onclick function for adding the amounts by javascript

As I am currently working with my project for addcart. I have written the javascript query for radio button can any one check this either my query is wrong or right?

JavaScript:

function get_radio_value()
{
for (var i=0; i < document."make_payment_frm".rmr.length; i++)
   {
   if (document."make_payment_frm".rmr[i].checked)
      {
      var rad_val = document."make_payment_frm".rmr[i].value;
      }
   }
}

HTML:

<input name="rmr" id="rmr" type="radio" value="3"  onclick="get_radio_value()">
<input name="rmr" id="rmr" type="radio" value="5"  onclick="get_radio_value()">
<input name="rmr" id="rmr" type="radio" value="10"  onclick="get_radio_value()">

Can any one give me the correct code? If I click those buttons that amount should be added with 开发者_StackOverflowaddcart amount. For example: if my addcart amount is 27£ then I choose 2nd radio button finaly it should be display like a 32£.

Thanks in advance.

Your syntax is off, it should be document.make_payment_frm, not quotes in there (that's for bracket notation, e.g. document["make_payment_frm"]). Also, IDs shouldn't be repeated, your inputs should just be:

<input name="rmr" type="radio" value="3"  onclick="get_radio_value()" />
<input name="rmr" type="radio" value="5"  onclick="get_radio_value()" />
<input name="rmr" type="radio" value="10"  onclick="get_radio_value()" />

Then matching script to get the value:

function get_radio_value() {
  var rad_val = 0;
  for (var i=0; i < document.make_payment_frm.rmr.length; i++) {
    if (document.make_payment_frm.rmr[i].checked) {
       rad_val = document.make_payment_frm.rmr[i].value;
       break;
    }
  }
  //use rad_val here to add to whatever
}

You can test it out here.

But since you tagged this jQuery, why not take full advantage of it? Remove those onclick handlers and add a click or change handler, like this:

$(function() {
  $("input[name='rmr']").change(function() {
    var val = +$(this).val();
    //use val, it's a number ready to add to
  });
});

You can test that version here.