Show alert when radio button value is selected

<script type="text/javascript">
function radio_form(){
   var selectvalue = $('input[name=choice]:checked', '#radio_form').val();

if(selectvalue == "V1"){
   alert('Value 1');
   return true;
}else if(selectvalue == "V2"){
   alert('Value 2');
   return true;
}else if(selectvalue == 'V3'){
   alert('Value 3');
   return true;
}else if(selectvalue == 'V4'){
   alert('Value 4');
   return true;
}
return false;
};
</script>

<form id="radio_form">
  <input type="radio" onclick="radio_form()"  name="choice" value="V1"> 
  <input type="radio" onclick="radio_form()" name="choice" value="V2"> 
  <input type="radio" onclick="radio_form()" name="choice" value="V3">
  <input type="radio" onclick="radio_form()" name="choice" value="V4"> 
</form>

I am trying to show an alert when a radio value is selected...however this approach doesn't seem to work.

Am I doing something wrong?