下拉列表disabled属性为什么不起作用？？请高手指点！！！！！
<html>
<script language= "JavaScript ">
function selectdu()
{
alert( "choise is ");
var strSel = document.branchForm.branchLevel.options[document.branchForm.branchLevel.selectedIndex].text;
alert(strSel);
if(strSel == "国家 ")
{
nation.disabled = true;
province.disabled = true;
organizaiton.disabled = true;
}
else if(strSel == "省(州) ")
{
nation.disabled = false;
province.disabled = true;
organizaiton.disabled = true;
}
else if(strSel == "地、市、厅 ")
{
nation.disabled = false;
province.disabled = false;
organizaiton.disabled = true;
}
else
{
nation.disabled = false;
province.disabled = false;
organizaiton.disabled = false;
}
}
</script>
<BODY >
<form name= "branchForm " method= "post ">
<select name= "branchLevel " property= "ilevel " OnChange= "selectdu() " size= "1 " style= "width: 210px; height: 20 " >
<option value= " "/>
<option value=17> 国家 </option>
<option value=18> 省(州) </option>
<option value=19> 地、市、厅 </option>
<option value=20> 院(处) </option>
</select>
<select name= "nation " style= "width:210px; height: 20 "> </select>
<select name= "province " style= "width:210px; height: 20 "> </select>
<select name= "organizaiton " style= "width:210px; height: 20 "> </select>
</form>
</BODY>
</html>
------解决方案--------------------
<script language= "JavaScript ">
function selectdu()
{
var obj = document.branchForm;
var strSel = obj.branchLevel.options[document.branchForm.branchLevel.selectedIndex].text;
if(strSel == "国家 ")
{
obj.nation.disabled = true;
obj.province.disabled = true;
obj.organizaiton.disabled = true;
}
else if(strSel == "省(州) ")
{
obj.nation.disabled = false;
obj.province.disabled = true;
obj.organizaiton.disabled = true;
}
else if(strSel == "地、市、厅 ")
{
obj.nation.disabled = false;
obj.province.disabled = false;
obj.organizaiton.disabled = true;
}
else
{
obj.nation.disabled = false;
obj.province.disabled = false;
obj.organizaiton.disabled = false;
}
}
</script>
