javascriptでプルダウンを変化させる。

javascriptでプルダウンを変化させる。

<form name="sendForm">
<select name="koumoku" size="1" onChange="OnChange()">
<option value="項目">項目
<option value="a">a
<option value="b">b
<option value="c">c
<option value="d">d
</select><br>
<select name="count">
<option value="個数">個数
</select>
</form>
<script language="JavaScript" type="text/javascript">
<!--
function OnChange(){
sel_type_index = document.sendForm.koumoku.selectedIndex;
if(sel_type_index=="2" || sel_type_index=="4"){
document.sendForm.count.options[0] = new Option("1","1");
document.sendForm.count.options[1] = new Option("2","2");
document.sendForm.count.options[2] = new Option("3","3");
document.sendForm.count.options[3] = new Option("4","4");
}else{
document.sendForm.count.options[0] = new Option("2","2");
document.sendForm.count.options[1] = new Option("3","3");
document.sendForm.count.options[2] = new Option("4","4");
}
}
//-->
</script>