JAVASCRIPT

jquery get value radio by name

var value = $('input[name="name_of_your_radiobutton"]:checked').val();

jquery select radio by name

$("input[type='radio'][name='theme']").click(function() {
    var value = $(this).val();
});

jquery select radio

$(function() {
    var $radios = $('input:radio[name=gender]');
    if($radios.is(':checked') === false) {
        $radios.filter('[value=Male]').prop('checked', true);
    }
});