bootstrap下拉式多选框

详情参考：
https://www.cnblogs.com/landeanfen/p/7457283.html

---

index.html

<select id="usertype" name="usertype" class="selectpicker show-tick form-control" multiple data-live-search="false">
                        <option value="0">小学数学</option>
                        <option value="1">初一数学</option>
                        <option value="2">初二数学</option>
                        <option value="3">初一英语</option>
                        <option value="4">高一数学</option>
                        <option value="5">高二生物</option>
</select>

CSS引入：

<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.10.0/css/bootstrap-select.min.css">

JS引入：

  <!-- Latest compiled and minified JavaScript -->
  <script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.10.0/js/bootstrap-select.min.js"></script>

  <!-- (Optional) Latest compiled and minified JavaScript translation files -->
  <script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.10.0/js/i18n/defaults-*.min.js"></script>