怎样获得被选中的radio的值

Question

<script>
function f1()
{
var obj=document.getElementsByName("rad");
for(var i=0;i<obj.length;i++)
  {
    if(obj[i].checked)
     {
      alert(obj[i].value)
     }
  }}
</script>
<input type="button" onclick=f1()>
<input type="radio" id="radio1" name="rad" value="sss1">
<input type="radio" id=Radio2 name="rad"  value="sss2">
<input type="radio" id=Radio3 name="rad" value="sss3">
<input type="radio" id=Radio4 name="rad" value="sss4">

Answer 1

<input type="radio" name="radio1" value=1>
<input type="radio" name="radio1" value=2>
<input type="radio" name="radio1" value=3>
<input type="radio" name="radio1" value=4>
<a href="javascript:fn();">查看</a>function fn(){
    alert(getRadioValue("radio1"));
}
function getRadioValue(raidoName){
    var raidos = document.getElementsByName(raidoName);
    for(var i=0;i<radios.length;i++){
        if(radios[i].checked) return radios[i].value;
    }
    return null;
}