JavaScript判断表单提交时哪个radio按钮被选中的方法

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