How to find radio button selection when a form is submitted?

<script type=”text/javascript”>
function findButton() {
var myForm = document.forms.animalForm;
var i;
for(i=0;i<myForm.marsupial.length; i++) {
if(myForm.marsupial[i].checked) {
break;}
}

alert(“You selected ”"+myForm.marsupial[i].value+“”.”);}

</script>

<form name=”animalForm” action=”">
 <input type=”radio” name=”marsupial” value=”kangaroo” />Kangaroo<br />
 <input type=”radio” name=”marsupial” value=”Opossum” />Opossum<br />
 <input type=”radio” name=”marsupial” value=”Tasmanian Tiger” />Tasmanian Tiger
 <input type=”button” name=”GO” value=”GO” onclick=”findButton()” />
...