Приложение Todo: как динамически добавлять флажок и ввод текста при нажатии клавиши Enter в HTML с помощью JavaScript?

document.forms.form01.addEventListener('keydown', e => {
  switch(e.key) {
    case 'Enter':
      e.preventDefault();
      if (e.target.name == 'title'){
        add_item(e.target.form);
      }
      break;
    case 'Backspace':
      if (e.target.name == 'title' && e.target.value == ''){
        e.preventDefault();
        remove_item(e.target);
      }
      break;
  }
});

function add_item(form){
  // create the new todo item
  let fs = document.createElement('fieldset');
  let cb = document.createElement('input');
  cb.name = 'item';
  cb.type = 'checkbox';
  fs.append(cb);
  let tb = document.createElement('input');
  tb.name = 'title';
  tb.type = 'text';
  fs.append(tb);
  // add the todo item to the items fieldset
  form.items.append(fs);
  // set focus to the new text input
  tb.focus();
}

function remove_item(input) {
  let fs = input.closest('fieldset');
  // find the previous element
  let prev_fs = fs.previousElementSibling;
  // if there is a rev_fs set focus to the input
  // in the previous text input.
  // and delete the todo item/fieldset
  if (prev_fs){
    prev_fs.elements.title.focus();
    fs.remove();
  }
}

fieldset {
  border: none;
  margin: 0;
  padding: 0;
}

input[type = "text"] {
  border: none;
}

input[type = "text"]:focus {
  outline: none;
}

<form name = "form01">
  <fieldset name = "items">
    <fieldset>
      <input type = "checkbox" name = "item"><input type = "text" name = "title">
    </fieldset>
  </fieldset>
  <button type = "submit">Save</button>
</form>