可输入的下拉框

应需求，要写一个可以输入的下拉框。

先贴代码：

<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<script language="javascript">
    function changeF()
    {
       document.getElementById('makeupCo').value=
       document.getElementById('makeupCoSe').options[document.getElementById('makeupCoSe').selectedIndex].value;
    }
    
</script>

<span style="position:absolute;border:1pt solid #c1c1c1;overflow:hidden;width:188px;
    height:19px;clip:rect(-1px 190px 190px 170px);">

<select name="makeupCoSe" id="makeupCoSe" style="width:190px;height:20px;margin:-2px;" onChange="changeF();">
    <option  value='50'>50</option>
    <option  value='100'>100</option>
    <option  value='200'>200</option>
    <option  value='300'>300</option>
    <option  value='500'>500</option>
    <option  value='1000'>1000</option>
</select>
</span>
<form method="post" action="pay.php"> 
<span style="position:absolute;border-top:1pt solid #c1c1c1;border-left:1pt 
    solid #c1c1c1;border-bottom:1pt solid #c1c1c1;width:170px;height:19px;">
    <input type="text" name="makeupCo" id="makeupCo" value="请选择或输入" style="width:170px;height:15px;border:0pt;" onfocus="if (value==defaultValue) value=''" onblur="if(!value) value=defaultValue">
</span>
<input style="margin-top:50px;" type="submit" value="提交">
</form>