通过jquery上下移动选择选项

<script src="https://cdn.jsdelivr.net/npm/jquery/dist/jquery.min.js"></script>

<ul id="option-list">
  <li>选项1</li>
  <li>选项2</li>
  <li>选项3</li>
  <li>选项4</li>
</ul>

$(document).ready(function() {
  var options = $('#option-list li');
  var selectedOption = null;

  $(document).keydown(function(e) {
    if (e.keyCode === 38) { // 上键
      if (selectedOption === null) {
        selectedOption = options.last();
      } else {
        selectedOption.removeClass('selected');
        selectedOption = selectedOption.prev();
        if (selectedOption.length === 0) {
          selectedOption = options.last();
        }
      }
    } else if (e.keyCode === 40) { // 下键
      if (selectedOption === null) {
        selectedOption = options.first();
      } else {
        selectedOption.removeClass('selected');
        selectedOption = selectedOption.next();
        if (selectedOption.length === 0) {
          selectedOption = options.first();
        }
      }
    }

    selectedOption.addClass('selected');
  });
});

.selected {
  background-color: yellow;
}