求一JS效果!

Question

<script>
function alertTest()
{
var flag;
if (document.all.radio_1[0].checked)
flag=false;
if (document.all.radio_1[1].checked) 
flag=true;
document.all.textfield.readOnly=flag;
document.all.radio[0].disabled=flag;
document.all.radio[1].disabled=flag;}
</script>
<table width="500" border="1" cellspacing="0" cellpadding="0">
    <tr> 
      <td width="136"><input type="radio" name="radio_1" value="1" onClick="alertTest()">
        a
<input type="radio" name="radio_1" value="2" onClick="alertTest()">
        b</td>
      <td width="111" height="18"><input name="textfield" type="text" size="10"></td>
      <td width="245"><input type="radio" name="radio" value="1">
        c 
        <input type="radio" name="radio" value="1">
        d</td>
    </tr>
  </table>