TypeError：无法读取未定义的属性“ localeCompare”

Question

vue js的前端。我使用了引导表来显示数据。我想将数据作为行分组显示。所以我使用了引导表中的group-by-v2。那时候我遇到了错误.as TypeError：无法读取未定义的属性'localeCompare'

        <table id="runningbet-table"
               class="table"
                data-toolbar=".toolbar"
                data-search="true"
                data-show-refresh="true"
                data-show-toggle="true"
                data-show-columns="true"
                data-show-export="true"

                data-pagination="true"
                data-locale="en-US"
                data-page-list="[10, 25, 50, 100, ALL]"
                data-show-footer="false"
                data-toggle="context"
                data-target=".context-table"
                data-row-style="rowdollarStyles"
                data-group-by="true"
                  data-group-by-field="mode"
               >
            <thead>

            <tr >
                <th data-field="_id" data-class="d-none" >id</th>
               <th data-field="mode">Mode</th>
                <th data-field="results">Results</th>
                <th data-field="subs_mappings">Subcription</th>
                <th data-field="status">Status</th>
            </tr> 
            </thead>
            <tbody>
            </tbody>
            <tfoot>
            </tfoot>
        </table>

error：TypeError：无法读取未定义的属性'localeCompare'