<div class="container">
  <form id="form" class="py-3">
    <div>
      <label><input type="radio" name="color" value="red" checked> Red</label>
    </div>
    <div>
      <label><input type="radio" name="color" value="blue"> Blue</label>
    </div>
    <button class="btn btn-primary" type="submit">Submit</button>
  </form>
  <code id="result"></code>
</div>

const $form = document.getElementById('form')
const $result = document.getElementById('result')

$form.addEventListener('submit', function (e) {
  e.preventDefault()
  
  const value = $form.elements['color'].value
  
  $result.innerHTML = `color: ${value}`
})