择目录</option>
<option value="s00">概念解释</option>
<option value="s01">常见问题</option>
<option value="s02">图形</option>
</select></td>
<td width="120"><div id="selectb0" style="display:block; width:90; height:20; position:absolute; z-index:2; bottom:inherit; visibility: visible;"><a onMouseOver="javascript:imgfind.src='click1.gif'" onMouseOut="javascript:imgfind.src='click0.gif'" onClick="selecttwo(document.all.selectb.value);"><img src="click0.gif" id="imgfind" border="0"></a>
<div id="selectb1" style="position:absolute;left:0;top:20;width:72px;height:19px;display:none">
<select size="6" onChange="document.all.selectb1.style.display='none'">
<option value="s00">概念解释1</option>
<option value="s00">概念解释2</option>
<option value="s00">概念解释3</option>
</select></div>
</div>
<div id="selectb2" style="position:absolute;width:72px;height:19px;top:35;left:inherit;display:none">
<select size="6" onChange="document.all.selectb2.style.display='none'">
<option value="s00">概念解释4</option>
<option value="s00">概念解释5</option>
<option value="s00">概念解释6</option>
</select></div>
</div>
<input type="text" id="selectb" style="width:90;font-size:12px; border-top-width:0; border-bottom-width:thick; border-left-width:0"></td>
</tr>
</table>
<br>
<input type="button" value="测试按钮" onclick="abc()">
<script language="javascript">
function abc(){alert(document.all.selectb.name)}
function selecttwo(bbb)
{
// var bbb=document.all.selectb.value;
switch(bbb)
{
case 's00' : {document.all.selectb1.style.display='block';break;}
case 's01' : {document.all.selectb2.style.display='';break;}
default : {break;}
}
}
</script>
</body>
</html>