因为 before-upload 是指在文件上传之前、文件已被选中，但还没上传的时候触发，而设置了 :auto-upload=“false” 后，文件上传事件不被再次调用，，所以 before-upload 不生效，所以，限制图片大小和格式的时候，需绑定在 :on-change 里面

 	<el-upload
 		class="upload-demo uploadTwo"
 		ref="fileUploadRef"
 		:action="fileUrl + 'order/mdm/partpredictioncoord/import'"
 		:file-list="fileUploadList"
 		:auto-upload="false"
 		:headers="header"
 		name="uploadFile"
 		:limit="1" multiple
 		:on-change="beforeFeedBackExport"
 		:on-success="fileUploadSuccess">
        <span style="float: left; line-height: 32px; padding-right: 10px">反馈数据导入
        	<span style="color:red">*</span>：
        </span>
        <el-button
        	slot="trigger"
        	size="small"
        	type="primary"
        	style="float: right;"
        >
        	浏览
        </el-button>
     </el-upload>

 // 反馈数据导出
    beforeFeedBackExport(file) {

      // this.tableFileName = file.name;


      let testFile = file.name.substring(file.name.lastIndexOf('.') + 1).toLowerCase()

      const extension = testFile === 'xlsx' || testFile === 'xls';

      const isLt2M = (file.size / 1024 / 1024 < 10);
      if (!extension) {
        this.$message({
          message: '上传文件只能是xls/xlsx!',
          type: 'warning'
        });
        this.fileUploadList = []
        return false;
      }
      if (!isLt2M) {
        this.$message({
          message: "文件大小不可以超过10M",
          type: 'warning'
        });
        this.fileUploadList = []
        return false;
      }
      return (extension) && isLt2M
    },