Answers for "how to know selected radio"

Get the value of selected radio button

const selectedColor = document.querySelector('input[name="color"]:checked').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
      }