element el-select選中事件（根據選中的值是否顯示時長的選擇框）

 效果圖：

1. html

 <span class="titleSize">處理</span>
          <el-form label-position="left">
            <el-form-item>
              <span class="dialogIitle"><span class="note">*</span>操作：</span>
              <el-select v-model="freezing_operation" placeholder="請選擇"  @change="freezing(freezing_operation)" clearable>
                <el-option
                    v-for="(key,value) in operation"
                    :key="value"
                    :label="key"
                    :value="value">
                  </el-option>
              </el-select>
            </el-form-item>
          </el-form>
           <el-form label-position="left">
          <el-form-item :style="styleObj">
            <span class="dialogIitle"><span class="note">*</span>時長：</span>
            <el-select v-model="duration" placeholder="請選擇" clearable>
              <el-option
                    v-for="(key,value) in days"
                    :key="key"
                    :label="value"
                    :value="key">
                    </el-option>
            </el-select>
          </el-form-item>
        </el-form>

2.js

 // 是否顯示時長
        freezing(val) {
           if(val==4 || val==6){
              this.styleObj.display ="none"
           }else{
             this.styleObj.display ="block"
           }
        },