Element獲取選中的下拉框的文本label

如下：

dom結構：

<el-select
    ref="nationalityIdSel"
    placeholder="請選擇"
    style="width:100%"
    clearable
    filterable
>
    <el-option
        v-for="(nationality,id) in nationalities"
        :value="id"
        :label="nationality"
        :key="id"
    ></el-option>
</el-select>

JavaScript：

this.$refs.nationalityIdSel.selectedLabel