<script language=vbscript>
dim i
i=0
Dim a
Sub cc()
Set a=document.createElement("option")
a.innerText="a" & i
a.value="a" & i
document.f.demo.appendChild a
i=i+1
End Sub
</script>
<form name=f>
<select name=demo></select>
<input type=button value=ok onclick="vbscript:cc">
</form>