<form action="#" method="post" class="demoForm" id="demoForm">

    <fieldset>

        <legend>Demo: Get Value of Selected</legend>

    <p>Select a shipping method:</p>

    <p>

        <label><input type="radio" name="ship" value="A" checked /> A</label>

        <label><input type="radio" name="ship" value="B" />B</label>

        <label><input type="radio" name="ship" value="C" /> C</label>

        <label><input type="radio" name="ship" value="D" /> D</label>

    </p>

    <p><button type="button" name="getVal">Get Value of Selected</button></p>

    </fieldset>

</form>

<script type="text/javascript">

// to remove from global namespace

(function() {

    function getRadioVal(form, name) {

        var val;

        var radios = form.elements[name];

        for (var i=0, len=radios.length; i<len; i++) {

            if ( radios[i].checked ) {

                val = radios[i].value;

                break;

            }

        }

        return val;

    }

    document.forms['demoForm'].elements['getVal'].onclick = function() {

        alert( 'The selected radio button\'s value is: ' + getRadioVal(this.form, 'ship') );

    };

    // disable submission of all forms on this page

    for (var i=0, len=document.forms.length; i<len; i++) {

        document.forms[i].onsubmit = function() { return false; };

    }

}());

</script>