Bootstrap select 多选并获取选中的值

代码：

<!DOCTYPE html>
<html>
 
<head>
    <meta charset="UTF-8">
    <script src="js/jquery-3.4.1.min.js" type="text/javascript" charset="utf-8"></script>
    <script src="https://cdn.staticfile.org/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
    <link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
    <!-- Latest compiled and minified CSS -->
    <link rel="stylesheet"
        href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.10.0/css/bootstrap-select.min.css">
 
    <!-- 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>
    <title></title>
</head>
 
<body id="">
    <div class="form-group">
        <!-- <div class="title">
                            可选择多个指标
                    </div> -->
        <div class="centent1Select">
            <select id="usertype" title="可选择多个指标" onchange="centent1SelectOnchang(this)"
                class="selectpicker show-tick form-control" multiple data-live-search="false">
                <option value="1">累计访问人数</option>
                <option value="2">打开次数</option>
                <option value="3">访问次数</option>
                <option value="4">访问人数</option>
                <option value="5">新访问人数</option>
                <option value="6">平均访问深度</option>
                <option value="7">次均停留时长</option>
                <option value="8">总添加人数</option>
                <option value="9">新添加人数</option>
                <option value="10">删除添加人数</option>
                <option value="11">分享次数</option>
                <option value="12">分享人数</option>
            </select>
        </div>
    </div>
    <script type="text/javascript">
        $(window).on('load', function () {
            $('#usertype').selectpicker({
                'selectedText': 'cat'
            });
        });
        //取出选择的任务执行人的方法
        function centent1SelectOnchang() {
            var val = "", staffs = [];
            //循环的取出插件选择的元素(通过是否添加了selected类名判断)
            for (var i = 0; i < $("li.selected").length; i++) {
                val = $("li.selected").eq(i).find(".text").text();
                if (val != '') {
                    staffs.push(val);
                }
            }
            console.log(staffs)
 
        }
    </script>
</body>
 
</html>