判断单选框是否选择的JavaScript代码

<form name="form1" method="GET" action="save.php">
<tr>
<td><input type="radio" name="radioGroup" value="1"></td>
<td><input type="button" name="btnChk" value="Check" onClick='javascript: getRadioChk()'></td>
</tr>
..........
</from>
<script language="javascript">
function getRadioChk() {
var radio=document.form1.radioGroup
if(radio.length){
  for (i=0; i<(radio.length); i++) {
   if (radio.checked) {
    alert('ok');
    break;
   }
  }
}
else{
  if(radio.checked){alert('ok');}
}
}
</script>