자바스크립트 radio버튼 체크 유효성 검사

<script language="JavaScript">
<!--
function onsubmit() {

     var frm = document.all;

 

     var radio_num = document.all.radio.length;

     var chk_i = 0;

   

     for(var i=0; i<radio_num; i++){

          if(frm.radio[i].checked == true){

                 chk_i++;

                 break;

          }

     }

 

     if(chk_i <= 0){

          alert("선택해 주세요.");

          return;

     }

} 
//-->
</script>

 

<input type="radio" name="radio" value="1">

<input type="radio" name="radio" value="2">

<input type="radio" name="radio" value="3">

<input type="radio" name="radio" value="4">

<input type="radio" name="radio" value="5">

 

<input type="button" onClick="onsubmit();" value="전송">