javascript - 单击时减去选项本身的值

Question

我正在尝试在单击后更新选择框选项的值。它应该将所选值减去自身。

    <div class="pull-left col-xs-12 col-sm-4 col-md-4">

    <label for="rooms" style="color:black">No. of rooms: </label>
    <select required tabindex="10" id="selectBoxStandard" name="n_rooms">
      <option value="0">0</option>
      <option value="1">1</option>
      <option value="2">2</option>
      <option value="3">3</option>
      <option value="4">4</option>
      <option value="5">5</option>
      <option value="6">6</option>
      <option value="7">7</option>
     </select>
    </div>
<div class="button-style-1" style="padding-bottom:80px" style="padding-bottom:40px"><a href="javascript:standardRoom()" ><i class="fa fa-calendar"></i><span class="mobile-visibility">BOOK
                                      </span></a></div>

标准房间功能

    function standardRoom()
  {
     $('#selectBoxStandard option').val(Number($("#selectBoxStandard").val()) - Number($("#selectBoxStandard option").val()));
  }

如果点击后所选值为3，则剩余值应更新为:

    <div class="pull-left col-xs-12 col-sm-4 col-md-4">

    <label for="rooms" style="color:black">No. of rooms: </label>
    <select required tabindex="10" id="selectBoxStandard" name="n_rooms">
      <option value="0">0</option>
      <option value="1">1</option>
      <option value="2">2</option>
      <option value="3">3</option>
      <option value="4">4</option>
     </select>
    </div>

Answer 1

根据 option 值从 #selectBoxStandard 中删除最后一个子项:

$('button').on('click', standardRoom);

function standardRoom() {
  $('#selectBoxStandard').find("option:nth-last-child(-n+" + $('#selectBoxStandard').val() + ")").remove();
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<div class="pull-left col-xs-12 col-sm-4 col-md-4">

  <label for="rooms" style="color:black">No. of rooms: </label>
  <select required tabindex="10" id="selectBoxStandard" name="n_rooms">
    <option value="0">0</option>
    <option value="1">1</option>
    <option value="2">2</option>
    <option value="3">3</option>
    <option value="4">4</option>
    <option value="5">5</option>
    <option value="6">6</option>
    <option value="7">7</option>
  </select>
  <button>Update</button>
</div>