How to submit answers of a Javascript Quiz? [closed]

The quiz is written using vanilla Javascript and HTML:

<div class="quiz-container" id="quiz">
    <div class="quiz-header">
      <p>Please make sure to <a href="#">read the rules</a></p>
      <h1>Quiz</p>
      <h2 id="question">Question Text</h2>
      <ul>
        <li>
          <input type="radio" name="answer" id="a" class="answer">
          <label for="a" id="a_text">Answer</label>
        </li>
        <li>
          <input type="radio" name="answer" id="b" class="answer">
          <label for="b" id="b_text">Answer</label>
        </li>
        <li>
          <input type="radio" name="answer" id="c" class="answer">
          <label for="c" id="c_text">Answer</label>
        </li>
        <li>
          <input type="radio" name="answer" id="d" class="answer">
          <label for="d" id="d_text">Answer</label>
        </li>
      </ul>
    </div>
    <button id="submit">Next</button>
  </div>

At the end of the quiz, the results are shows to the user:

submitBtn.addEventListener('click', () => {
const answer = getSelected()
if(answer) {
   if(answer === quizData[currentQuiz].correct) {
       score++
   }
   currentQuiz++
   if(currentQuiz < quizData.length) {
       loadQuiz()
   } else {
    quiz.innerHTML = `
    <h2>You answered ${score}/${quizData.length} questions correctly</h2> 
    <input class="btn" type="button" onclick="window.open('mailto:email@email');" value="Submit results" />
    `
   }
}

What is the best way to possibly submit these answers to a backend? I know Javascript can’t blind submit results using mailto: as it’s client side, so any suggestions would be amazing.