主要是两个select在onChange时的两个方法，
删除一个select框中的项
document.all("test").options.remove(i)
增加一个select框中的项
document.all("test").options.add(new Option("选项","值"));
selectedIndex表示该选框当前选的值的序号，从0~length-1表示,可以指定selectedIndex的值，既可指定其对应的选项.
源程序
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<style type="text/css">
body{font-family:Courier New, Courier}
select{font-size:8pt;font-family:Courier New, Courier}
input{font-size:8pt;font-family:Courier New, Courier}
</style>
<SCRIPT LANGUAGE="JavaScript">
<!--
var Name=new Array(3);
var Value=new Array(3);
Name[1]=new Array("Zosatapo1","Zosatapo2","Zosatapo3","Zosatapo4");
Name[2]=new Array("Reic Yang1","Reic Yang2","Reic Yang3","Reic Yang4");
<HEAD>
<TITLE> New Document </TITLE>
<META NAME="Generator" CONTENT="EditPlus">
<META NAME="Author" CONTENT="">
<META NAME="Keywords" CONTENT="">
<META NAME="Description" CONTENT="">
<style type="text/css">
body{font-family:Courier New, Courier}
select{font-size:8pt;font-family:Courier New, Courier}
input{font-size:8pt;font-family:Courier New, Courier}
</style>
<SCRIPT LANGUAGE="JavaScript">
<!--
var Name=new Array(3);
var Value=new Array(3);
Name[1]=new Array("Zosatapo1","Zosatapo2","Zosatapo3","Zosatapo4");
Name[2]=new Array("Reic Yang1","Reic Yang2","Reic Yang3","Reic Yang4");
function change()
{
selIndex=document.all("test").selectedIndex;
if(document.all("test").selectedIndex==0)
return;
{
selIndex=document.all("test").selectedIndex;
if(document.all("test").selectedIndex==0)
return;
for(i=document.all("test").options.length-1;i>-1;i--)
{
document.all("test").options.remove(i);
}
{
document.all("test").options.remove(i);
}
for(i=0;i<Name[selIndex].length;i++)
{
document.all("test").options.add(new Option(Name[selIndex][i],"name"+i));
}
{
document.all("test").options.add(new Option(Name[selIndex][i],"name"+i));
}
}
function changeEx(){
for(i=document.all("sub").options.length;i>0;i--)
{
document.all("sub").options.remove(i-1);
}
{
document.all("sub").options.remove(i-1);
}
if(document.all("main").selectedIndex==0){
document.all("sub").options.add(new Option("==========","-1"));
return;}
document.all("sub").options.add(new Option("==========","-1"));
return;}
selIndex=document.all("main").selectedIndex;
for(i=0;i<Name[selIndex].length;i++)
{
document.all("sub").options.add(new Option(Name[selIndex][i],"name"+i));
}
{
document.all("sub").options.add(new Option(Name[selIndex][i],"name"+i));
}
}
function reset(){
for(i=document.all("test").options.length-1;i>-1;i--)
{
document.all("test").options.remove(i);
}
for(i=document.all("test").options.length-1;i>-1;i--)
{
document.all("test").options.remove(i);
}
document.all("test").options.add(new Option("==========","-1"));
document.all("test").options.add(new Option("Zosatapo","1"));
document.all("test").options.add(new Option("Reic Yang","2"));
}
function display(object){
alert(object.options[object.selectedIndex].text+" "+object.options[object.selectedIndex].value);
}
//-->
</SCRIPT>
</HEAD>
alert(object.options[object.selectedIndex].text+" "+object.options[object.selectedIndex].value);
}
//-->
</SCRIPT>
</HEAD>
<BODY BGCOLOR="#FFFFFF">
First Sample:<br><font color="blue">All items will change After you Selected!</font><br>
<SELECT id="test" onchange="change();">
<option value="-1" selected>==========
<option value="1">Zosatapo
<option value="2">Reic Yang
</SELECT><input name="Reset Select" type="button" value="Reset Select" onclick="reset();" ><br><br>
First Sample:<br><font color="blue">All items will change After you Selected!</font><br>
<SELECT id="test" onchange="change();">
<option value="-1" selected>==========
<option value="1">Zosatapo
<option value="2">Reic Yang
</SELECT><input name="Reset Select" type="button" value="Reset Select" onclick="reset();" ><br><br>
Second Sample:<br><font color="blue">You selected Item in Main Select will change the Sub select Content!</font><br>
Main Select:<SELECT id="main" onchange="changeEx();">
<option value="-1" selected>==========
<option value="1">Zosatapo
<option value="2">Reic Yang
</SELECT>
Main Select:<SELECT id="main" onchange="changeEx();">
<option value="-1" selected>==========
<option value="1">Zosatapo
<option value="2">Reic Yang
</SELECT>
Sub Select:<SELECT id="sub" onchange="display(this);">
<option value="-1" selected>==========
</SELECT><br><br>
</BODY>
</HTML>
<option value="-1" selected>==========
</SELECT><br><br>
</BODY>
</HTML>