Answers for "how to get checked radio buttons"

get value of selected radio button using javascript

document.getElementById('submit').onclick = function() {
    var radios = document.getElementsByName('contact');
    for (var radio of radios)
    {
        if (radio.checked) {
            alert(radio.value);
        }
    }
}

check if one of the radio button is checked

if ($('input[name='+ radioName +']:checked').length) {
           // at least one of the radio buttons was checked
           return true; // allow whatever action would normally happen to continue
      }
      else {
           // no radio button was checked
           return false; // stop whatever action would normally happen
      }