JSONファイルの内容をHTML上に表示させたい

ソースコードは全て外部から引用したものです。

[リンク]　(https://developer.mozilla.org/ja/docs/Learn/JavaScript/Objects/JSON)

index.html

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src="js/jquery-3.4.1.min.js"></script>
  <script src="jsonData.js"></script>
</head>
<body>
  <header>
  </header>
  <section>
  </section>
</body>
</html>

jsonData.js

var header = document.querySelector('header');
    var section = document.querySelector('section');

    var requestURL = 'https://mdn.github.io/learning-area/javascript/oojs/json/superheroes.json';

    var request = new XMLHttpRequest();
    request.open('GET', requestURL);

    request.responseType = 'json';
    request.send();

    request.onload = function() {
      var superHeroes = request.response;
      populateHeader(superHeroes);
      showHeroes(superHeroes);
    }

    function populateHeader(jsonObj) {
      var myH1 = document.createElement('h1');
      myH1.textContent = jsonObj['squadName'];
      header.appendChild(myH1);

      var myPara = document.createElement('p');
      myPara.textContent = 'Hometown: ' + jsonObj['homeTown'] + ' // Formed: ' + jsonObj['formed'];
      header.appendChild(myPara);
    }

    function showHeroes(jsonObj) {
      var heroes = jsonObj['members'];
          
      for (var i = 0; i < heroes.length; i++) {
        var myArticle = document.createElement('article');
        var myH2 = document.createElement('h2');
        var myPara1 = document.createElement('p');
        var myPara2 = document.createElement('p');
        var myPara3 = document.createElement('p');
        var myList = document.createElement('ul');

        myH2.textContent = heroes[i].name;
        myPara1.textContent = 'Secret identity: ' + heroes[i].secretIdentity;
        myPara2.textContent = 'Age: ' + heroes[i].age;
        myPara3.textContent = 'Superpowers:';
            
        var superPowers = heroes[i].powers;
        for (var j = 0; j < superPowers.length; j++) {
          var listItem = document.createElement('li');
          listItem.textContent = superPowers[j];
          myList.appendChild(listItem);
        }

        myArticle.appendChild(myH2);
        myArticle.appendChild(myPara1);
        myArticle.appendChild(myPara2);
        myArticle.appendChild(myPara3);
        myArticle.appendChild(myList);

        section.appendChild(myArticle);
      }
    }